Cub Cadet MTD P90 User Manual

Professional Shop Manual

P90 Series Vertical Shaft Engines

NOTE: These materials are for use by trained technicians who are experien ced in th e service an d re pair of outdoo r po wer equipment of the kind described in this publication, a nd are n ot intende d for use by un trained or ine xper ien ced individu als. These materials are intended to provide supplemental information to assist the trained technician. Untrained or inexperienced individuals should seek the assistance of an experienced and tr ained p rofessional. Read, understan d, and follo w all instructions and use common sense when working on power equipment. This includes the contents of the product’s Operators Manual, supplied with the equipment. No liability can be accepted for any inaccuracies or omission in this publication, although care has been taken to make it as co mpl ete and accu rate as possible at the time of publication. However, due to the variety of outdoor power equipment and continuing product changes that occur over time, updates will be made to these instructions from time to time. Therefore, it may be necessary to obtain the latest materials before servicing or repairing a product. The company reserves the right to make changes at any time to this publication without prior notice and without incurring an obligation to make such changes to previously published versions. Instructions, photographs and illustrations used in this publication are for reference use only and may not depict actual model and component parts.

Table of Contents

Chapter 1: Introduction

Professional Service Manual Intent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Assembly instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Model and serial number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Spark plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Air filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Oil type and capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Changing the oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Oil filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Oil pre-screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Fuel system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Servicing the fuel system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Fuel filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Valve lash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Exhaust system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Cleaning the engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

General torque specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Chapter 2: Basic Troubleshooting

Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Steps to troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Define the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Identify factors that could cause the problem . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Repairing the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Prime test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Leak-down test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Compression test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

PCV testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Chapter 3: Air Intake System

Air filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Blower/air filter housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Carburetor and Insulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Chapter 4: The Fuel System and Governor

Inspecting the fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Test fuel for alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Choke/throttle cable adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Carburetors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Inspecting the carburetor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Disassembly and rebuilding the carburetor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Engine speed adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Afterfire solenoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Testing the afterfire solenoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Governor arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Governor shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Governor cup and the governor gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Chapter 5: Lubrication

Oil type and quantity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Oil dipstick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Dip stick tube removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Lubrication system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Testing the oil Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Positive crankcase ventilation valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Chapter 6: Starter and Charging Systems

Starter removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Bench testing the electric starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Rebuilding the starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Charging system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Charging system testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Stator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Chapter 7: Ignition System

Troubleshooting the ignition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

The module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Module removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Installing the module and setting the air gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Flywheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Cleaning the spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Inspection of the spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Spark plug removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Chapter 8: Exhaust

Spark arrestor (if equipped) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Muffler removal/replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Catalytic converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Chapter 9: Cylinder Head

Cylinder head removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Cylinder head installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Push rod guide plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Chapter 10: Crankshaft, piston and Connecting Rod

Crankshaft inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Piston Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Connecting rod inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Cylinder inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Balance Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Engine specifications chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Engine torque values chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Chapter 11: Failure Analysis

Abrasive Ingestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Insufficient lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Engine Overspeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Overheated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Mechanical Breakage/ Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Detonation/preignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

III

Introduction

CHAPTER 1: INTRODUCTION

Professional Service Manual Intent

This manual is intended to provide service dealers with an introduction to proven diagnostic and repair proce-

dures for MTD P90 series vertical shaft engines. Disclaimer: The information contained in this manual is correct at the time of writin g. Both the prod u ct an d th e inf or -

mation about the product are subject to change without notice. About the text format:

NOTE: Is used to point out information that is relevant to the procedure, but does not fit as a step in the proce -

dure.

• Bullet points: indicate sub-steps or points.

! CA UTION! CA UTION

! WA RNING! WA RNING

! DANGER! DANGER

1. Numbered steps indicate specific things that should be done, and the order in which they should be done . 1a. Substeps will be lettered and nested within steps. Two or more substeps may be combined to describe

the actions required to complete a step.

Disclaimer: This manual is intended for use by trained, professional technicians.

• Common sense in operation and safety is assumed.

• In no event shall MTD be liable for poor text interpretation or poor execution of the procedures described

in the text.

Caution is used to point out potential danger to the technician, operator, bystanders, or surrounding property.

Warning indicates a potentially hazardous situation that, if not avoided, could result in death or serious injury.

Danger indicates an imminently hazardous situation that, if not avoided, will result in death or serious injury. This signal word is to be limited to the most extreme situations

• If the person using this manual is uncomfortable with any procedures they encounter, they should seek

the help of a qualified technician or MTD Technical Support.

Safety

This Service Manual is meant to be used along with the Operator’s Manual. Read the Operator’s Manual and familiarize yourself with the safety and operational instructions for the equipment being worked on. Keep a copy of the Operator’s Manual for quick reference. Operator’s manuals may be viewed for free at the brand support website. It will be necessary to have the complete model and serial number for the equipment.

P90 Series Vertical Shaft Engines

• Be prepared in case of emergency:

! CAUTION! CAUTION

Keep a fire extinguisher nearby Keep a first aid kit nearby Keep emergency contact numbers handy

• Replace any missing or damaged safety labels on shop equipment.

• Replace any missing or damaged safety labels on equipment being serviced.

• Grooming and attire:

! WARNING! WARNING

! CAUTION! CAUTION

Do not wear loose fitting clothing that may become entangled in equipment. Long hair should be secured to prevent entanglement in equipment.

Jewelry is best removed.

• Protective gear: includes, but is not limited to

Clear eye protection ................................ while working around any machinery

Protective gloves ..................................... where necessary

Armored footwear.................................... when working around any machinery

Hearing protection ................................... in noisy environments

Chemically resistant gloves..................... when working with chemicals or solvents

Respirator................................................ when working with chemical or solvents

Appropriate tinted eye protection............. when cutting or welding

Flame resistant headgear, jacket, chaps. when cutting or welding

• Remember that some hazards have a cumulative effect. A single exposure may cause little or no harm, but continual or repeated exposure may cause very serious harm.

• Clean spills and fix obviously dangerous conditions as soon as they are noticed.

! DANGER! DANGER

• Lift and support heavy objects safely and securely.

• Be aware of your surroundings and potential hazards that are inherent to all power equipment. All the labels in the world cannot protect a technician from an instant of carelessness.

• Exhaust fumes from running engines contain carbon monoxide (CO). Carbon monoxide is a colorless odorless gas that is fatal if inhaled in sufficient quantity. Only run engines in well ventilated areas. If running engines indoors, use an exhaust evacuation system with adequate make-up air ventilated into the shop.

Introduction

Fasteners

• Most of the fasteners used on the MTD engine are metric. Some are fractional inches. For this reason, wrench sizes are frequently identified in the text, and measurements are given in U.S. and metric scales.

• If a fastener has a locking feature that has worn, replace the fastener or apply a small amount of releasable thread locking compound such as Loctite® 242 (blue).

• Some fasteners, like cotter pins, are single-use items that are not to be reused. Other fasteners such as lock washers, retaining rings, and internal cotter pins (hairpin clips) may be reused if they do not show signs of wear or damage. This manual leaves that decision to the judgement of the technician.

Assembly instructions

• Torque specifications may be noted in the part of the text that covers assembly. They may be summarized in tables along with special instructions regarding locking or lubrication. Whichever method is more appropriate will be used. In many cases, both will be used so that the manual is handy as a quick-reference guide as well as a step-by-step procedure guide that does not require the user to hunt for information.

• Lubricant quantity and specification may be noted in the part of the text that covers maintenance, and again in the section that covers assembly. They may also be summarized in tables along with special instructions. Whichever method is more appropriate will be used. In many cases, the information will be found in several places in the manual so that the manual is handy as a quick-r eference g uide as we ll as a step-by-step procedure guide that does not require the user to hunt for information.

• The level of assembly instructions provided will be determined by the complexity of reassembly, and by the potential for damage or unsafe conditions to arise from mistakes made in assembly.

• Some instructions may refer to other parts of the manual for subsidiary procedures. This avoids repeating the same procedure two or three times in the manual.

P90 Series Vertical Shaft Engines

MTD Vertical Engine Model Designators

• Starter/Alternator

1=Recoi l star t

• 2=Elect ric star t (12V)

• 3=E. start/alt. 18W

• 4=E. start/alt. 3A/5A

• 5= AutoChoke / Recoil

• 6= AutoChoke /Elec tric Start

• 7= AutoChoke /Elec tric Start/Alt

P= Vertica l (1 cyl.) Q= Vertical (2 cyl.)

1 P 6 1 M U A

Major Revision Change

Compliance

U United States (50 State) HEurope C California 0 (Zero) 49 State G U.S .(49 ) and Europe W U.S.( 50) an d Europe

Bore Dia. (mm)

End Product

B Mower ( long shaft M0) C Chi pper/Sh redd er M Mower ( long shaft/no shrou d) D Mower (long shaft M 1) N Mower (short shaft M0) E Mower ( short shaft M1) P Mower ( long shaft M0) F Mower (short shaft/no shrou d) Q Mower (short shaft M0) R Mower (long shaft/ no shroud) T Till er

L Log split ter W Worl d Til ler

Model number

MTD Engine Serial Numbers

1P65FH/0510271A0023

MonthYear

Producing Line# and Shift#: 1A=L ine 1, 1 1B=L ine 1, 2 2A=L ine 2, 1 2B=L ine 2, 2 3A=L ine 3, 1 3B=L ine 3, 2 4A=L ine 4, 1 4B=Line 4, 2nd Shift

Date

st nd st nd st nd st

Shift

Engine number

Introduction

Model and serial number

The model and serial number can be found on a white sticker with a bar code. The sticker is located between the dipstick and the muffler. See Figure 1.1.

Model /serial number

Oil screen

Muffler

Dipstick

Figure 1.1

NOTE: The serial number will always start with the model number.

Maintenance

The recommended maintenance intervals listed in this manual are a guideline. They are ad justable for local con-

ditions.

Maintenance items Interval

Oil Change* 50 hrs Oil filter 200 hours Oil pre-screen Annually Clean the air filter 100 hrs Replace the air filter 200 hrs Spark plugs 100 hrs Fuel filter 100 hrs Clean the engine 100 hours

* First oil change at 5 hours.

P90 Series Vertical Shaft Engines

Spark plugs

The information in this manual applies to the MTD engine. Some basic principles may apply to engines produced by other manufacturers.

As the saying goes “an ounce of prevention is worth a pound of cure”. The same can be said about preventive maintenance on outdoor power equipment. By changing the spark plug and oil at recommended intervals many fai lures can be avoided.

NOTE: Please refer to Chapter 7: Ignition for the

complete service instructions on spark plugs.

1. The spark plug used in the MTD engine is a F6RTC (part # 951-10292) gapped to 0.024” - 0 .031” (0.60 -

0.80 mm).

2. Wear rate will vary somewhat with severity of use. If the edges of the center electrode are rounded-off, or any other apparent wear / damage occurs, replace the spark plug before operating failure (no start) occurs.

3. Cleaning the spark plug:

See Figure 1.2.

Figure 1.2

NOTE: MTD does not recommend cleaning spark plugs. Use of a wire brush may leave metal deposits on the

insulator that causes the spark plug to short out and fail to spark. Use of abrasive blast for cleaning may cause damage to ceramic insulator or leave blast media in the recesses of the spark plug. When the media comes loose during engine operation, severe and non-warrantable engine damage may result.

4. Inspection of the spark plug can provide indications of th e op er a ting con d ition of th e en gine .

• Light tan colored deposits on insulator and electrodes is normal.

• Dry, black deposits on the insulator and electrod es indicate an over-rich fuel / air mixture (too much fuel or

not enough air)

• Wet, black deposits on the insulator and electrodes indicate the presence of oil in the combustion cham-

ber.

• Heat damaged (melted electrodes / cracked insulator / metal transfer deposits) may indicate detonation.

• A spark plug that is wet with fuel indicates that fuel is present in the combustion chamber, but it is not

being ignited.

Air filter

Paper-pleated element

Introduction

Generally air filters come in two different types, a pleated-paper element or foam. A combination of the two are

used on the MTD engine. See Figure 1.3.

1. The main function of the air filter is to trap air borne particles before they enter the engine. Dirt ingestion can cause serious internal engine damage.

2. Air filters used on the MTD engine are designed to prevent particles larger than 3-5 micron from p assing through into the engine.

Foam pre-filter

Figure 1.3

NOTE: Never use compressed air on a paper air filter . Compressed air will remove the tiny fibers that are used

to catch the dirt in the air. Without these fibers the filter is useless.

6. Foam pre-filters can be washed in warm soapy water. NOTE: When drying a foam filter either squeeze it inside of a paper towel or let it air dry. DO NOT wring it

because the filter will tear.

7. Before installing any foam filter, after it has been washed, it needs to be free of moisture.

NOTE: Always check with factory specification prior to servicing/replacing any engine components. NOTE: Do not oil the foam pre-filter. The paper filer will absorb the oil and it will become plugged.

3. The filter should b e checked on a regular basis p ossibly several times in a season.

4. Typically an air filter should be ch anged befo re every season.

5. If a foam air pr e-clean er is di rty, but not in bad of condition, it can be cleaned and reused. The paper pleated filters can be shaken or lightly tapped to free the debris from the filter.

P90 Series Vertical Shaft Engines

Oil type and capacity

The recommended oil for MTD engines is an SAE 10W-30 oil with an SM API rating or better . The oil cap acity for

all of the P90 series engines is 57 fl.oz (1.7 liters).

• Check the oil level daily and change the oil more frequently in severe operating conditions such as high ambient temperature, dusty conditions, or high load use in exceptionally thick grass.

• Synthetic oil is a suitable alternative, but it does not extend service intervals.

NOTE: MTD recommends the use of petroleum oil during the break in period to ensure the piston rings cor-

rectly break in.

• Synthetic vs. Petroleum based oil: To simply look at synthetic oil and to compare it with Petroleum based oil there is very little difference. However, when you look at the two thro ugh a micro scope it is easy to see the difference. Synthetic is made up of smaller molecules. This allows the oil to get into areas that petroleum based oil cannot.

• No oil additives or viscosity modifiers are recommended. The performance of a good oil meeting the API specifications will not be improved by oil additives.

NOTE: Some oil additives may cause severe and non warrantable engine damage, constituting a lubrication

failure.

NOTE: If the oil is noticeably thin, or smells of gasoline, a carburetor repair may be needed before the engine

can be run safely.

To check the oil:

1. Twist and remove the dipstick from the engine.

2. Clean the oil off of the tip of the dipstick.

3. Re-insert the dipstick and turn it until it is fully seated to get the oil level reading.

4. The oil level is determined by the highest point on the dipstick that is completely covered with oil.

See Figure 1.4.

Fully seat the dip stick before reading it

Figure 1.4

Changing the oil

Introduction

The oil change interval is every 100 hrs. NOTE: The first oil change should be preformed at 8

hours.

NOTE: The oil filter should be replaced when the oil is

changed.

To change the oil:

1. Remove the cap from the oil drain. See Figure 1.5.

Figure 1.5

Figure 1.6

Oil drain

1/2” hose

2. Remove the dipstick.

3. Slide a piece of 1/2” hose onto the drain. See Figure 1.6.

4. Route the other end of the hose into an approved oil drain pan.

5. Turn the oil drain a quarter turn counter-clockwise to unlock it, then pull out 3/8” (9.5 mm) to open the valve.

6. After all of the oil has been drained, close the oil drain by pushing it in and turning it back a quarter turn.

7. Remove the drain hose.

8. Place the cap back on the oil drain.

9. Fill engine with 57 oz (1.7 L) of SAE 10W-30 oil with a SM API rating or better.

NOTE: Refer to the oil chart to determine the proper

weight of oil to use.

10. Check the dip stick to verify that the oil is at the proper level before returning to service.

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P90 Series Vertical Shaft Engines

Oil filter

To replace the oil filter:

1. Drain the oil by following the steps described in the previous section of this chapter.

2. Clean the area around the oil filter

3. Remove the oil filter by turning it counter-clockwise, as seen from the left side of the engine. See Figure 1.7.

4. Place a light coating of oil on the O-ring of the new filter.

5. Pre-fill the new filter with fresh, clean oil.

6. Thread the new filter on to the engine. Hand tighten only .

7. Fill engine with 57 oz (1.7 L) of SAE 10W-30 oil with a SM API rating or better.

8. Test run the engine and check for leaks before returning the engine to service.

Oil pre-screen

To clean the pre-screen:

1. Drain the oil by following the procedures described in the previous section of this chapter.

2. Remove the pre-screen plug using a 15/16” wrench. NOTE: There is a spring that will come out with the

plug.

See Figure 1.8.

3. Remove the screen.

4. Inspect the o-ring for signs of damage or wear. Replace the o-ring if any are found.

5. Clean the screen in parts cleaning solution.

6. Rinse the screen in warm water.

Oil filter

Figure 1.7

Pre-screen

Spring

Plug

7. Dry the screen using compressed air.

8. Install the screen.

9. Install the plug and spring.

10. Fill engine with 57 oz (1.7 L) of SAE 10W-30 oil with a SM API rating or better.

11. Test run the engine and check for leaks before returning the engine to service.

Figure 1.8

Introduction

Fuel system

What you should know about fuel.

Most of the fuel presently available in North America is oxygenated to some extent. This is commonly done through the addition of ethanol. Most engines offered for sale on outdoor power equipment in the North American markets are designed to tolerate no more than 10% ethanol by volume

Ethanol is hygroscopic, meaning it absorbs water. If left exposed to air, it will draw water out of the air.

Ethanol is an oxygenator, which means that it will oxidize (corrode) metal that it comes into contact with. Exposure to air causes fuel to go bad quickly, leaving gum and varnish deposits.

Fuel used in Cub Cadet outdoor power equipment should be no more than 30 days old. Because it may already have been stored at the refinery or gas station for a week or more, fuel should be purchased in small quantities and stored in safety approved gas cans with the caps closed.

For storage, all fuel should be run out of the tank and engine. Anti-oxidation additives will help keep the fuel fresher.

Servicing the fuel system

Inspect the fuel system every time the engine is operated. If dirty fuel is found in the fuel tank or fuel that does not smell “right”, drain the fuel tank and replace the fuel filter. Dispose of bad fuel in a safe and legal manner.

Refer to the units service manual for the procedures to drain the fuel tank.

! CAUTION! CAUTION

Fuel filter

2. Squeeze the tabs on the fuel line clamps and slide them away from the filter.

3. Carefully slide the fuel lines off of the filter. If there are pieces of rubber on the barbs of the fuel filter, replace

the affected fuel line. IMPORTANT: The P90 series engines uses low permeation fuel line to meet EPA guidelines. When replacing

4. Install the new filter by following the above steps in reverse order.

5. Test run the engine and check for leaks before returning to service.

Gasoline and its vapors are extremely flammable. Use common sense when working around the fuel system. Avoid sparks, open flames or heat sources that can ignite the fuel vapors.

A dirty fuel filter can result in a lean run condition. The fuel filter should be replaced every 100 hours.

To replace the fuel filter: NOTE: The part number for the fuel filter is BS - 29 8090S.

It is a 150 micron (red) filter. Use of a filter with a lower micron rating will cause fuel starvation issues.

1. Clamp off the fuel lines to prevent fuel from leaking

Fuel filter

Figure 1.9

the fuel lines, they must be replaced with the same type of low permeation fuel line.

when the lines are disconnected.

NOTE: Take care that the fuel lines are not damaged

when clamping them off. Never insert a screw or anything else into the fuel line to prevent fuel from coming out. This will damage the inside of the fuel line.

NOTE: There are commercially available fuel line clamp-

ing tools that will not damage the fuel lines.

See Figure 1.9.

P90 Series Vertical Shaft Engines

Valve lash

Valve lash is the clearance between the top of the valve stem and the rocker arm. The valve lash should be checked after the first 25 hours of use and ever y 100 hour s a f ter th at. Valve lash can be checke d and adju sted using the following steps:.

1. If the engine has been run, allow it to cool thor-

oughly. Position the mower for easy access to the cylinder head.

2. Disconnect the high-tension lead from the spark

plug and ground it well away from the spark plug hole.

3. Remove the spark plug using a 13/16” or 21mm

wrench. A flexible coupling or “wobbly” extension may help.

4. Remove the four bolts that secure the valve cover

using a 10mm wrench, and remove the valve cover from the engine.

NOTE: If care is used not to damage the valve

5. Confirm that the piston is at Top-Dead-Center on

the compression stroke.

See Figure 1.10.

cover gasket, it can be re-used.

See Figure 1.11.

High tension lead

Muffler

Figure 1.10

Probe to confirm piston

is at top of travel

Valve cover

• The compression stroke ca n be distin g uis he d from the overlap stroke by the presence of air pressure at the spark plug hole and the fact that neither of the valves should move significantly on the compression stroke.

• There is an automatic compression release mechanism that “bumps” the exhaust valve as the piston rises on the compression stroke. At TDC, the exhaust valve should be fully closed.

Valves closed

(push rods slack)

Figure 1.11

.005” feeler

gauge

Figure 1.12

Introduction

6. Check valve lash between each valve stem and rocker arm using a feeler gauge.

7. Intake valve lash (top valve) should be 0.004” -

0.006” (0.10 - 0.15mm).

8. Exhaust valve lash (bottom valve) shou ld be 0 .006” -

0.008” (0.15 - 0.20mm).

See Figure 1.12.

See Figure 1.13.

9. Use a 10mm wrench to loosen the jam nut, and a 14mm wrench to adjust the rocker arm fulcrum nut. See Figure 1.13.

• Tighten the rocker arm fulcrum nut to close-up the

clearance between the end of the valve stem and the contact point on the rocker arm.

.007” feeler

gauge

Figure 1.13

11. Double-check the clearance after tightening the jam nut, to confirm that it did not shift. Re-adjust if necessary.

12. Rotate the engine through several compression cycles:

• Obse rv e th e mo ve m en t of th e valv e ge ar.

• Return the piston to TDC compression stroke and re-check the valve lash to confirm consistent movement of the valve gear, including the slight bump to the exhaust valve from the automatic compression release.

13. Clean-up any oil around the valve cover opening, clean the valve cover, replace the valve cover gasket if necessary.

14. Install the valve cover, tightening the valve cover screws to a torque of 62 - 80 in-lbs (7 - 9 Nm).

• Loosen the rocker arm fulcrum nut to open-up the clearance between the end of the valve stem and the contact point on the rocker arm.

10. Hold the fulcrum nut with a 14mm wrench, tighten the jam nut to a torque of 80 - 106 in-lb. (9 - 12 Nm) using a 10mm wrench.

IMPORTANT: Over tightening the valve cover will cause it to leak.

15. Install the spark plug.

16. Test run the engine before returning it to service.

P90 Series Vertical Shaft Engines

Exhaust system

The exhaust system is a frequently overlooked component of an engine. It is important to make sure the muf f ler is in good condition and free of blockage.

NOTE: A blocked muffler will result in poor performance. If a muffler is completely blocked, the engine may not start.

Cleaning the engine

1. To maintain a proper operating temperature and to keep the equipment looking good, all debris should be removed from the engine.

2. It is recommended to use compressed air to blow all of the debris off of the engine. NOTE: A pressure washer may be used to clean outdoor power equipment but only after the unit has been

allowed to properly cool.

General torque specifications

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Useful Engine Specifications

Description SAE Metric

Engine displacement 25.6 cubic inch 420 cc

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P1 P1 P1

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Spark plug gap 0.024” - 0.031” 0.6 - 0.8 mm Spark plug torque 177 - 221 in lbs 20 - 25 Nm Ignition module air gap 0.016” - 0.024” 0.4 - 0.6 mm Intake valve lash 0.004” - 0.006” 0.10 - 0.15 mm Exhaust valve lash 0.006” - 0.008” 0.15 - 0.20 mm Oil capacity 57 oz 1.7 L

BASIC TROUBLESHOOTING

CHAPTER 2: BASIC TROUBLESHOOTING

Definitions

Troubleshooting - The act of gathering information by preforming tests and direct observations. Diagnosis

shooting.

Introduction

Diagnosing an engine is an art form that is built upon several factors. First and most importantly is a good understanding of how the engine works. The second is skills that have been honed by experience. Finally the use of visual observations and a structured, systematic approach to troubleshooting a problem.

The first part of this chapter will outline the steps of troubleshooting an engine so a technician can form a proper diagnosis. The second half of this chapter will describe specific procedures and tests to perform while troubleshooting.

Steps to troubleshooting

Define the problem

The first step in troubleshooting is to define the problem:

- Developing and testing theories of what the problem is, based on the information gathered in trouble-

The first two rules in troubleshooting is to cause no further harm to the engine and prevent

! CA UTION! CA UTION

NOTE: The steps and the order of the steps that follow are a suggested approach to tro ubleshoo ting the MTD

• Crankshaft will not turn.

injuries. Always make sure to check the oil for level and condition before starting an engin e. Also check attachments for damage and make sure they are firmly mounted.

engine. The technician does not necessarily have to follow them as described in this chapter.

A. Starter not working B. Engine in a bind (external - attachment jammed) C. Engine in a bind (internal - engine seized)

• Crankshaft turns, no start

• Starts, runs poorly A. St arts, then dies B. Runs with low power output C. Make s unusual smoke when running

I. Black smoke, usually heavy II. White smoke, usually heavy III. Blue smoke. usually light

D. Makes unusual sounds when running

I. Knock II. Click III. Chirp

P90 Series Vertical Shaft Engines

IV. Unusual exhaust tone

There are tools that the technician can use in order to define the problem, such as:

1. Interview the customer. 1a. Get a good description of their complaint. 1b. If it is an intermittent problem, verify what conditions aggravate the problem as best as possible. 1c. Get an accurate service history of the equipment. 1d. Find out how the customer uses and stores the equipment.

2. Direct observation: 2a. Do not automatically accept that the customer is correct with their description of the problem. Try to

duplicate the problem.

2b. Check the general condition of the equipment (visually).

I. Cleanliness of the equipment will indicate the level of care the equipment has received. II. Make sure the engine and attachments are securely fastened. III. The tune-up factors.

NOTE: Most hard starting and poor running conditions can be solved by performing a tune-up.

a. Check the condition and amount of oil in the crankcase. b. Check the level and condition of the fuel. c. Check the ignition and “read” the spark plug. d. Look for obvious signs of physical damage, exhaust system blockage or cooling system block-

age.

Identify factors that could cause the problem

This is the second step in the troubleshooting process.

1. Crankshaft will not turn. A. Starter not working. This can be an electrical failure or a mechanical failure. The likely suspects are:

I. A dead battery. II. A bad ground III. A failure in the electrical circuit. IV. A failure of the starter itself.

B. Engine in a bind (external - atta ch men t jamme d) . T his usual ly indicates that the unit be ing power ed by

the engine either failed or has something jammed in it, locking up the system.

C. Engine in a bind (internal - engine seized). This is usually either a quick fix or a catastrophic failure. The

likely suspects are: I. Complete hydraulic lock (easy fix). II. Bent crankshaft (unrepairable) III. Internal binding, crankshaft, connecting rod or piston (unrepairable)

BASIC TROUBLESHOOTING

2. Crankshaft turns, no start.

2a. Most gasoline engine diagnosis involves isolating problems in the four critical factors an engine needs to

run properly:

I. Ignition- sufficient spark to st art combustion in the cylinder, occurring at the right time. II. Compression- enough pressure in the cylinder to convert combustion into kinetic motion. It also

needs sufficient sealing to generate the vacuum needed to draw in and atomize the next intake charge.

III. Fuel- correct type and grade of fresh gasoline; in sufficient quantity, atomized (tiny droplet s) an d in

correct fuel/air proportions.

IV. Flow- if all of the above conditions are met but the flow of air is constricted on the inlet or exhaust

side, it will cause the engine to run poorly or not at all. This also includes ensuring the valves are timed to open at the proper time.

2a. Isolate the ignition system and compression from the fuel system by preforming a prime test.

I. Burns prime and dies. This would indicate a fuel system issue. II. Does not burn prime. Not a fuel system issue. Check for an ignition, compression or flow problem.

2c. Compression or ignition problem

I. Check the engine stop and safety switch. II. Test the ignition system using a proper tester. III. Replace the spark plug with a new one or a known good one. IV. Check compression or leak down. V. Check valve lash. VI. Check valve timing/actuation. VII. Check exhaust.

3. Starts, runs poorly

3a. Starts, then dies

P90 Series Vertical Shaft Engines

I. Run the engine with a sp ark tester in-line between the spark plug wir e and the spark plug or use a n

oscilloscope and see if the spark goes away at the same time the engine dies.

II. Check choke operation.

a. Black smoke? b. Wet plug?

III. Prime test immediately after engine dies. If it restarts, this may indicate a problem with fuel flow to

the carburetor. Check the gas cap, fuel line, fuel filter, and the float in the carburetor.

3b. Runs with low power output.

I. Look for unusual exhaust color (smoke). II. Unusually hot muffler (may glow red).

a. Retarded ignition b. Exhaust valve opening early (lash too tight)

III. Mechanical bind

a. A slightly bent crankshaft. In some cases the drag may increase and decrease as the crankshaf t

rotates. This produces a pulsing feeling that is different than a jerk back. b. Parasitic external load. A bind in the equipment the engine is powering. c. Internal drag from a scored piston or similar damage.

IV. Low governor setting or stuck governor.

a. Check RPMs using a tachometer. b. RPMs should not droop under moderate to heavy loads.

V. Low compression

a. Check valve lash b. Check compression c. Check leak down to identify the source of the compression loss.

VI. Flow blockage

a. Exhaust blockage, usually accompanied by an unusual exhaust sound.

• Just as a throttle on the carburetor controls the engine RPMs by limiting the amount of air an engine can breathe in, an exhaust blockage will limit engine performance by constricting the other end of the system.

• The muffler itself my be blocked.

• The exhaust valve may not be opening fully, possibly because of extremely loose valve lash settings.

• The exhaust valve seat may have come loose in the cylinder head. This may cause a loss of compression, a flow blockage or it may randomly alternate between the two.

NOTE: The cause of an exhaust valve coming loose is usually over heating.

b. Intake blockage

• An intake blockage up-stream of the carburetor will cause a rich fuel/air mixture and constrict the amount of air that the engine can draw in, limiting performanc e.

• T he intake valv e no t fully open i ng . A poss ible cause of this is loose valve lash.

BASIC TROUBLESHOOTING

V. Makes unusual smoke when running

a. Black smoke, usually heavy, usually indicates a rich air fuel mixture

• Not enough air: air flow blockage or a partially closed choke.

• Too much fuel: carburetor float or float valve stuck or metering / emulsion issues with the carburetor.

b. White smoke, usually heavy

• Oil in muffler, usually the result of improper tipping. The engine will “fog” for a minute or so, then clear-up on its own.

• Massive oil dilution with gasoline. It may be caused by improper tipping. It can also be caused by leaky carburetor float valve, if there is a down-hill path from the carburetor to the intake port. Check oil for gasoline smell, repair carburetor.

c. Blue smoke, usually light.

PCV system

• May be blocked or unplugged.

• May be over-come by massive over-filling or oil dilution with gasoline.

• Will cause oil to exit the engine via any low-resistance paths.

Piston rings

• Confirm with leak-down test.

• Smoke will be more pronounced under load.

• Repair may not make economic sense.

Valve guides (and intake valve stem seal).

• Smoke will be more pronounced on over-run.

VI. Makes unusual noise when running

a. Knock

• Check for loose mounting of engine or driven implement

• Rotate crankshaft back-and-forth to check for loose connecting rod.

b. Click

• Clicks and pops on engine shut-down: Compression release coming into play as the engine RPMs cross the activation threshold. This will have no ill effects on engine performance.

• Half-engine speed clatter: loose valve lash.

• Half-engine speed clatter, slightly heavier: wrist-pin.

• Rhythmic heavy-light engine speed click: piston slap

c. Spark-knock

• Advanced ignition timing

• Low octane fuel

• Over-heating engine (check for blocked cooling air flow)

• Carbon build-up in cylinder: glowing carbon chunks pre-igniting air fuel mix.

d. Chirp

• Compression, blowing-by the fire-ring of a damaged head gasket will sometimes produce a

P90 Series Vertical Shaft Engines

chirping noise.

• Confirm with a compression test and leak-down test.

e. Unusual exhaust tone

Splashy or blatty

• Splashy idle usually indicates a slight rich condition.

• May indicate an exhaust blockage, usually slightly muffled. Backfire

• On over-run: unburned fuel igniting past exhaust valve. Mixture not burning completely in combustion chamber. It may be too rich or it may be spark-plug or ignition problem.

• Occasional, under load: engine momentarily runs lean, usually will cycle with float bowl level or governor pull-in, sometimes sounds like a slight stumble. Ethanol content exceeding 10% will make the engine run artificially lean.

Skip

• Usually ignition related.

• Run the engine with a spark tester in-line between the spark plug wire and the spark plug or use an oscilloscope and see if the spark goes away at the same time the engine dies.

4. Engine over-speed A. Continual over-speed

• Binding or damaged external governor linkage or carburetor throttle.

• Mis-adjusted governor arm.

• Internal governor failure.

B. Momentary over-speed

• Intermittent bind (very unusual).

• Interference: This is fairly common when debris can fall on the governor linkage during normal operations.

5. Engine RPMs surge (hunting) A. Over-governed condition- Return spring replaced with wrong part or hooked into wrong hole.

NOTE: This is an extremely rare condition, usually created by tampering.

B. Lean Air-fuel mixture condition- When AFR (Air Fuel Ratio) is significantly below stoichiometric ratio

(14.7:1) engine RPMs sink until they reach a po int tha t can be su pp or te d by the availa b l e fuel . Th is causes a momentary surge in power until the available fuel is consumed, then the RPMs fall again, repeating the cycle.

• Too much air: look for an air leak in the intake tract

• Not enough fuel: look for fuel supply or carburetor problems

BASIC TROUBLESHOOTING

Repairing the problem

The third step in the troubleshooting process is to repair the problem. This step consists of:

A. Form a diagnosis by using all of the information gathere d from the tro ub leshooting th at was p erforme d. B. Physically perform the repair.

The fourth, and hopefully final, step in the troubleshooting process is the follow through. This step consists of:

A. Thoroughly test the repaired equipment: confirming that the initial diagnosis was correct. If it was

wrong, start the troubleshooting process over again.

NOTE: Sometimes the engine will have multiple problems at the same time. By performing one repair, other

issues may show up that are unrelated to the first repair.

B. Delivery to customer: We are not just repairing equipment, we are repairing customers.

• Inoculate against recurring problem with education, e.g.: if the problem was caused by stale fuel, make sure the customer is aware that fuel go es bad ove r tim e.

• M ak e s ure th e cu sto m er und er stands th e re pair, preventing “superstitious” come-backs.

P90 Series Vertical Shaft Engines

Prime test

To perform a prime test:

1. Prime the engine through the carburetor throat using a squirt bottle, filled with clean fresh gasoline.

2. Make sure the throttle is in the run position.

3. Attempt to start the engine.

4. If the engine starts and runs long enough to burn the prime, the problem is effectively isolated to the fuel system. Proceed to Chapter 4: The Fuel System and Governor.

5. If the engine did not start, check ignition system as described in Chapter 7: Ignition System.

6. If the ignition system is working, check the compression or perform a leak down test.

Leak-down test

A leak-down test is the preferred method to test the engine’s ability to compress the charge. It will also show where pressure is leaking from.

To perform a leak-down test:

NOTE: A leak down test pressurizes the combustion chamber with an external air source and will allow the

technician to listen for air “leaking“ at the valves, piston rings and the head gasket.

NOTE: These are general instructions. Read and follow the instructions that came with the tester before

attempting to perform this test.

• If possible, run the engine for 3-5 minutes to warm up the engine.

• Remove the spark plug and air filter.

• Find top dead center of the compression stroke.

! CA UTION! CAUTION

1. Find top dead center by following the steps described in the valve lash section of Chapter 1: Introduction

2. Thread the leak down tester adapter into the spark plug hole.

3. Connect tester to compressed air.

If the engine is not centered at top dead center, the engine will rotate when compressed air is introduce to the combustion chamber.

Leak down

tester

See Figure 2.1.

4. Adjust the regulator knob until the needle on the gauge is in the yellow or set area of the gauge.

5. Connect the tester to the adapter. NOTE: If the engine rotates it was not at top dead

center.

6. Check the reading on the gauge.

Leak-down

tester adapter

Figure 2.1

7. Compare the results to the following chart.

Leak-down Testing Results

Symptom Possible cause

BASIC TROUBLESHOOTING

Air escaping from the breather

Air escaping from the exhaust

Air escaping from the carburetor

Gauge reading low

Gauge reading moderate

Gauge reading high

Worn cylinder or piston rings. Possible blown head gasket

Leaking exhaust valve

Leaking intake valve

Cylinder and piston rings are in good condition

There is some wear in the engine, but it is still usable

excessive wear of cylinder and/ or piston rings. Engine should be short blocked or it could be a blown head gasket.

P90 Series Vertical Shaft Engines

Compression test

To perform a compression test:

NOTE: Compression should be in the range of 55 - 80 PSI (3.8 - 5.5 Bar).

• Disconnect the high-tension lead from the spark plug and ground it well away from the spark plug hole.

• Remove the spark plug using a 13/16” or 21mm wrench. A flexible coupling or “wobbly” extension may

help.

• Pull the starter rope several times to purge any fuel or oil from the combustion chamber. NOTE: Air compresses readily, liquid does not. Liquid in the combustion chamber will result in an artificially

high compression reading.

1. Install a compression gauge in the spar k pl ug hole.

2. Confirm that the gauge is “zeroed”, then pull the starter rope repeatedly, until the needle on the gauge stops rising.

3. Interpreting compression readings.

See Figure 2.2.

Compression Readings

Readings in

psi

<20 (1.4 Bar)

Most likely a stuck valve or too tight of a valve lash, provided the starter rope pulls with normal effort.

Compression gauge

Figure 2.2

Possible causes

20 - 55 (1.4-3.8 Bar)

55 - 80 (3.8-5.5 Bar)

>80 (>5.5 Bar)

Valve seat damage or piston ring and/or cylinder wear.

Normal readings

Excessive valve lash, a partial hydraulic lock, a bad cam or a bad automatic compression relief.

BASIC TROUBLESHOOTING

PCV testing

The PCV (Positive Crankcase V e nt ilation) valve is located in the engine block and allows the cr an kcase pr essu re to escape.

Leakage and blockage are the two failure modes for a PCV system. Either mode will cause crankcase pressure to build-up, though the effects of a blocked PCV are generally more dramatic. Increased case pressure will result in oil entering the combustion chamber.

1. The PCV chamber is vented to the intake manifold

crankcase

air chamber

through a rubber hose. The rubber hose directs crankcase fumes to the heat box assembly. See Figure 2.3.

2. When functioning prop erly, the PCV valve works with the inherent pumping action of the piston in the bore to expel pressure from the crankcase.

NOTE: Normally, small engines run with slightly negative

case pressure. This case pressure can be mea sured using a slack-tube water manometer, or an electronic version of the same tool. Less than -3” to -4” (-7.6 - 10.2cm) of water is a typical reading at idle.

Figure 2.3

• Oil will be forced by the rings and valve guides, being burnt in the combustion chamber.

• The cause of this oil burning can be mistaken for a worn-out engine, if proper diagno sis (compression, leakdown, and case pressure) is not performed.

4. Experimentation by MTD’s Training and Education Department has revealed the following characteristics of MTD engines:

• A leaky PCV system will not build-up substantial case pressure.

• A leaky PCV system will allow the engine to ingest contaminants through the system, accelerating engine wear.

• A blocked PCV system will allow crankcase pressure to build very rapidly . Noticeable oil fumes will be evident in the exhaust within several minutes of normal operation.

3. An engine th at fails to p urge extra case pressure in a controlled manner will build case pressure. The pres sure will find it’s own way out of the engine in undesirable ways.

P90 Series Vertical Shaft Engines

Air filter

AIR INTAKE SYSTEM

CHAPTER 3: AIR INTAKE SYSTEM

Paper-pleated element

Foam pre-filter

Figure 3.1

Air filter cover

Generally air filters come in two different types, a pleated-paper element or foam. A combination of the two are

used on the MTD engine. See Figure 3.1.

• Air filters used on the MTD engine are designed to

prevent particles larger than 3-5 micron from pass ing through into the engine.

• The filter should be checked on a regular basis

possibly several times in a season.

NOTE: Never use compressed air on a paper air filter.

Compressed air will remove the tiny fibers that are used to catch the dirt in the air. Without these fibers the filter is useless.

NOTE: Refer to Chapter 1: Introduction for the mainte-

nance interval and cleaning instructions for the air filter.

To remove/replace the air filter:

1. Wipe down the air filter housing to preven t an y de bris from getting into the engine.

Figure 3.2

2. Un-screw the two wing nuts. See Figure 3.2.

NOTE: The wing nuts are part of the air filter cove r and do

not come off.

P90 Series Vertical Shaft Engines

3. Lift the air filter cover off the engine.

4. Remove the air filter assembly.

5. Install the air filter by following the previous steps in reverse order.

Air filter

Figure 3.3

NOTE: The air filter housing is part of the blower

cover. The intake manifold extends through a hole in the bottom of the air filter housing. When installing the air filter, the hole in the bottom of the paper element must fit over the intake manifold.

NOTE: A light coating of oil can be applied to the

hole in the air filter. This will allow the filter to slide over the manifold without distorting.

See Figure 3.4.

Manifold

Figure 3.4

Blower/air filter housing

Figure 3.5

AIR INTAKE SYSTEM

On the P90 series of engine, the air filter housing is part of the blower housing.

To remove/replace the blower/air filter housing:

1. Remove the air filter following the steps described in the previous section of this chapter.

2. Remove the n ut that was under the air filter (ind icated by the arrow in

Figure 3.5.) using a 10mm wrench.

Control panel

Choke lever

Figure 3.6

3. Loosen the two shoulder bolts (indicated by the arrows in

4. Remove the three acorn nuts (indicated by the arrows in

5. Lift the blower/air filter housing off of the engine.

6. Install the blower/air filter housing by following the previous steps in reverse order.

Figure 3.6.) using a 12 mm wrench.

Figure 3.7.) using a 10 mm wrench.

Figure 3.7

NOTE: tighten the blower/air filter housing nut s to a torque

of 80 - 106 in lbs (9 - 12 Nm).

7. Test run the engine before returning it to service.

P90 Series Vertical Shaft Engines

Carburetor and Insulator

To remove/replace the carburetor and insulator block:

1. Remove the blower/air filter housing by following the steps described in the blower/air filter housing sec tion of this chapter.

2. Disconnect the breather hose from the intake manifold. See Figure 3.8.

NOTE: On units equipped with an evaporative emis-

sions system, disconnect the hose from the EVAP port of the intake manifold.

NOTE: If a unit does not have EVAP emissions sys-

tem, the EVAP port on the intake manifold will have a plug on it.

3. Remove the intake manifold by removing the two nuts (indicated by the arrows in 10 mm wrench.

To avoid personal injury or prop-

! WAR N IN G! WAR N IN G

extremely flammable and the vapors are explosive. Serious personal injury can occur when gasoline is spilled on yourself and/or your clothes which can ignite. Wash your skin and change clothes immediately

erty damage, use extreme care in handling gasoline. Gasoline is

Figure 3.8.) using a

EVAP port

Breather hose

Figure 3.8

4. Clamp off the fuel line to prevent fuel from leaking when the line is disconnected.

IMPORTANT: Take care that the fuel lines are not

damaged when clamping them off. Never insert a screw or anything else into the fuel line to prevent fuel from coming out. This will damage the inside of the fuel line.

NOTE: There are commercially availa b le ho se

pinching pliers that will not damage the fuel lines.

5. Disconnect the fuel line from the carburetor. NOTE: MTD uses low permeation fuel lines to meet EPA guidelines. Low permeation fuel lines are made with

a soft membrane that lines the inside of the line. Any tear in this membrane will allow the fuel to get in between the membrane and the hose, choking off the fuel flow.

NOTE: Every time the fuel line is pulled off of a brass nipple, the fuel line must be replaced with the same type

of low permeation fuel line.

See Figure 3.9.

Hose pinching pliers

Figure 3.9

Double nut

Figure 3.10

AIR INTAKE SYSTEM

6. Double nut the carburetor studs and remove them. See Figure 3.10.

NOTE: The insulator block and gaskets may fall out when

the studs are removed.

NOTE: The most likely reason to remove the insulator

block and its gaskets is to cure a lean running con dition. Inspect all removed parts carefully to identify the point where additional air is entering the intake tract.

7. Disconnect the choke linkage.

8. Disconnect the thr ottle linkage and spring.

9. Turn the carburetor upside down.

Figure 3.11

10. Remove the afterfire solenoid by removing the two screws (indicated by the arrows in

NOTE: The screws are installed with a th read locking com-

pound. It may be necessary to use a #2 phillips driver with a ratchet in order to get enough torque to loosen the screws.

NOTE: There is an O-ring between the afterfire solenoid

and the carburetor . It is import ant that the O-ring is in place when re-installing the afterfire solenoid.

NOTE: The carburetors are not inter -changeable from one

engine model to another. To help prevent carbure tor mix-ups, the engine model number is stamped on the carburetor by the fuel nipple. See Figure 3.12.

NOTE: Some red paint was smeared onto the carburetor

so that the numbers will stand out in the photo graph.

Figure 3.11.).

Engine model number

Figure 3.12

P90 Series Vertical Shaft Engines

1 1. Install the carburetor by following the p revious steps

in reverse order. NOTE: Use new gaskets between the cylinder

head, the insulator, the carburetor and the intake manifold.

Gasket

NOTE: Tighten the ca rburetor nut s to a torque of 62

- 80 in lbs (7 - 9 Nm).

12. Test run the engine before returning it to service.

Studs

Insulator

Figure 3.13

Carburetor

Manifold

FUEL SYSTEM AND GOVERNOR

CHAPTER 4: THE FUEL SYSTEM AND GOVERNOR

The function of the fuel system is to store fuel, mix the fuel with air in the correct ratio and deliver it to the intake

port. The fuel system consists of the following components:

• Fuel tank

• Fuel lines

• Fuel filter

• Carburetor and insulator block NOTE: When working on the fuel systems, look at the whole system. A problem will rarely be isolated to one

component.

Inspecting the fuel

NOTE: Fuel is the maintenance item most often overlooked by consume rs. A lot of f uel systems prob lems are

caused by gas that is out of date or fuel with too much alcohol in it. When inspecting the fuel:

• Look for water.

• Look for dirt.

• Look for discoloration.

• Sniff carefully to see if it smells like varnish or kerosene.

• Save th e fu el to sh ow to cust om e r.

• Look for oil in the fuel.

• Test the fuel for alcohol content if there is a reason to suspect it.

NOTE: Save a sample of the fuel collected to show the customer. NOTE: Customers pouring engine oil into the fuel tank seems to be a growing problem.

P90 Series Vertical Shaft Engines

Test fuel for alcohol

Fuels currently on the market contain a wide array of additives. Some of these additives oxygenate the fuel. Oxygenated fuel reduces emissions, and is required in some parts of the United States. Fuel make-up varies seasonally and geographically. Ethanol is the primary additive used to oxygenate fuel.

Ethanol in fuel creates a lot of problems for gasoline engines. The biggest problem is that alcohol attracts and holds water. Th is corrod es the met a l components of the fuel system, especially the carburetor. Alcohol also does not produce as much heat as gasoline when burnt and it burns at a different stoichiometric ratio. This results in less power for the engine.

A 10% ethanol (E10) mix is acceptable for MTD engines. Anything higher than that will result in performance issues.

NOTE: E15 and E85 fuels are not to be used in any

MTD engines.

There are several alcohol test kit available commercially. See Figure 4.1.

Generally these kits involve mixing a measured amount of water and gas together and seeing were the boundary layer is.

The test kit should come with a chart to compare the boundary layer height to alcohol percentage.

See Figure 4.2.

Figure 4.1

Figure 4.2

Choke/throttle cable adjustment

FUEL SYSTEM AND GOVERNOR

The choke/throttle cable will need to be adjusted any time the cable or the control panel is replaced.

Choke lever

High speed stop screw

Figure 4.3

NOTE: The procedures to remove/replace the choke/throt-

tle cable can be found in the service manual for the piece of equipment that the engine is mounted to.

NOTE: The choke should be opened when the engine

starts. This can be a source of starting issues with customers who are not familiar with manual chokes.

The choke is controlled by the throttle linkage. When properly adjusted, the high speed throttle stop screw should be touching the choke lever but not pushing it. See Figure 4.3.

NOTE: The guard was removed in the picture for clarity.

To adjust the choke/throttle cable:

1. Insert a #1 phillips screw driver into the alignment hole in the control panel and guard.

2. Loosen the cable clamp.

3. Verify that the high speed stop screw is just touching the choke lever

• If the screw does not touch the lever, tighten the

screw until it just touches the lever.

See Figure 4.4.

#1 phillips screw driver

Figure 4.4

Throttle control lever

• If the screw is pushing on the lever, back the screw

out until it no longer touches the lever. Then tighten the screw until it just touches the lever.

4. Move the throttle control lever to the detent between full throttle and the choke position.

5. Tighten the cable clamp to lock the throttle cable in place.

6. Verify that the throttle cable will move the choke to the closed position.

7. Start the engine and check the maximum engine speed. Adjust it as needed by following the proce dures described in the engine speed adjustment section of this chapter.

See Figure 4.5.

Figure 4.5

P90 Series Vertical Shaft Engines

Carburetors

If diagnosis indicates a fuel problem, inspect the carburetor. This is important even if problems are identified

elsewhere in the fuel system.

IMPORTANT: The fuel must be tested for alcohol content before diagnosing anything else on the engine. NOTE: It is important to perform a compression or leak down te st befor e conde mnin g a car bur etor. An engine

can have a borderline compression reading and not create enough of a vacuum to draw in a sufficient fuel/air charge.

NOTE: To determine if border-line compression is the problem; remove the spark plug. Squirt a little bit of oil

into the combustion chamber to seal the rings. Reinst all the spark plug. If the engine st arts and runs ok, then that was the problem. If it does not start, move on to the carburetor.

Inspecting the carburetor

1. Remove the float bowl and check for dirt and/or varnish.

2. Inspect the needle valve and needle valve seat for dirt and/or damage.

3. Inspect the gaskets and O-rings for damage.

4. Inspect the vents and orifices, verify that they are free of debris. NOTE: If a little cleaning and new gaskets will fix the carburetor, do it. If the carburetor requires extensive

cleaning; it is better to replace the carburetor.

IMPORTANT: Never try to mechanically clean orifices. That will damage them and ruin the carburetor. NOTE: The jet markings (if present) may be used for identification purposes, but the technician should not

attempt to infer orifice sizes from the identification numbers.

NOTE: Installing the wrong main jet, or a carburetor with the wrong main jet will produce performance and

emissions issues.

FUEL SYSTEM AND GOVERNOR

Disassembly and rebuilding the carburetor

1. Remove the carburetor by following the procedures described in Chapter 3: Air Int ake System. NOTE: An insulator separates the carburetor from the cylinder head.

• A bowl vent port is in a recessed passage on the end of the carburetor that faces the insulator.

• A second passage in the insulator supplements the passage on the carburetor.

• Gaskets separate the insulator from the cylinder head and the carburetor from the insulator.

• A port in the carburetor to insulator gasket ties the bowl vent passages together.

2. Check the vent passages. See Figure 4.6.

3. Check the gaskets and the insulator block.

4. Remove the afterfire solenoid seat using a 14mm wrench.

NOTE: From this point an assessment can be made about

See Figure 4.7.

the viability of rebuilding the carburetor.

Bowl vent port

Afterfire solenoid

seat

Figure 4.6

Figure 4.7

Bowl vent

channel

Float pin

• If extensive corrosion is evident, replace the carbu-

retor.

• If varnish build-up is too extensive to clean,

replace the carburetor.

5. Remove the pin that the float hinges on to remove the float.

P90 Series Vertical Shaft Engines

NOTE: Because the float valve is crucial to the func-

tioning of the carburetor and the viton tip of the valve is subject to wear, technicians should replace the valve and spring any time the carburetor is disassembled for cleaning.

NOTE: If the needle seat is worn or damaged, the

carburetor must be replaced.

6. Remove the main jet using a narrow-shank straight blade screwdriver.

See Figure 4.9.

Float

Float valve

Compression

spring

Figure 4.8

• A square cross-section gasket seals the bowl to

the body of the carburetor.

NOTE: Fuel enters the central column through a

port about 1/2” (1cm) from the bottom to help prevent the ingress of any residue in the bot tom of the bowl.

NOTE: The orifice in the main jet meters fuel into

the central column.

NOTE: Air from the main jet emulsion port enters

the central column near the top, then gets bubbled through the emulsion tube into the metered fuel flow to promote atomization.

NOTE: The main jet secures the emulsion tube in the

central column of the carburetor. See Figure 4.10.

Main jet

Bowl gasket

Main jet

Figure 4.9

Emulsion tube

Figure 4.10

Welch plug

Shot plug in

feed bore Fuel port to

central column

Throttle stop

screw

Figure 4.11

Fuel feed leg on central column for pilot and transition

FUEL SYSTEM AND GOVERNOR

7. The throttle stop screw has a large pliable lip around the head of the screw. That lip secures a metering plug for the pilot and transition ports. Remove the screw to reach the plug.

8. Carefully pry out the metering plug and spacer using a small screwdriver.

See Figure 4.11.

See Figure 4.12.

Spacer

Metering

plug

Figure 4.12

O-rings

NOTE: Do not remove the throttle shaft. The screws that

hold the throttle plate to the throttle shaft are peened. When they are removed, they will expand the holes in the throttle shaft, ruining it.

NOTE: Do not try to remove the choke shaft. The plastic

end of the shaft is molded over a grove to hold it in place. Prying on it will break the shaft.

End view

9. Examine the metering plug: See Figure 4.13.

• Fuel, drawn from the central column via the long

fuel feed leg, is metered by the brass orific e in th e tip of the metering plug.

• Air, drawn fr om the emulsion air port, is metered by

the size of the brass orifice at the entrance to the port.

Air passage

Fuel metering orifice

Figure 4.13

• The fuel and air that feed the pilot and transition

ports are mixed at the metering plug.

• The metering plug creates a small venturi. The

pressure drop of the air passing throu gh the me ter ing plug draws the fuel into the passage to the pilot and transition ports, in an emulsified mixture.

P90 Series Vertical Shaft Engines

NOTE: The pilot screw regulates how much of this

pre-mixed fuel/air emulsion is allowed to enter the throat of the carburetor, to atomize down-stream of the throttle plate. On current production units, it is set at the factory and the screw head is removed. See Figure 4.14.

NOTE: The transition ports are fixed. They are

drilled into the throat of the carburetor, down-stream of the venturi. They lie behind the brass welch plug near the pilot screw.

10. Soak the Carburetor body in a suitable solvent until clean.

NOTE: Ultrasonic cleaning using a suitable water/

detergent mixture will clean carburetors safely and effectively.

11. Rinse it thoroughly.

12. Dry the carburetor body using compressed air.

Transition ports Pilot port

Pilot screw (before head is removed)

Figure 4.14

13. Reassemble the carburetor and install it by following steps 1-8 in reverse order.

14. Start the engine and check the idle RPM using a tachometer.

15. Check the top no load speed of the engine. NOTE: The top no-load speed of the engin e is 3300 RP M’s + 100.

16. Adjust the engine speed as needed by following the procedures described in the speed adjustment section of this chapter.

17. Test run the engine before returning it to service.

Engine speed adjustment

FUEL SYSTEM AND GOVERNOR

To adjust the engine speed:

Tab

1. Start the engine and let it reach operating temperature.

2. Move the throttle control lever to the full throttle position.

3. Measure the engine’s speed using a tachometer.

4. Bend the tab, that the governor spring is attached to, as needed to adjust the engine speed to 3,300 RPM + 100. See Figure 4.15.

• Bend the tab up to increase speed.

• Bend the tab down to decrease speed.

Figure 4.15

P90 Series Vertical Shaft Engines

Afterfire solenoid

When an engine is turned off, the engine does not “instantly” stop spinning. As the engine slows down, it is still drawing fuel out of the carburetor. This raw fuel passes through the engine because the ignition system is grounded to prevent the spark plug from firing. When the raw fuel reaches the hot muf fler it can ignite, resulting in an afterfire.

An Afterfire solenoid is an electromechanical device that prevents fuel fro m reaching the main jet in the carburetor when the ignition key is turned to the “off” position. Generally this will prevent an afterfire. Fuel will still be drawn into the engine from the idle port, but the fuel/air mixture will be too lean to burn.

NOTE: If the throttle is moved to the idle position when turning off the engine, the fuel/air mixture ratio will be

in a range that will support combustion resulting in an afterfire.

To remove/replace an afterfire solenoid:

1. Remove the carburetor by following the procedures

described in Chapter 3: Air Intake System.

2. Disconnect the ground lead using a 10 mm wrench.

See Figure 4.16.

3. Disconnect the power lead.

NOTE: The oil dipstick can be removed for more

access to the power lead; however, it can be difficult to re-install the dipstick tube without shearing the O-rings.

Ground lead

Figure 4.16

Power lead

Old style

New style

Figure 4.17

FUEL SYSTEM AND GOVERNOR

NOTE: Early production engines have a simple bullet con-

nector between the stator and the af terfire solenoid (power lead). Current production engines have locking bullet connectors. The two connectors are not interchangeable. All new stators and afterfire solenoids sold as service parts will have the new connectors.

NOTE: All service replacement stators and afterfire sole-

noids will be shipped with an adaptor and an instruction sheet on how to use the adaptor, if needed.

4. Mark or note the routing of the afterfire solenoid’s power lead.

Power lead

Figure 4.18

5. Remove the after fire solenoid.

6. Install the a fter fire solenoid by following the previous steps in reverse order.

NOTE: Make sure the power lead is routed properly to pr e-

vent damage to the wire.

7. Test run the engine before returning it to service.

P90 Series Vertical Shaft Engines

Testing the afterfire solenoid

An afterfire solenoid that is not working properly can prevent the engine from starting. The solenoid itself rarely

fails, usually there is some type of fault in the wiring to the solenoid to prevent it from energizing.

To determine if the afterfire solenoid is faulty:

1. Test the unit’s battery.

• The battery must be fully charged before any testing can be preformed.

2. Turn the ignition key on and off while holding the afterfire solenoid.

• An audible click should be heard and a “thump”

should be felt when the key is turned on.

• If the thump is felt or the click is heard, the wir-

ing is most likely working properly. Bench test the solenoid.

• If nothing is felt or heard, investigate the wiring

before condemning the solenoid.

Afterfire solenoid

Figure 4.19

3. Check the ground lead of the afterfire solenoid . NOTE: Running a jumper wire from the negative

post of the unit’s battery directly to the sole noids ground lead is the fastest way to test the ground.

NOTE: Do not try to ground the solenoid housing.

The coil inside the solenoid is insulated from the housing.

4. Repeat step 1.

• If the solenoid is now working, repair the

ground connection.

See Figure 4.20.

Jumper wire

Figure 4.20

Afterfire solenoid lead from main harness

Figure 4.21

FUEL SYSTEM AND GOVERNOR

5. With the ignition key in the “on” position, test for voltage at the power lead connection. See Figure 4.21.

• If battery voltage is present, bench test the sole-

noid.

• If the voltage at the connection is not the same as

the battery voltage or there is no voltage, the pro b lem is with the equipment’s electrical system and not the solenoid. Follow the troubleshoot proce dures found in the appropriate service manual for that piece of equipment.

Bench testing the solenoid

To bench test the solenoid:

Ground lead

1. Remove the afterfire solenoid by following the procedures described in the afterfire solenoid section of this chapter.

2. Connect the ground lead of the solenoid to the negative side of a 12 volt power supply

NOTE: A battery charger set to the trickle charge (2 amp)

setting works fine for this test.

3. Connect the power lead of the solenoid to the positive side of the power source while watching the solenoid’s plunger.

• If the plunger does not retract, the solenoid is

faulty and must be replaced.

• If the plunger does retract, there is most likely an

increased resistance type of failure in the equip ment’s electrical system. Perform voltage drop tests to find the source of the resistance.

Extended

Retracted

Figure 4.22

P90 Series Vertical Shaft Engines

Governor

The engine speed is controlled by a balance between the force applied by a spring (pulling the thro ttle open) and a flyweight mechanism within the engine apply ing force to the governor arm (pushing the throttle closed). See Figure 4.23.

NOTE: While the mechanism is simple and robust,

it is important to pay attention when working on parts near the governor. Binding caused by interference with mis-routed lines or cables may make the governor unrespon sive.

NOTE: When a governed engine “hunts”, it is gen-

erally an indication of a lean fuel/air mixture, rather than a problem with the governor.

Governor arm

To remove the governor arm from the governor shaft:

Throttle linkage

Spring tension

Governor action

Governor spring

Figure 4.23

1. Remove the two screws, indicated by the arrows in Figure 4.24., that hold the governor guard in place using a 8 mm wrench.

2. Lift the guard up and hold it out of the way. NOTE: The fuel line is attached to the guard with

two barbed eyelets. It is not necessary to disconnect the fuel line from the guard, but doing so will make it easier to access the governor arm.

3. Remove the throttle cable clamp.

4. Disconnect the throttle cable.

5. Remove the upper screw that holds the control panel to the engine block.

6. Loosen the lower screw that holds the control panel to the engine block.

7. Swing the control panel towards the front of the engine.

See Figure 4.25.

Figure 4.24

upper screw

Figure 4.25

T-bolt

Figure 4.26

To install the governor arm:

1. Attach the throttle linkage and return spring.

FUEL SYSTEM AND GOVERNOR

8. Put an alignment mark on the governor arm and shaft.

See Figure 4.26.

9. Loosen the nut and T-bolt that secures the governor arm to the shaft.

10. Carefully spread open the seam on the arm.

11. Carefully slide the Governor arm off of the governor shaft.

12. Unhook the governor linage and throttle return spring.

13. Unhook the governor spring.

2. Attach the governor spring

3. Rotate the governor shaft clockwise until it stops.

4. Slide the arm onto the shaft. The flat on the top of the shaft should be roughly parallel to the arm that connects to the spring.

NOTE: There is a hairpin clip that keeps the gove rnor shaft from sliding into the engine. It may be necessary to hold the shaft while sliding the arm on to prevent the hairpin clip from “popping off” and allowing the governor shaft to fall into the engine.

NOTE: The alignment marks from the previous section can help align the arm.

5. Tighten the nut on the clamp bolt to secure the arm.

6. Install the screw removed from the throttle control plate.

7. Tighten the lower screw of the throttle control plate.

8. Install the governor guard.

9. Adjust the governor to maintain top no-l oad speed as descr ibed in the throttle and choke adjustment se ction of this chapter.

See Figure 4.26.

P90 Series Vertical Shaft Engines

Governor shaft

To remove or replace the governor shaft:

1. Remove the engine from the equipment that it powers.

2. Remove the governor arm by following the procedures described in the governor arm section of this chapter.

3. Remove the sump cover by following the steps described in Chapter 10: Cam, Crankshaft and Pis ton.

4. Remove the hairpin clip from the governor shaft. See Figure 4.27.

5. Slide the governor arm out of the engine block from the inside of the engine.

6. Check the movement of the fly-weights and cap on the governor gear.

7. Install the shaft by following the above steps in reverse order.

hairpin clip

8. Install the engine on the equipment it powers.

9. Test run th e en gin e and adju st th e to p no load engine rpms by following the steps described in the throttle and choke adjustment section of this chap ter.

Governor cup and the governor gear

The Governor gear and cup are located inside the

crankcase cover. See Figure 4.28.

The flyweights and the governor cup are interlocked on this family of engines. The governor gear and cup are not serviceable. If there is a failure of the governor gear, cup or flyweights, the sump cover must be replaced as an assembly.

Figure 4.27

Governor gear

Oil pump

Figure 4.28

Lubrication

CHAPTER 5: LUBRICATION

Oil type and quantity

The recommended oil for MTD engines is an SAE 10W-30 oil with an SM API rating or better . The oil capacity for

all of the P90 series engines is 57 fl.oz (1.7 liters).

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• If the oil is noticeably thin, or smells of gasoline, carburetor repair may be needed before the engine can be run safely.

• Check the oil level frequently and change the oil more frequently in severe operating conditions such as exceptionally deep snow falls.

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• Synthetic oil is a suitable alternative, but it does not extend service intervals.

NOTE: MTD recommends the use of petroleum oil during the break in period to ensure the piston rings correctly break in.

Synthetic vs. Petroleum based oil: To simply look at synthetic oil and to compare it with Petroleum based oil there is very little difference. However , when you look at the two through a micr oscope it is easy to see the dif ference. Synthetic is made up of smaller molecules. This allows the oil to get into areas that petroleum based oil cannot.

P90 Series Vertical Shaft Engines

Oil dipstick

To check the oil:

1. Twist and remove the dipstick from the engine.

2. Clean the oil off of the tip of the dipstick.

3. Re-insert the dipstick and turn it until it is fully seated to get the oil level reading.

4. The oil level is determined by the highest point on the dipstick that is completely covered with oil.

Dip stick tube removal

To remove/replace the dip stick tube:

1. Remove the blower/air filter housing by following the procedures described in Chapter 3: Air Intake Sys tem.

2. Remove the screw that passes through the fle xible clamp and the dipstick tube mounting flange using a 10 mm wrench.

3. Rotate the tube until the mounting flange clears the flywheel.

See Figure 5.2.

See Figure 5.1.

Fully seat the dip stick

before reading it

Dipstick

Figure 5.1

Dipstick tube

Flexible clamp

4. Pull the dip stick tube out of the engine block.

5. Inspect the O-rings on the dip stick and the dip stick tube. Replace if damaged.

6. Install by following the above steps in reverse order.

NOTE: Lubricate the O-rings for installation. NOTE: Keep extra O-rings on hand. It is very easy to shear the O-rings when installing the dipstick tube. NOTE: Compressing the O-rings while inserting the dipstick tube will help prevent shearing the O-rings.

Figure 5.2

Lubrication system

Oil filter

Dipper

Figure 5.3

Balance shaft

Oil pump

Lubrication

The 4P90 engine uses a combination pressurized and splash lubrication system. T sump that is driven by the balance shaft.

The oil is drawn into the pump through a pre-screen. The pump pushes the oil through a relief valve then into the oil filter. From the filter, the oil flows through a passage in the sump cover until it reaches the crankshaft PTO bearing. The oil passes through the P TO bearing and is forced into a passage in the crankshaft. The oil follows this passage to the crankshaft crankpin. It is forced out between the crankshaft and the connecting rod.

The rest of the engine is lubricated by the oil mist created by the moving parts in the sump.

The oil in the head drains back into the sump through a passage cast into the cylinder block.

Testing the oil Pump

here is an oil pump in the

Kohler oil pressure tester

Figure 5.4

Adapter

To test the oil pump:

1. Allow the engine to cool.

2. Connect an oil pressure tester to the engine. NOTE: There are two methods that can be used to con-

nect an oil pressure tester:

A. Kohler oil pressure test kit #25 761 06-S

1a. Remove the oil filter. 1b. Thread the oil pressure tester onto the oil filter

nipple.

See Figure 5.4.

B. Connecting an oil gauge to the port in the sump

cover.

1a. Remove the oil plug from behind the oil filter

base using a 12mm wrench.

1b. Install an M8 x 1.25 male to 1/8” NPT female

adapter on to the oil pressure gauge.

Figure 5.5

NOTE: Mem-co part # ”M8 to 1/8 F” can be used.

1c. Thread hose and adapter from oil pressure

gauge into the port hand tight.

P90 Series Vertical Shaft Engines

2. Check the oil level. NOTE: Top off the oil as needed with an SAE 10W-

30 oil with an SM API rating or better

3. Start the engine.

4. Let the engine run until the oil reaches operating tempurature 176

5. With the engine at 3,300 RPM, the oil pressure should reading be a minimum of 5 psi (0.3 bar). See Figure 5.6.

NOTE: A reading below what is specified could be

the result of:

° - 212° (80° - 100°C).

• Clogged oil screen

• Failed oil pump

• The oil pump gear failed

• The pressure relief valve is stuck open.

• Worn PTO bearing

• Worn rod bearing

• Engine is filled with the wrong oil. NOTE: The pressure relief valve is not accessible. If it fails, the sump cover must be replaced.

• The ring gear on the balance shaft or the crankshaft (very rare).

Figure 5.6

Positive crankcase ventilation valve

Lubrication

The PCV valve is located under the flywheel and allows the crankcase pressure to escape. The function and test procedures for the PCV is covered in Chapter 2: Basic Troubleshooting.

To service the PCV:

Figure 5.7

PCV cover

Fiber disc

Spring

Gasket

1. Remove the flywheel by following the steps describe d in the Chapter 7: Ignition System.

2. Remove the five screws that hold the PCV chamber cover to the engine block using a 10mm wrench . See Figure 5.7.

3. The cover and gasket can be separated from the chamber.

NOTE: The dimple in the cover helps locate the fiber disc

over the port that leads into the crankcase.

See Figure 5.8.

Figure 5.8

Spring

Wire mesh

Figure 5.9

4. Inspect the disc for any signs of dirt, damage or leaking.

5. Inspect the folded wire mesh in the chamber. See Figure 5.9.

Fiber disc

P90 Series Vertical Shaft Engines

6. Inspect the oil drain-back port. Make sure it will allow oil to drain back into the engine. See Figure 5.10.

7. Reassemble the PCV valve.

8. Tighten the cover bolts to a torque of 53 - 71 in lbs (6 - 8Nm).

9. Inspect the PCV tubing for cracks, brittleness or signs of leaking. Replace the PCV tube if any are found.

See Figure 5.11.

Oil drain port

Figure 5.10

PCV chamber cover

10. Re-assemble the engine by following the above steps in reverse order.

11. Test run the engine before returning to service.

PCV tubing

Figure 5.11

Starter removal

CHAPTER 6: STARTER AND CHARGING SYSTEMS

To remo ve /r ep lace the starter assembly:

Starter screws

Starter cable

1. Disconnect the negative battery cable.

2. Disconnect the starter cable using a 10 mm wrench.

3. Remove the two screws that secure the st arter to th e engine using a 12 mm wrench.

Starter and Charging System

See Figure 6.1.

Figure 6.1

Figure 6.2

4. Slide the st arter off of the do wel pins, indicated by the arrows in

5. Install the starter by following the previous steps in reverse order.

NOTE: Tighten the starter screws to a torque of 16 - 18 ft

lbs (22 - 25 Nm).

6. Test run the engine before returning it to service.

Figure 6.2.

P90 Series Vertical Shaft Engines

Bench testing the electric starter

IMPORTANT: Always bench test an electric starter

before condemning it.

To bench test an electric starter:

1. Remove the starter by following the procedures described in the previous section of this chapter.

2. Mount the starter in a vise. NOTE: If the vise is tightened too tight, the starter

can be crushed.

3. Attach the negative lead of a 12 volt power source to the starter housing.

NOTE: A battery charger set to the 12 volt/ 40 amp

range or a fully charged battery and a pair of jumper cables can be used.

Negative lead

Figure 6.3

4. Connect the positive lead to the cable stud on the starter.

• The starter should spin fast enough for the ben-

dix gear to slide out fully. If not, rebuild the starter.

• If the starter does not spin, repair or replace the

starter.

Positive lead

Rebuilding the starter

Brushes

Figure 6.4

Springs

Starter and Charging System

The starter motor used on the 4P90 engine is a permanent magnet dc motor with a radial commutator, similar to what is found in a repulser start motor. A radial commutator means that the commutator plates are perpendicular to the axis of the rotor.

With this arrangement, the brushes and brush holder are mounted to the end cap and the rotor will ride on top of them.

Stator housing

Figure 6.5

Starter motor disassembly:

1. Remove the starter by following the procedures described in the starter removal section of this chap ter.

2. Put alignment marks on the stator housing and the starter gear housing.

3. Put an alignment mark on the end cap and the st a tor housing.

NOTE: The starter will not work properly if the stator hous-

4. Remove the end cap using an 8 mm wrench.

See Figure 6.5.

ing is put on upside down. Vary the alignment marks to prevent this.

Figure 6.6

End cap

P90 Series Vertical Shaft Engines

5. Slide the stator housing off of the starter.

6. Pull the rotor out of the stator housing. NOTE: The rotor will be held to the stator by strong

magnets.

7. Inspect the rotor for signs of wear or damage.

Rotor

8. If the rotor is damaged, it may not be economically feasible to rebuild the starter.

9. Test the ro to r: 9a. Set the DMM to measure resistance (Ω scale). 9b. Measure the resistance across all of the com-

mutator plates.

• The reading should be less than 0.3 Ω.

9c. Test for continuity between the commutator

and the rotor shaft.

• The reading should read open line, over limit or

infinity depending on the meter used.

NOTE: If there is continuity between the comm u ta-

tor and the rotor shaft, the rotor is shorted. If the rotor is shorted it may not be economi cally feasible to rebuild the starter.

Commutator

Figure 6.7

10. Remove th e negative brushes by removing the two screws, indicated by the arrows in secure them to the end cap using a #2 phillips screwdriver.

11. Remove the brush holder and springs.

Figure 6.9., that

Figure 6.8

Figure 6.9

Seal

Figure 6.10

Washers

Nut

Starter and Charging System

12. Remove the nut and washers from the cable stud using a 10 mm wrench.

13. Remove the cable stud and the positive brushes.

14. Remove the insulator seal.

See Figure 6.10.

Figure 6.11

5/16” punch

15.Remove the bearing: 15a. Fill the bearing hole with grease. 15b. Insert a 5/16” pin punch. 15c. Tap the punch with a hammer to hydraulically

press the bearing out of the end cap.

NOTE: It may be necessary to add addition grease as the

bearing is being pressed out.

16. Remove the two screws, indicated by the arrows in Figure 6.12., from the underside of the starter gear housing using a #2 phillips screw driver.

NOTE: The screws were installed with a high strength

thread locking compound. It may be necessary to use a hand impact driver and/or heat to get the screws to release.

Figure 6.12

P90 Series Vertical Shaft Engines

17. Remove the scr ew, indicated by the arrow in Figure

6.13., from the topside of the starter gear housing using a #2 phillips screwdriver.

18. Separate the starter gear housing. See Figure 6.14.

Figure 6.13

19. Remove the pinion gear.

20. Remove the bendix gear assembly.

21. Remove the bushing from the starter gear housing. See Figure 6.15.

NOTE: A blind hole bearing puller with a 12mm

arbor or a screw extractor can be used.

Bendix gear

pinion gear

Figure 6.14

Screw extractor

Figure 6.15

Starter and Charging System

Screw extractor

Figure 6.16

rotor upper bearing

22. Remove the bushing from the clutch/pinion cover. See Figure 6.16.

NOTE: A blind hole bearing puller with a 11mm arbor or an

screw extractor can be used.

23. Drive the rotor up pe r bearin g ou t of th e clu tch /p inio n cover using a flat tipped punch.

See Figure 6.17.

Figure 6.17

P90 Series Vertical Shaft Engines

To re-assembly a starter motor:

1. Press the bushing into starter gear housing until there is 0.055” (1.4 mm) sticking out. See Figure 6.18.

0.055”

Figure 6.18

2. Press the rotor’s upper bearing into the clutch/pinion cover until it is flush with the cover.

3. Press the bushing into the clutch/pinion cover until it is flush.

See Figure 6.20.

See Figure 6.19.

Bearing

Figure 6.19

Bushing is flush with the casting

Figure 6.20

Starter and Charging System

Clutch/pinion gear assembly

Figure 6.21

Pinion gear

4. Insert the clutch/pinion gear assemb ly into the starter gear housing.

5. Install the pinion gear. See Figure 6.22.

See Figure 6.21.

clutch/pinion cove r

Figure 6.22

6. Mount the clutch/pinion cover to the starter gear housing.

NOTE: Apply a thread locking compound, such as Loc-

tite® 262, to the threads of the screws before installing them.

NOTE: The screw that lines up with the screw boss, indi-

cated by the arrow in Figure 6.23., is shorter than the other two screws.

Figure 6.23

P90 Series Vertical Shaft Engines

7. Clean the carbon from the commutator. NOTE: A pencil eraser is very effective in cleaning

commutators.

See Figure 6.24.

Figure 6.24

8. Insert the splined end of the rotor into the starter gear housing.

9. Slide the stator housing over the rotor assembly .

! CA UTION! CA UTION

will draw the stator up against the starter gear housing with great force.

See Figure 6.25.

Keep fingers clear while sliding the stator housing over the rotor. The magnets inside the stator housing

Rotor assembly

Figure 6.25

Alignment marks

10. Rotate the stator housing until the alignment marks (made before disassembly) line up. See Figure 6.26.

Figure 6.26

Bushing is flush with casting

Figure 6.27

positive brushes/cable stud assembly

Starter and Charging System

11. Press a new bushing into the end cap until it is flush with the casting.

12. Insert the seal into the end cap from the inside.

See Figure 6.27.

Seal

Figure 6.28

Insulator washer

Brush holder

13. Install the positive brushes/cable stud assembly.

14. Install the insulator washer. See Figure 6.28.

15. Install the flat washer against the insulator washer.

16. Install the lock washer.

17. Install the nut that retains the positive brushes/cable stud assembly.

18. Install the brush holder.

19. Insert the springs in the brush holder.

20. Install the negative brushes.

NOTE: The screws that anchor the negative brushes also

anchor the brush holder.

See Figure 6.29.

Figure 6.29

Negative brush

P90 Series Vertical Shaft Engines

NOTE: A special tool will be needed to compress

the brushes for assembly of the motor. See Figure 6.30.

To make the tool:

A. Cut a piece of sheet metal approximately

0.040” thick (19 or 20 gauge). B. Cut a slot in the metal, 5/8” wide x 1 5/8” long. C. Buff and debur all edges of the tool.

21. Insert the brushes into the brush holder. NOTE: The side of the brush with the copper wire

faces down in the brush holder.

1 5/8”

5/8”

Figure 6.30

This side faces down

2”

4.5”

NOTE: Insert the brushes one at a time. Sliding the

tool made earlier over them to press and hold them in place.

NOTE: It will take some force to compress all four

springs at once.

Figure 6.31

Figure 6.32

Figure 6.33

Starter and Charging System

22. Set the starter motor onto the end cap while keeping the brushes compressed into the brush holder. See Figure 6.33.

23. Carefully slide the brush holding tool out of the starter.

24. Rotate the end cap to line up the alig n me n t ma rks with the stator housing.

NOTE: Keep the starter motor compressed together.

25. Install the two screws that secure the end cap to the starter motor.

26. Bench test the starter before installing it on the engine.

P90 Series Vertical Shaft Engines

Charging system

The charging system used on MTD engines consists of a dual output alternator and a rectifier/regulator.

The charging system has a 5 amp AC output and a

3.75 amp DC output. The alternator consists of two parts; the rotor and the stator.

• Alternator rotor: The rotor consists of five magnets on the inside of the flywheel that rotate around a stator that is mounted to the cylinder block. As the crankshaft and flywheel rotate, the moving magnets induce a charge in the stator. See Figure 6.34.

Magnets

Figure 6.34

• Alternator stator field windings around an iron core. The stator is attached to the engine block beneath the flywheel. See Figure 6.35.

• Rectifier/regulator diodes that convert the AC current into DC current. The rectifier also has a regulator circuit built into it regulates the voltage to a specified range. See Figure 6.36.

: The stator consists of copper

: The rectifier is a set of four

Stator

Figure 6.35

Rectifier/regulator

Figure 6.36

Charging system testing

Starter and Charging System

To test the charging system:

Engine harness

connector

Figure 6.37

1. Locate the connection between the engine harness and the main harness of the machine. See Figure 6.37.

2. Start the engine and run it at full throttle.

3. Check the engine RPMs.

NOTE: The engine must be at 3,300 RPMs to test the

alternator output.

4. Connect the black (-) lead of a digital multimeter to a good ground on the engine.

5. Set the multimeter to read AC voltage.

6. Back probe the orange wire in the charger harness with the red (+) lead of the multimeter. See Figure 6.38.

Positive probe

Figure 6.38

Purple wire

7. The multimeter should read a voltage of 11 - 20 Vac.

NOTE: If the AC voltage is too low, remove the flywheel by

following the procedures described in Chapter 7: Ignition System and check the internal magnets. If they are still magnetic, replace the stator.

8. Set the multimeter read DC voltage.

9. Back probe the purple wire of the charger harness. See Figure 6.39.

NOTE: Will be a different color on the equipment side of

the harness connection.

10. The multimeter should read 13.75 - 15.5 Vdc.

Figure 6.39

P90 Series Vertical Shaft Engines

11. If the results do not match the specifications: 11a. Turn off the engine. 11b. Disconnect the regulator/rectifier. 11c. Start the engine again and run it at full throttle.

12. Set the multimeter to read AC voltage.

13. Connect the bla ck (-) lead of a digit al multimeter to a good ground on the engine.

14. Connect the red probe to one of the red wires from the stator harness.

NOTE: The meter should read 8.5 to 10 Vac.

See Figure 6.40.

15. Move the red probe to the other red wire.

NOTE: The meter should read 8.5 to 10 Vac. NOTE: If the meter shows the proper readings, the regulator/rectifier is bad and needs to be replaced. NOTE: If the readings don’t match what is listed above, check the flywheel magnets. If the magnet are still

magnetic, replace the stator.

Figure 6.40

Stator

Starter and Charging System

To remove/replace the stator:

1. Remove and ground the spark plug wire.

2. Remove the flywhe el by following the steps described in Chapter 7: Ignition System.

3. Remove the starter by following the procedures described in the starter section of this chapter.

4. Remove the two screws, indicated by the arrows in Figure 6.41., that secure the stator with a 10mm wrench.

Figure 6.41

5. Remove the two screws, indicated by the arrows in Figure 6.42., that hold the baffle to the engine block using a 10 mm wrench.

Figure 6.42

Old style

New style

Figure 6.43

6. Slide the baffle off of the engine.

7. Disconnect the stator harness from the afterfire solenoid.

8. Disconnect the stator harness from the ignition module.

9. Disconnect the stator harness from the regulator/rectifer.

10. Remove the stator assembly.

11. Install the stator by following the above steps in reverse order.

NOTE: Early production engines have a simple bullet con-

NOTE: All service replacement stators and afterfire sole-

noids will be shipped with an adaptor and an instruction sheet on how to use the adaptor, if needed.

12. Test run the engine in a safe area and retest the voltage output before returning to service.

See Figure 6.43.

P90 Series Vertical Shaft Engines

Rotor

Rotor failures are extremely rare. To check the rotor:

• Confirm that the magnets are firmly attached to the flywheel.

• Hold a screwdriver or a similar tool made of ferrous metal within a 1/4” of each magnet.

• If the tool is drawn to the magnet, the rotor is good.

Figure 6.44

Chapter 6: Specification Table

Description Specification

Flywheel nut 74 - 85 ft lbs (100 - 115Nm) Alternator stator screws

80 - 106 in lbs (9 - 12 Nm) Starter mounting screws 195 - 221 in lbs (9 - 12Nm) AC output 11 - 20 Vac @ 3,300 RPM DC output 13.75 - 15.5 Vdc @ 3,300 RPM Starter armature resistence <0.2Ω Alternator stator resistence 0.5 - 1.0Ω

Troubleshooting the ignition system

Spark tester

CHAPTER 7: IGNITION SYSTEM

The purpose of the ignition system is to provide a spark in the combustion chamber at the proper time to efficiently ignite the fuel/air mixture. The steps in troubleshooti ng the ignition system are:

1. Examine the spark plug(s) by following the steps described in the spark plug section of this chapter.

NOTE: It is convenient to check the compre ssion when the

spark plug is removed for examination.

2. Connect a spark tester between the spark plug wire and a good ground point on the engine. See Figure 7.1.

NOTE: Do not connect the spark tester to the spark plug

when testing for ignition.

Ignition System

Never remove the spark plug and

! CAUTION! CAUTION

Figure 7.1

ing out of the spark plug hole will catch on fire.

NOTE: It only takes 1,000 volts to jump a 0.025” a ir gap in o pen atmo sp her e, it takes 10,000 volts to jump the

same gap at 120 psi; therefore, an open air spark test is not valid.

NOTE: The spark should be a minimum of 10 Kv (10,000 volts) at pull over speed.

3. Move the throttle lever to the full throttle position.

4. Turn the ignition key to the start position. If sparks can be seen in the spark tester, the ignition system is working.

NOTE: If there are sparks present in the spark tester, install a known-good spark plug and prime test the

engine. If the engine does not start, check the fly wheel key. If the fly wheel key is intact, the problem is not in the ignition system. Check the engine’s compression.

5. If no sparks or weak sparks are seen in the spark tester, check the module air gap. NOTE: If the module air gap is correct, further testing is required.

6. Unplug the wire that connects the ignition module prim ary winding s to a gr ound for engine shut d own (the connector is behind the dipstick tube).

7. Re-test for sparks.

• If ther e ar e no sparks, the mod u le is bad or th e flywheel magnets have lost their magnetism (very rare).

hold it against the cylinder head to test for spark. The fuel/air mix com-

• If there are sparks, troubleshoot the electrical system of the equipment that the engine is mounted to.

P90 Series Vertical Shaft Engines

The module

The coil in this ignition system is an inductive discharge magneto, contained in a single module.

• The inductive discharge module has a two leg design.

• The module is energized by the passing of a magnet mounted in the flywheel.

• Ignition timing is set by the location of the flywheel in relation to the crankshaft. Proper timing is maintained by a steel key.

Normal performance of the coil is to produce at least 10,000 volts at start-up speed. The presence or absence of strong spark, with the ignition switch disconnected , is genera lly enough to ide ntify the

ignition coil as good or bad. Resistance readings may help confirm the source of the failure, but are generally meaningless because they only measure a small part of the module .

NOTE: No spark or a weak spark may be the result of an improper air gap. The air gap space should be

0.016”-0.024” (0.4 - 0.6mm).

Simple spark-testers are readily available a nd inexpe nsive. Thexto n Part # 404 is available from a variety of retailers, and similar tools are available from other manufacturers. See Figure 7.2.

Instructions on back of package

Figure 7.2

NOTE: If the complaint is that the engine quits running when it gets hot, the ignition module should be tested

with the engine at normal operating temperature.

NOTE: An in line spark tester can be used between the spark plug and the sp ark plug wire. Run the engine

until it starts to quit and check the spark tester for spar ks to determine if this is an ignition or carburetion issue.

• At operating speed, the ignition should produce voltage approaching 12,000.

• At start up speed (~ NOTE: The voltage required for a flash-over will vary with spark plug condition and gap.

600 RPM), voltage should be at least 10,000V.

NOTE: Failure of the magnets in the flywheel is exceedingly rare. To test the magnets, simply hold an item

made of ferrous metal roughly 1/4” (0.635cm) away from the magnets in the flywheel. It should be drawn to the flywheel. A wrench or screwdriver is suitable for this test.

Module removal

Ignition System

1. Unplug the spark plug.

Afterfire solenoid lead

Module wire

Figure 7.3

2. Remove the blowe r/air filter housing by following the steps procedures in Chapter 3: Air Intake System.

3. Disconnect the module wire that goes to the system harness.

4. Remove the module using a 10 mm wrench.

NOTE: The engine model number is on the module. When

See Figure 7.3.

installing a new module, make sure the model numbers match.

See Figure 7.4.

Engine model number

Figure 7.4

P90 Series Vertical Shaft Engines

Installing the module and setting the air gap

NOTE: If just setting the air gap, loosen the module

mounting screws first then follow the proce dures described below.

1. Rotate the flywheel so that the magnets are away from where the module is mounted.

2. Install the module. Do not tighten the module screws.

3. Place a non-ferrous feeler gauge between the module and the flywheel.

NOTE: The air gap should be 0.016” - 0.024” (0.4-

0.6 mm).

4. Rotate the flywheel so that the magnets align with the legs of the module while holding the feeler gauge in place.

5. Tighten the module mounting screws to a torque of 80 - 106 in-lbs (9 - 12 Nm).

6. Rotate the flywheel to remove the feeler gauge.

7. Connect the module lead to the system harness.

8. Connect the spark plug wire to the spark plug.

See Figure 7.5.

Plastic feeler gauge

Figure 7.5

9. Install the blower/air filter housing.

10. Test run the engine before returning to service.

Ignition System

Flywheel

The flywheel holds the magnets. These magnets induce a field in the module which in tu rn produces a spark. It also controls the timing of the ignition system by controlling when the magnets are introduced to the module.

A sheared flywheel key will throw off the ignition timing. Sheared keys are uncommon on MTD engines. If one is found, check the crankshaft and flywheel for damage.

To Remove and/or inspect the flywheel and key:

1. Remove the blower/air filter housing by following the

Harmonic balance puller

steps procedures in Chapter 3: Air Intake System.

2. Remove the ignitio n module by following the procedures described in the module sectio n of this chapter.

3. Block the piston to prevent the crankshaft from turning by:

3a. Remove the spark plug. 3b. Insert approximately 3.3’ (1 m) of st arter rope in

the spark plug hole.

NOTE: Leave part of the rope stic king out of the engine so

that the rope can be removed later.

- or 3c. Use a strap wrench to hold the flywheel.

Figure 7.6

If the flywheel shows any signs of physical damage such as cracks, broken vanes (if equipped),

! CA UTION! CA UTION

6. Inspect the key, keyway, and tapered mating surfaces of the flywheel and crankshaft.

NOTE: If the key is damaged, the crankshaft must be replaced. NOTE: On installation, confirm that the key is properly seated (the flat of the key parallel with the threaded

or a damaged keyway, replace it. A damaged flywheel poses a threat of a burst failure. Burst failures are extremely hazardous to surrounding people and property.

section of the crankshaft) in the keyway, and that the tapers are fully seated. Key or keyway failure may result from improper seating.

4. Remove the flywheel nut, using a 23mm wrench.

NOTE: The three screws needed for the puller are 6mm x

1.0, 60mm in length or longer depending on the puller used.

5. Remove the flywheel by using a harmonic balancer puller.

See Figure 7.6.

NOTE: It is not necessary to remove the plastic fan and

support washer to install the puller.

NOTE: Never strike the crankshaft with a hammer.

IMPORTANT: The tapers in flywheel and on the crankshaft must be clean and dry. The flywheel is held in

place by the friction between the flywheel and the crankshaft, not the key. The key is only to guide the flywheel to the proper position until it is torqued down.

7. Install the flywheel nut to a torque of 81 - 85 ft-lbs (110 - 115 Nm ).

8. Install the module by following the procedures described in the module section of this chapter.

9. Reassemble the engine.

10. Test run the engine before returning to service.

P90 Series Vertical Shaft Engines

Spark plug

• The spark plug is a F6RTC, part #951-10292, gapped to 0.024” - 0.031” (0.6 - 0.8 mm).

• Wear rate will vary somewhat with severity of use. If the edges of the center electrode are rounded-off, or any other apparent wear / damage occurs, replace the spark plug before operating failure (no start) occurs.

Cleaning the spark plug

• Cleaning the spark plug is not recommended. If the plug needs to be cleaned, replace it.

• Use of a wire brush may leave metal deposits on the insulator that cause the spark plug to short-out and fail to spark.

• Use of abrasive blast for cleaning may damage the ceramic insulator or leave blast media in the recesses of the spark plug. When the media comes loose during engine operation, severe and non-warrantable engine damage may result.

Inspection of the spark plug

Inspection of the spark plug can provide indications of th e op er a ting con d ition of th e en gin e .

• Light tan colored deposits on insulator and electrodes is normal.

• Dry, black deposits on the insulator and electrod es indicate an over-rich fuel / air mixture (too much fuel or not enough air)

• Wet, black deposits on the insulator and electrodes indicate the presence of oil in the combustion chamber.

• Heat damage (melted electrodes / cracked insulator / metal transfer deposits) may indicate detonation.

• A spark plug that is wet with fuel indicates that fuel is present in the combustion chamber, but it is not being ignited.

Spark plug removal

1. Disconnect and ground the spark plug wire. See Figure 7.7.

2. Remove the spark plug using a 13/16” or 21mm wrench.

3. Gap a new spark plug to 0.024” - 0.031” (0.6 - 0.8 mm).

4. Install the new spark plug and tighten to a torque of 15 - 18 ft - lbs (20 - 25 Nm).

Spark plug

wire

Figure 7.7

Exhaust

CHAPTER 8: EXHAUST

The exhaust system is a frequently overlooked component of an engine. It is important to make sure the muffler

is in good condition and free of debris and/or insects.

NOTE: A blocked muffler will result in poor performance. If a muff ler is completely blocked, the engine may not

start.

Spark arrestor (if eq uipped)

A spark arrestor , part #951-12329, is available as an option.

NOTE: Spark arr estors are an option that are required on

all engines used in California and U.S. national parks.

See Figure 8.1.

The spark arrestor also serves to keep blockages out of the exhaust system.

NOTE: T ypical blockages include insect nest s built during

the dormant season.

Figure 8.1

Figure 8.2

Spark arrestor

The spark arrestor should be checked and/or cleaned every month. The spark arrestor can be inspected by shin ing a flash light into the muffler. See Figure 8.1.

If the spark arrestor needs to be cleaned or replaced:

1. Allow the engine to cool.

2. Remove the four screws, indicated by the arrows in Figure 8.2. that retain the muffler shield using a 10mm wrench and lift it off of the engine.

3. Lift the muffler shield off of the engine.

4. Remove the spark arrestor retaining screw using a #2 phillips screwdriver.

5. Pull the spark arrestor out of the muffler.

6. The spark arrestor can be:

•Replaced

• Cleaned by mechanical means

• Solvent cleaned

• Burned clean using a butane or propane torch.

7. Install the spark arrestor by following steps 1-3 in reverse order.

P90 Series Vertical Shaft Engines

Muffler removal/replacement

1. Remove the four screws, indicated by the arrows in Figure 8.2. that retain the muffler shield using a 10mm wrench and lift it off of the engine.

2. Lift the muffler shield off of the engine.

3. Remove the screw, indicated by the arrow in Figure

8.4. that secures the rear of the muffler to the engine block using a 10mm wrench.

Figure 8.3

4. Remove the two nuts that hold the manifold pipe to the cylinder head using a 13mm wrench. See Figure 8.4.

5. Slide the muffler and man ifold pipe off of the engine. NOTE: The muffler and the manifold pipe are ser-

viced as one assembly on the 4P90 service of engines.

Figure 8.4

Manifold pipe

Figure 8.5

Remove all gasket material

Figure 8.6

Exhaust

6. Clean all of the gasket material off of the cylinder head and the muffler.

NOTE: The MTD engine uses a graphite exhaust gasket.

It is not reusable and must be replaced every time the muffler nuts are loosened.

NOTE: The graphite exhaust gasket transfers heat from

the cylinder head to the muffler. The heat transfer helps to keep the engine operating temperature under control. Do not substitute an exhaust gaske t made from another material.

7. Install the muffler by following the previous steps in reverse order.

NOTE: Tighten the manifold nuts to a torque of 22 - 26 ft-

lbs (30 - 35 Nm).

8. Test run the engine before returning to service.

See Figure 8.6.

P90 Series Vertical Shaft Engines

Catalytic converter

On engines equipped with a catalytic converter muffler, there is an air injector assembly on the cylinder head, as show in injector to the exhaust port.

When the exhaust valve is open the gases inside the engine escape to the muffler at great velocity. The pres sure of the exhaust gases will close the reed valve in the air injector, preventing them from escaping through the injector. The exhaust gases are forced through the cata lyst, which will chemically change the gases to lower the emissions.

Figure 8.7. There is a passage from the air

When the exhaust valve closes, the momentum of the gases keep them flowing out of the muffler. This will create a low pressure in the exhaust port. The low pressure will cause fresh air to be drawn in through the air injector. The fresh air is needed to re-charge the catalyst for the next exhaust cycle.

NOTE: The catalytic converter is part of the muffler and can not be serviced separately.

To service the air injector:

NOTE: The air injector red valve can become plugged up from dirt, grass, insects and many other things. This

would prevent fresh air from getting to the converter.

1. Remove the two screws that hold reed valve assembly to the cylinder head using a #2 phillips screwdriver.

See Figure 8.7.

2. Clean the reed valve as needed.

3. Install the reed valve.

4. Test run the en gin e befo r e re tur n ing it to serv ice.

Air injector

Figure 8.7

Cylinder head removal

Cylinder head

CHAPTER 9: CYLINDER HEAD

The Cylinder head of the MTD engine can be removed without removing the engine from the piece of equipment.

To remove the cylinder head:

1. Disconnect and ground the spark plug high tension lead.

2. Remove the blower/air filter housing, carburetor and insulator plate by following the steps described in Chapter 3: Air Intake System.

NOTE: The fuel line and the linkages can be left attached

to the carburetor.

NOTE: If the fuel line is disconnected from the carburetor,

the line must be discarded and new fuel line used when the carburetor is installed.

Figure 9.1

Ground lead

Figure 9.2

3. Disconnect the afterfire solenoid’s ground lead using an 8 mm wrench.

4. Remove the screw that attaches the baffle to the bottom of the head using an 8 mm wrench.

5. Remove the muffler and heat shield by following the steps described in Chapter 8: Exhaust.

See Figure 9.2.

P90 Series Vertical Shaft Engines

6. Remove the two screws, indicated by the arrows in Figure 9.3, that secure the baffle to the cylinder using an 8 mm wrench.

7. Remove the baffle.

8. Remove the spark plug using a 13/16” or 21mm wrench.

Figure 9.3

9. Rotate the crankshaft until it is at TDC of the compression stroke by following the steps described in the valve lash section of Chapter 1: Introduction.

10. Remove the four screws securing the valve cover using a 10mm wrench.

11. Loosen the jam nuts and fulcrum nuts that secure the rocker arms using a 10mm wrench and a 14mm wrench.

12. Pivot the rocker arms aside, or remove them completely, and remove the push rods.

NOTE: Once broken-in, the rocker arm should be

kept with its corresponding valve.

NOTE: The intake and exhaust push rods are iden-

tical and interchangeable. It is preferable, but not absolutely necessary, to return the same push rods to their original locations on engine with substantial ( ing time.

See Figure 9.4.

>100 hours) operat-

Valve cover

Figure 9.4

Jam nut

Fulcrum nut

13. Remove the head bolts using a 14 mm wrench.

Figure 9.5

Cylinder head

surface

Sealing surface

Figure 9.6

14. Lift the cylinder head off of the engine.

15. Carefully clean all sealing surfaces of all gasket residue. Do not scratch the sealing surfaces. See Figure 9.6.

NOTE: If replacing the head, double-nut and remove the

exhaust studs.

NOTE: Make a visual inspection of the valves and cylinder

bore to confirm the initial diagnosis.

P90 Series Vertical Shaft Engines

Cylinder head installation

1. Place a new head gasket on the cylinder, allowing the alignment dowels to hold it in place. See Figure 9.7.

NOTE: The 4P90 series of engines use a metal

head gasket with rubber seals.

Dowel pins

Figure 9.7

2. Position the cylinder head on the engine block.

3. Install the 4 head bolts, and tighten them to a step torque of 41 - 44 ft lbs. (55 - 60 Nm) in an alterna ting diagonal pattern.

NOTE: The bolt closest to the exhaust valve must

be the last bolt tightened. Failure to do so can result in the head bolt loosening up.

NOTE: The head bolts have a self locking thread

form.

4. Insert the push rods.

5. Install the rocker arms.

6. Adjust the valve lash by following the steps described in Chapter 1: Introduction.

7. Install the baffle.

8. Install the muffler by following the steps described in Chapter 8: Exhaust.

9. Install the carburetor and engine shroud, usin g new gaskets, by followin g the steps de scribed in Ch apter 3: Air Intake

10. Test run the equipment in a safe area bef or e returning it to service. Check all safety features.

See Figure 9.8.

Exhaust

port

Figure 9.8

Cylinder head

Valves

The valves and valve seats can be serviced by grinding and lapping or the head can be replaced. Depending on local machine and labor costs, it is probably more economical to replace the cylinder head versus servicing the valves.

To service the valves: NOTE: Servicing valves during the warranty period will

Valve adjusters

1. Remove the cylinder head by following the steps

2. Remove the rocker arms by:

3. Remove the valve adjusters. See Figure 9.9.

void the warranty. Warranty valve repairs are to be accomplished by replacing the cylinder head.

described earlier in this chapter.

2a. Remove the jam nuts. 2b. Remove the fulcrum nut. 2c. Slid e th e ro cke r ar ms off of the rocker stud s.

Figure 9.9

Valve keeper

Figure 9.10

NOTE: It may be necessary to press down on the valve

retainers to unseat the adjusters.

4. Remove the valve retainers by applying light finger pressure and moving the retainer so that the valve stem passes through the large part of the “keyhole” opening in the retainer.

NOTE: The valve keepers are not interchangeable. NOTE: If the engine has a dropped valve, remove the cyl-

inder head, inspect the valve and the piston for damage.

See Figure 9.10.

P90 Series Vertical Shaft Engines

5. Lift the springs off of the valve stems.

6. Slide the valves out of the cylinder head. NOTE: Only the intake valve has a va lve guide seal.

See Figure 9.11.

7. Inspect the valve seat. See Figure 9.12.

Seal

Figure 9.11

• Valve seats are 45 degrees, with a 25 degree

topping cut and a 60 degree narrowing cut.

• Seat width should be 0.028” - 0.035” (0.7 -

0.9mm) with a margin of 0.049” - 0.061 (1.25 -

1.55 mm) on the exhaust valve and 0.027” (1mm) on the intake valve.

NOTE: The valve seat can be ground to clean it up

as long as the finished seat is within the tol erances listed above.

8. Inspect the valve stem. See Figure 9.13.

9. Inspect the valve springs. NOTE: Valve spring free length should be at least

1.2” (30.5mm). Original length is 1.54” (39mm).

10. Install the valves in the cylinder head by following steps 2 - 5 in reverse order.

0.028 - 0.035”

Seat angle is 45

margin

Seat contact

Figure 9.12

Inspect for a

burnt edge

Figure 9.13

Cylinder head

11. Test the valves for leaks by: 11a. Place the cylinder head on a couple of wood blocks with th e valv es facing up. 11b. Pour a small amount of gasoline or parts cleaning solvent into the combustion chamber (just enough to

cover the valves). 11c. Le t th e cylinde r he a d sit for ten minu tes. 11d. Check for gasoline leaking out of the intake and exhaust ports.

12. Install the cylinder head by following the steps described earlier in this chapter.

13. Set the valve lash by following the steps described in Chapter 1: Introduction.

14. Test run the engine in a safe area before retu r ning it to ser vice. Check all safety features.

P90 Series Vertical Shaft Engines

Push rod guide plate

The push rods move through a guide plate that aligns the push rods with the rocker arms. The guide plate also

acts as a bushing for the push rods. Over time, the guide plate will wear out and need to be replaced.

NOTE: A guide plate that is worn out can allow the push rod to slip out from under the rocker arm. When that

happens, the push rod will side load the rocker arm, breaking the rocker arm stud.

To service the push rod guide plate:

1. Remove the valve cover.

2. Disconnect and ground the spark plug wire.

3. Remove the spark plug.

4. Rotate the engine to TDC of the compression stroke.

See Figure 9.14.

5. Remove the rocker arm jam nuts using a 10 mm wrench while holding the fulcrum nuts with a 14 mm wrench.

6. Remove the fulcrum nuts and the rocker arms.

7. Remove the push rods.

8. Remove the rocker arm studs and the guide plate using a 14mm wrench

9. install the guide plate by following the previous steps in reverse order.

NOTE: Tighten the rocker studs to a torque of 195 -

221 in lbs (22 - 25 Nm).

Probe for TDC

Fulcrum nit

Jam nut

Figure 9.14

10. Adjust the valve lash by following the procedures described in Chapter 1: Introduction.

11. Test run the equipment in a safe area before returning it to service.

Figure 9.15

Crankshaft, piston and connecting rod

CHAPTER 10: CRANKSHAFT, PISTON AND CONNECTING ROD

The exact procedure a technician uses to disassemble an engine depends on the type of repairs needed. This chapter is written as a set of procedures that should provide the user with sufficient information to complete any fea sible repair to the engine short block assembly.

The instructions are written with the assumption that the engine has been removed from the equipment. These are bench work instructions.

1. Drain and save the oil from the engine by following the steps described in Chapter 1: Introduction.

2. Remove the blower/air filter housing and carburetor by following the steps described in Chapter 3: Air Intake

System.

3. Remove the starter by following the steps described in Chapter 6: Starter and Charging System.

4. Remove the flywheel and ignition module by following the steps described in Chapter 7: Ignition system.

5. Remove the muffler by following the steps described in Chapter 8: Exhaust.

6. Remove the cylinder head by following the steps described in Chapter 9: Cylinder Head.

7. Remove the dipstick tube.

8. Remove the crank case cover bolts using a 12mm wrench.

9. Carefully slide the crank case cover off of the crank shaft.

10. Remove the thrust washer. See Figure 10.1.

Thrust washer

Figure 10.1

P90 Series Vertical Shaft Engines

11. Align the timing marks on the cam and the crankshaft to allow easier removal of the cam and to help protect the compression relief from damage. See Figure 10.2.

NOTE: The timing marks were filled in with red paint

for the picture.

12. Remove th e camshaft.

13. Remove the balance shaft. See Figure 10.3.

Timing marks

Figure 10.2

Remove the balance shaft

Cam shaft

Compression relief

NOTE: The valve tappets should be kept riding

against their original lobes. Once broken in, switching the tappets to run on different cam lobes will cause rapid tappet and cam wear.

14. Remove the valve tappets. See Figure 10.4.

Figure 10.3

Valve tappets

Figure 10.4

Remove the connecting rod bolts

Figure 10.5

Crankshaft, piston and connecting rod

15. Match mark the connecting rod and cap.

16. Remove the connecting rod cap using a 10mm wrench.

NOTE: Rotating the crank shaft after the connecting rod

See Figure 10.5.

bolts are removed will help to separate the con necting rod from the cap.

Remove one of the

piston pin retainers

Figure 10.6

17. Push the piston out of the cylinder.

NOTE: Sometimes a ridge of carbon builds up where the

cylinder meets the head. If this happens, the piston can be removed from inside of the cylinder block.

18. Remove one of the piston pin retaining rings. See Figure 10.6.

19. Remove the piston pin.

20. Remove the piston rings from the piston using a pair of piston ring pliers.

NOTE: The piston, rings and connecting rod are currently

not available as service parts. If they are damaged or worn, the engine must be short blocked.

See Figure 10.7.

Figure 10.7

21. Remove the crankshaft.

NOTE: The crankshaft bearings are pressed onto the

crankshaft and will come out with it.

Piston ring pliers

P90 Series Vertical Shaft Engines

Crankshaft inspection

1. Inspect the crankshaft journals and the cra nk pin for galling, scoring, pitting or any other form of damage.

NOTE: This is mostly a visual check. Measurement

is to determine if it is within the specifications after it is found to be OK visually.

NOTE: The crankshaft and bearing are serviced as

one assembly.

2. Measure the crank pin where the connecting rod attaches to the crankshaft using a vernier caliper or a micrometer.

NOTE: Micrometers are the preferred way to mea-

3. Check the crankshaft for straightness by measuring the run out. The crankshaft run out can be checked by:

See Figure 10.8.

sure the journals. Measure the center and the ends to check for tapering or egging.

micrometer

Crank pin

Figure 10.8

3a. Place the crankshaft on a pair of matched V-blocks or in the engine block with the sump installed. 3b. Place a dial indicator at a smooth point at either end of the crank shaft. 3c. Slowly turn the crank shaft while watching the dial indicator. NOTE: Stop the crank shaft before the dial indicator hits the keyway. 3d. Compare the reading on the dial indicator to th e specification listed at the end of this chapter. 3e. Repeat the above steps on the other end of the crank shaft.

Cub Cadet MTD P90 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

CHAPTER 1: INTRODUCTION

Professional Service Manual Intent

Safety

Fasteners

Assembly instructions

Model and serial number

Maintenance

Spark plugs

Air filter

Oil type and capacity

Changing the oil

Oil filter

Oil pre-screen

Fuel system

Servicing the fuel system

Fuel filter

Valve lash

Exhaust system

Cleaning the engine

General torque specifications

CHAPTER 2: BASIC TROUBLESHOOTING

Definitions

Introduction

Steps to troubleshooting

Define the problem

Identify factors that could cause the problem

Repairing the problem

Prime test

Leak-down test

Compression test

PCV testing

Air filter

CHAPTER 3: AIR INTAKE SYSTEM

Blower/air filter housing

Carburetor and Insulator

CHAPTER 4: THE FUEL SYSTEM AND GOVERNOR

Inspecting the fuel

Test fuel for alcohol

Choke/throttle cable adjustment

Carburetors

Inspecting the carburetor

Disassembly and rebuilding the carburetor

Engine speed adjustment

Afterfire solenoid

Testing the afterfire solenoid

Governor

Governor arm

Governor shaft

Governor cup and the governor gear

CHAPTER 5: LUBRICATION

Oil type and quantity

Oil dipstick

Dip stick tube removal

Lubrication system

Testing the oil Pump

Positive crankcase ventilation valve

Starter removal

CHAPTER 6: STARTER AND CHARGING SYSTEMS

Bench testing the electric starter

Rebuilding the starter

Charging system

Charging system testing

Stator

Rotor

Troubleshooting the ignition system

CHAPTER 7: IGNITION SYSTEM

The module

Module removal

Installing the module and setting the air gap

Flywheel

Spark plug

Cleaning the spark plug

Inspection of the spark plug

Spark plug removal

CHAPTER 8: EXHAUST

Spark arrestor (if eq uipped)