Troy-Bilt 78, 83, 90 User Manual

For Parts Call 606-678-9623 or 606-561-4983

Professional Shop Manual

78/83/90 Series Horizontal Shaft Engines

(277/357/420 cc 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.

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Table of Contents

Chapter 1: Introduction

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

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

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

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

Model and serial number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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

Air filter (summer engines) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Oil type and capacity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Changing the oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Fuel filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Valve lash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Cleaning the engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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

Maintenance Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Frequently used specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Chapter 2: Basic Troubleshooting

Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Steps to troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Define the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Identify factors that could cause the problem . . . . . . . . . . . . . . . . . . . . . . . . 18

Repairing the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Prime test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Leak-down test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Compression test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

PCV testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Chapter 3: Air Intake systems

Heat box (snow engines) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Air filter (summer engines) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Air filter base and control panel (summer engines) . . . . . . . . . . . . . . . . . . . 32

Carburetor and Insulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

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Chapter 4: The Fuel System and Governor

Inspecting the fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Test fuel for alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Fuel tank vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

The fuel filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Inspect the fuel lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

The fuel tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Evaporative (EVAP) emissions system . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

Troubleshooting the EVAP System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

Charcoal canister . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Roll over valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Choke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Primers (snow engines) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Carburetors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Inspecting the carburetor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Disassembly and rebuilding of the carburetor . . . . . . . . . . . . . . . . . . . . . . .52

Fuel shut-off valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Governor arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Governor shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Governor cup and the governor gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Governor adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Chapter 5: Lubrication

Oil type and quantity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Oil dip stick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Dip stick tube removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Lubrication system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Positive crankcase ventilation valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Chapter 6: Starter and Charging Systems

Recoil Starter Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Starter Cup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Starter Rope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Starter pulley and recoil spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Electric starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Charging system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Charging system testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Stator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

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Chapter 7: Ignition System

Troubleshooting the ignition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Stop switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

Remote (ignition) stop switch (snow engines) . . . . . . . . . . . . . . . . . . . . . . . 83

Test for ignition that won’t turn off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

The module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Module removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Installing the module and setting the air gap . . . . . . . . . . . . . . . . . . . . . . . . 87

Flywheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

About the spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Cleaning the spark plug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Inspection of the spark plug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Spark plug removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Chapter 8: Exhaust

Summer engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Spark arrestor (if equipped) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Muffler removal/replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Muffler removal/replacement (snow engines) . . . . . . . . . . . . . . . . . . . . . . . . 94

Chapter 9: Cylinder Head

Cylinder head removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Cylinder head installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Chapter 10: Crankshaft, piston and Connecting Rod

Crankshaft inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Piston Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109

Connecting rod inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Cylinder inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Balance Shaft (483 & 490) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Engine specifications chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Engine torque values chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

Chapter 11: Failure Analysis

Abrasive Ingestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Insufficient lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Engine Overspeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Overheated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Mechanical Breakage/ Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Detonation/preignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

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III

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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 78/83/90 series MTD horizontal 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 RNI NG! WA RNI NG

! 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 pro cedures 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 Suppor t.

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.

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78/83/90 Series Horizontal 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.

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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 summa- rized 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 pr ocedures. Th is avoids repeating the same procedure two or three times in the manual.

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78/83/90 Series Horizontal Shaft Engines

Model and serial number

The model and serial number can be found on a white sticker with a bar code. The sticker is located on the right side of the engine at the bottom of the block. See Figure 1.1.

NOTE: The serial number will always start with the

model number.

MTD H oriz ontal Engine Model Desi gna tors

Front of engine

Model /serial number

Figure 1.1

Starter/Alternators

1=Recoil st art 2=Electric start 3=E. start/alt. 20W/20W 4=E. start/alt. 3A DC/5A

Bore Dia. (mm)

MTDEngineSerialNumbers

1P65FH/0510271A0023

1 6 1 - S H A

Major Revision Change

Compliance

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

End Product

C Chipper/Shredder J Snow/No tank L L ogsplitter R T iller (slow reverse) SSnow T Tiller V Verticutter

Modelnu m b er

Mont hYea r

ProducingLine #

Date

Engi ne number

A=1stshift

sh i f t

B=2

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Maintenance

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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 failures 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 gapped to 0.026” - 0.030” (0.65 - 0.75 mm). See Figure 1.2.

Introduction

Figure 1.2

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 befo re operating failure (no start) occurs.

3. Cleaning the spark plug: 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 c on di tion of th e en gine .

• Light tan colored deposits on insulator and electrode s is nor mal.

• Dry , black deposits on the insulator and electrodes 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.

NOTE: The F6RTC plug is the only plug that is EPA certi-

fied for the MTD engine.

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78/83/90 Series Horizontal Shaft Engines

Air filter (summer engines)

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.

NOTE: Snow engines do not have air filters

because the snow will plug up the filter . Gen erally the air is clean enough that there is minimal risk of dirt ingestion when the ground is covered with snow.

2. Air filters used on the MTD engine are designed to

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

3. The filter should be checked on a regular basis pos-

sibly several times in a season.

4. Typically an air filter should be changed before every season.

5. If a foam air pre-cleaner is dirty, but not in bad of condition it can be cleaned and reused. The paper pleate d fil-

ters can be shaken or lightly tapped to free the debris from the filter. 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.

Paper-pleated element

Foam pre-filter

Figure 1.3

6. Foam pre-filters can be washed in warm soapy water.

NOTE: When drying a foam filter either squeeze it in side 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.

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Introduction

Oil type and capacity

MTD engines use oil with a SF/SG API rating or better is the recommended oil for this engine. The winter engines use SAE 5W-30 oil and the summer engines use SAE 10W-30 oil. The oil capacity for all of the 78/83/90 series engines is 37 fl.oz (1.1 liters).

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

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

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 microscope 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.

NOTE: There are two types of dip sticks that can be found

on MTD engines; a threaded dip stick that was used on older engines and a quarter turn dip stick that is used on engines currently being produced. See Figure 1.4.

1/4 turn

Figure 1.4

Threaded

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To check the oil with a threaded dip stick:

1. Twist and remove the dip stick from the engine.

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

3. Re-insert the dipstick without threading it in to get the oil level reading.

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

To check the oil with a 1/4 turn dip stick:

1. Twist and remove the dip stick from the engine.

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

See Figure 1.5.

Do not thread dipstick in to check the oil level

Figure 1.5

Fully seat the dip stick before reading it

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 lowest point on the dipstick that is completely covered with oil.

Changing the oil

NOTE: If the engine has been running, allow the

engine to cool before doing any mainte nance work.

NOTE: The oil should be changed after the first 5 hours of operation and every 50 hours there after.

1. Place a suitable drain pan under the drain plug to collect the oil.

2. Drain the oil by removing the drain plug located at the end of the extension pipe threaded into the base of the engine, using a 10mm wrench. See Figure 1.7.

3. When all of the oil has drained out, reinstall the drain plug. Tigh te n the d rain p l ug to a torq ue of 1 06124 in-lbs (12-14 Nm).

See Figure 1.6.

Figure 1.6

Oil drain

4. Fill the engine with 37 fl.oz (1.1 liters) of fresh, clean oil that is the appropriate weight for the application.

5. Safely dispose of the used oil according to the local laws and regulations.

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Figure 1.7

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Introduction

Fuel

Gasolines currently on the market are not pur e gasoline. Today’s fuels have alcohol and other additives in them to reduce emissions. The fuel make up can vary seasonally and geographically.

Fuel with alcohol added to it is sometimes referred to as “oxygenated fuel”. The extra oxygen carried by the ethanol increases the oxidation of the fuel. This speeds up the process that causes the fuel to go bad.

Excessive alcohol in fuel creates a lot of problems for gasoline engines. One of the biggest problems is that alcohol attracts and holds water. This corrodes the metal components of the fuel system, especially the carburetor. Alcohol also does not produce as much heat as gasoline when burnt. This results in less power for the en gine.

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

NOTE: E85 and E20 fuels are not to be used in any MTD engines. NOTE: Use clean, fresh fuel with a pump octane rating of 87 or greater.

• Stale or out-of-date fuel is the leading cause of hard starting issues.

• In areas that have high amounts of alcohol in their fuel, high oct ane fuel may imp rove engine performance and startability.

Fuel filters

fuel filter

Nipple

Figure 1.8

Dirty fuel can clog the carburetor and introduce abrasive materials into the engine. To help prevent that, MTD engines are equipped with a fuel filter . The fuel filter is p art of the fuel tank nipple.

See Figure 1.8.

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To replace the fuel filter:

To avoid personal injury or property

! WARN IN G! WARN IN G

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.

1. Siphon the fuel out of the fuel tank.

2. Remove the front fuel tank shroud using a 10 mm wrench.

3. Remove the fuel line from the fuel tank nipple: 3a. Squeeze the tabs on the fuel line clamp with a

pair of pliers while sliding the clamp down the fuel line away from the nipple.

1.10.

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

See Figure 1.9.

See Figure

Front fuel tank shroud

Remove these

screws

Figure 1.9

Fuel filter

3b. Gently work the fuel line off of the nipple.

Residual fuel in the fuel tank will

! WARN IN G! WARN IN G

mended to help prevent gasoline from splashing into your eyes.

4. Remove the fuel tank nipple using a 17 mm wrench.

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

NOTE: Apply a small amount of releasable thread locking compound such as Loctite® 242 (blue ) an d tigh ten

come out when the fuel line is removed. Safety goggles are recom-

the filter by hand and then an additional 3/4 to 1 full turn to compress the gasket.

Fuel line clamp

Figure 1.10

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Introduction

Valve lash

V alve 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 checked and adjusted using the following steps:

Muffle

Spark plug socket

Valve cover

Figure 1.11

Breather

hose

spring clamp

1. If the engine has been run, allow it to cool thoroughly. Position the equipment for easy access to the cylin der 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. Disconnect the breather hose from the valve cover. See Figure 1.12.

5. Remove the five bolts that secure the valve cover using a 10mm wrench. Remove the valve cover from the engine.

NOTE: If care is taken not to damage the valve cover gas-

ket, it can be re-used.

See Figure 1.11.

Figure 1.12

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6. Slowly pull the starter rope until air can be heard coming out of the spark plug hole.

7. Confirm that the piston is at Top-Dead-Center on the compression stroke.

• The compression stroke can be distinguished

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.

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

9. Intake valve lash (carburetor side) should be 0.004”-

0.006” (0.10 - 0.15mm).

See Figure 1.13.

See Figure 1.14.

Probe to confirm piston

is at top of travel

Valves closed

(push rods slack)

Push rods relaxed

Figure 1.13

.006” feeler

gauge

10. Exhaust valve lash (muffler side) should be 0.006-

0.008” (0.15 - 0.20mm).

11. Use a 10mm wrench to loosen the jam nut, and a 14mm wrench to adjust the rocker arm fulcrum nut. See Figure 1.15.

• 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.

• 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.

12. 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.

See Figure 1.15.

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Figure 1.14

.008” feeler

gauge

Figure 1.15

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Introduction

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

14. Rotate the engine through several compression cycles:

• Observe the movement of the valve gear.

• 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.

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

16. Install the valve cover, tightening the valve cover screws to a torque of 62 - 80 in-lbs (7-9 Nm). IMPORTANT: Over tightening the valve cover will cause it to leak.

17. Install the spark plug.

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.

NOTE: Mice and other critters tend to build nests inside the engine shrouds while the snow blower is stored

during the long off season.

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General torque specifications

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Frequently used specifications

Intake valve lash

Exhaust valve lash

Spark plug gap

Introduction

Minimum Maximum

in. mm in. mm

78 0.004 0.10 0.006 0.15 83 0.004 0.10 0.006 0.15

90 0.004 0.10 0.006 0.15

78 0.006 0.15 0.008 0.20 83 0.006 0.15 0.008 0.20

90 0.006 0.15 0.008 0.20

78 0.026 0.65 0.030 0.75 83 0.026 0.65 0.030 0.75

90 0.026 0.65 0.030 0.75

Module air gap

78 0.016 0.40 0.024 0.60 83 0.016 0.40 0.024 0.60

90 0.016 0.40 0.024 0.60

Displacement

78 16.9 cid (277 cc) 83 21.8 cid (357 cc)

90 25.6 cid (420 cc)

Governed engine RPM

78 3500 + 100 83 3500 + 100

90 3500 + 100

Oil capacity

78 37 oz 1.1 L 83 37 oz 1.1 L

90 37 oz 1.1 L

Fuel tank capacity

78 1.3 gal 5.0 L 83 1.3 gal 5.0 L

90 1.3 gal 5.0 L

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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! CAUTION

NOTE: The steps and the order of the steps that follow are a suggested approach to troubleshooting 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. Hard to pull rope, steady pressure B. Rope jerks back C. Rope will not pull at all

• Crankshaft turns, no start

• Starts, runs poorly

A. Starts, then dies B. Runs with low power output C. Makes 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

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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.

3. Broken starter rope. 3a. Usually means the engine was hard to start. 3b. Makes it impossible to confirm any running or hard starting symptoms by direct observation. 3c. Some inference can be made from checking other factors of the general condition of the equipment.

Identify factors that could cause the problem

This is the second step in the troubleshooting process.

1. Crankshaft will not turn.

A. Hard to pull rope, steady pressure. This usually indicates a mechanical bind of some sort. The likely

suspects are: I. A slightly bent crankshaft. In some cases the drag may increase and decrease as the crankshaft

rotates. This produces a pulsing feeling that is different than a jerk back. II. A parasitic load from a drive belt that is not releasing or an implement that is jammed. III. An internal drag from a scored or seized piston.

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BASIC TROUBLESHOOTING

D. Rope jerks back. This usually indicates that the piston is stopping before top dead center on the com-

pression stroke and is being driven back down by compression or combustion. The likely suspects are: I. Compression that is unusually high.

a. valve lash. b. a partial hydraulic lock.

III. Ignition timing is advanced.

a. Improper air gap. b. Sheared or missing flywheel key. c. The wrong flywheel or module is installed on the engine.

IV. Insufficient inertia to over-come normal compression .

a. Loose implement. b. A light flywheel used on a heavy flywheel application.

C. Rope will not pull at all. This is usually either a quick fix or a catastrophic failure. The likely suspects

are: I. A broken starter recoil (easy fix). II. Complete hydraulic lock (easy fix). III. External binding/jammed implement (easy fix). IV. Bent crankshaft (unrepairable) V. Internal binding, crankshaft, connecting rod or piston (unrepairable)

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 start 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 fr esh gasoline; in sufficient quantity, atomized (tiny droplets) and 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 go od one. IV. Check compression or leak down. V. Check valve lash.

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VI. Check valve timing/actuation. VII. Check exhaust.

3. Starts, runs poorly 3a. Starts, then dies

I. Run the engine with a spark tester in-line between the sp ark plug wire and the sp ark plug or use an

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 incr ease and decrease a s 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 accompa nied 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.

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BASIC TROUBLESHOOTING

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 performance.

• The intake valve not fully opening. A possible cause of this is loose valve lash.

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

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78/83/90 Series Horizontal Shaft Engines

• 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 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. Mixtu re not b urnin g 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.

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• 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 duri ng normal operations.

5. Engine RPMs surge (hunting) A. Over-governed condition- Return spring replaced with wron g 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

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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 gathered fro m the tro ubl eshooting th at was per forme 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: confirmin g 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.

• Make sure the customer understands th e repair , preventing “superstitious” come-backs.

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78/83/90 Series Horizontal 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 and the safety key if fully inserted.

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. 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.

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

See Figure 2.1.

3. Connect tester to compressed air.

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.

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Leak-down tester adapter

Figure 2.1

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