Toro 51921, 51920, 51926, 51927 Service Manual

AC-1 ENGINE SERVICE MANUAL

Table of Contents – Page 1 of 2

ABOUT THIS MANUAL

GENERAL INFORMATION
ENGINE SPECIFICAT IONS
FUEL AND LUBRICATION
IGNITION
TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS (CONT)
SAFETY WARNINGS AND NOTES
PRODUCT IDENTIFICATION NUMBERS
OIL AND FUEL RECOMMENDATIONS
STARTING/STOPPING INSTRUCTIONS
SERVICE/MAINTENANCE INSTRUCTIONS
STORAGE INSTRUCTIONS

TROUBLESHOOTING
ENGINE FAILS TO START
ENGINE STARVES ON ACCELERATION
ENGINE IS HARD TO START
ENGINE STALLS
ENGINE FIRES INTERMITTENTLY
ENGINE DOES NOT PRODUCE MAXIMUM POWER
CARBURETOR FLOODS
ENGINE STOPS AFTER RUNNING BRIEFLY
ENGINE WILL NOT IDLE
ENGINE BACKFIRES OR MISFIRES
ENGINE WILL NOT ACCELERATE
ENGINE LACKS POWER OR STOPS DURING OPERATION
ENGINE VIBRATES EXCESSIVELY
ENGINE USES EXCESSIVE AMOUNT OF OIL
STARTER ROPE IS DIFFICULT TO PULL OR ENGINE LOCKS

DISASSEMBLY
TYPICAL DISASSEMBLY SEQUENCE
REMOVE MAJOR COMPONENTS
DISASSEMBLE ENG IN E

INSPECTION AND REPAIR
CARBURETOR DISA SSEMBLY AND REASSEMBLY
STARTER DISASSEMBLY AND REASSEMBLY
BREATHER DISASSEMBLY AND REASSEMBLY
SPARK ARRESTER SCR EEN
PISTON/CONNECTING ROD DISASSEMBLY & ASSEMBLY
PISTON/CONNECTING ROD DISASSEMBLY & ASSEMBLY
CYLINDER HEAD INSPECTION & REPAIR

AC-1 ENGINE SERVICE MANUAL

Table of Contents – Page 2 of 2

INSPECTION AND REPAIR - Continued
CRANKCASE INSPECTION & REPAIR
MAJOR COMPONENTS INSPECTION & REPAIR

REASSEMBLY
TYPICAL ASSEMBL Y SEQU E NCE
ENGINE REASSEMBLY
INSTALL AIR FILTER BASE, AIR FILTER AND AIR FILTER COVER
ASSEMBLE HANDLE
ASSEMBLE COV ERS

ABOUT THIS MANUAL

This Service Manual was written expressly for the Toro AC-1 Four Stroke Engine. The Toro Company has made
every effort to make the information in this manual complete and correct. We are hopeful you' find this manual a

If

valuable addition to your service shop.

please contact us at the following address:

you have any questions or comments regarding the information inside,

The Toro Company

Consumer Service Training Department.

81

11

Lyndale Avenue South

!

Bloomington, MN

55420

The Toro Company reserves the right to change product specifications or this manual without notice.

Copyright@

1996

The Toro Company

All

Rights Reserved

General Information

.........................

B

Troubleshooting

Disassembly

Inspection and Repair ......................

Reassembly

.........................

..............................

...........................

.#

..

.,

..

.,

..

4

5

Table

Of

Contents

Engine Specifications
Fuel and Lubrication

ignition
Torque Specifications
Safety Warnings And Notes

Product Identification Numbers

Oil And Fuel Recommendations

Starting/stopping Instructions

Service/maintenance Instructions

......................................

Recommended Oil Type
Checking the Oil
Changing the Oil
Recommended Fuel Type

Definition of Blended Fuels
Use of Blended Fuels

Use of Fuel Additives

To Start the Engine
To Stop the Engine

Air Filter

..................................

...............................

...............................

...............................

..............................

.............................

............................

............................

...........................

..........................

.........................

..........................

.........................

.........................

.

...........................

...........................

...........................

........................

1-3
1-4
1-4

1-4
1-6
1-7
1-7

1-7

1-8
1-9
1-9
1-9
1-9

1-9

1-10
1-10

1-11
1-11

1-11
Spark Plug
Carburetor Adjustment
Definition of Optimum Setting for Idle Speed Mixture and

High Speed Mixture Adjustments
Rocker Arm to Valve Clearance Adjustment

Spark Arrester Screen

Storage instructions

To Reactivate Unit for Service

Special Tools

...................................

................................

..........................

.....................

...............

..........................

...............................

.......................

1-12
1-12

1-15
1-15
1-16

1-17
1-17

1-18

1

-2

j

Item

B

Engine Type

___

Displacement

~~

~~

~

~~

Air-cooled, 4-Cycle

Stroke

~__~

Average Compression
Piston Rings Side Clearance

~~-~___

Top Piston Ring Width
Top Piston Ring End Gap
Middle Piston Ring Width

_____~.

Middle Piston Ring End Gap

-

~ ~~

Oil Piston Ring Width
Oil Piston Ring End Gap

~____

Rocker Arm to Valve Clearance

~~~

~-

-~

~__

-

__~

__~_____--

_-

~~

-

_-

~~~

~

~-

~~

-~

~

__

~~

~~

1

-3

11

Approx Fuel Tank Capacity

TORQUE SPECIFICATIONS

18

oz

(530

ml)

tem

Carburetor/Air Filter Base Plate Mounting Screws

~~~~~

Carburetor Mount Insulator Screws

~~

Clutch Housing/Drum Assembly Screws

_.

~ . ~

_~~_~~~-_____-~_--

-

--~__

~

~ ~~ ~

-

Clutch Rotor
Cylinder Head Hex Nuts
Cylinder Screws
Spark Plug

~

-.

~

-

-

.

-.

..

_.._..____

. .___

Rear Engine Cover Screw
Front Engine Cover Screws

~

.

.

.

~~

~~

__

~~

-

-

1-4

SAFETY WARNINGS AND NOTES

WARNING: Hot Surfaces!

The purpose of safety symbols is to attract your atten­tion to possible dangers. The safety symbols and the
explanations with them, deserve your careful attention
and understanding. The safety warnings do not by
themselves eliminate any danger. The instructions or
warnings they give are not substitutes for proper acci­dent prevention measures. Some general warnings
follow.

WARNING: Spring Under Tension!

The rope starter on these engines contains a flat wire
spring that is under tension. Wear eye and hand protec­tion when replacing worn or broken spring, in case it
should uncoil as it is handled. Allow spring tension to
be completely relieved and make sure pulley disen-

.

gages from spring before removing the pulley retain-

ers, pulley, and starter spring from housing.

,

WARNING: Electrical Shock!

Never touch electrical wires or components while the
engine is running. They can be sources of electrical
shock.

The muffler, cylinder, crankcase, trimmer cutting head,
and other engine surfaces get extremely hot from op­eration. These surfaces remain hot for a short period
of time after the engine is stopped. To prevent severe
burns, allow the engine to cool completely before serv­icing.

I

WARNING: Explosive Fuel!

Gasoline may be present in the fuel tank, carburetor,
fuel lines, or crankcase. Gasoline is extremely flamma­ble and its vapors can explode

if

ignited. Keep sparks,
flames, and other sources of ignition away from the en­gine.

Do

not smoke while servicing the engine. Never

use gasoline as a cleaning agent.

in

not

well-

fill

the fuel

~

Store gasoline only in approved containers,
ventilated, unoccupied buildings, away from sparks,
flames, or other sources of ignition.

Do

tank while the engine is hot or running, since spilled

fuel could ignite

sparks from ignition.
spilled fuel.

if

it comes in contact with hot parts

Do

not start the engine near

Do

not smoke while handling gasoline or

or

filling the fuel tank.

i

.

WARNING: Cracked Or Broken Flywheel Fins
Can Become Projectiles!

Be careful not to crack or break any flywheel cooling

fins. They could fly

off

during operation.

If

cooling fin:

are cracked or broken, replace the flywheel.

1

-6

PRODUCT IDENTIFICATION

NUMBERS

When ordering parts, or in any communication involv­ing an engine or product, always give the:

Model Number, and
Serial Number

NOTE:

BEFORE Attempting TO START
THIS UNIT. Using old oil or fuel can cause engine
damage. This type of damage will void the engine
warranty

READ

THESE INSTRUCTIONS

CAREFULLY

OR

OPERATE

These numbers are located on a decal (or decals) af­fixed to the unit (Figure 1-1). The identification de-

will be located on the metal boom. The actual

location will vary depending on the type of product.

Figure 1-1. Product Identification Decal

1.0762.005

.

OIL AND FUEL

RECOMMENDATIONS

Recommended Oil Type

Toro 4-cycle oil is recommended for use in this engine

(Figure 1-2).

high

quality SAE

troleum Institute) service class SG,
Using the proper type and weight of oil in the oil pan is

extremely important. Check the oil before each use
and change the oil regularly. Failure to use the correct
oil, or using dirty oil, can cause premature engine
wear and failure.

If

another brand 4-cycle oil is used, use a

30

weight oil of API (American Pe-

SF,

SH.

TORO,

FOUR-CYCLE

ENGINE

OIL

,.

WARNING: Explosive Fuel!

Gasoline
can explode if ignited. Store gasoline only in ap-

proved containers, in well-ventilated, unoccupied
buildings, away from sparks or flames. Do not fill
the fuel tank while the engine is hot or running,

since spilled fuel could ignite if
with hot parts or sparks from Ignition. Do not start
the engine near spilled fuel. Do not smoke while

handling gasoline. Never use gasoline as a clean­ing agent.

Is

extremely flammable and its vapors

it

comes

in

contact

I--------

Figure 1-2. Recommended Oil Type.

3.6051.002

1

-7

Checking the

Oil

The importance of checking and maintaining the

proper oil level in the oil pan cannot be overempha-

sized. Check the oil

1.

Make sure the engine is stopped, level and is cool

so

the oil has had time to. drain into the oil pan

(Figure

1-3

BEFORE EACH USE

as follows:

for straight shaft units or Figure

1-4

for curved shaft units).

1-3.

Figure

Figure

2.

To keep dirt, grass clippings, etc. out of the engine,
clean the area around the oil

Level Engine - Straight Shaft Unit.

1-4.

Level Engine - Curved Shaft Unit.

fill

plug before remov-

3.6051.020

3.6051.004

ing it.

3.

Remove the oil
into the crankcase. Thread the oil

fill

plug; wipe the oil

off.

Reinsert it

fill

plug into the

oil pan.

4.

Remove the oil
(Figure

1-5).

fill

plug and check the oil level

Figure

1-5.

Removing Oil Fill Plug.

2.6051.005

The oil level should be up to the top of the dipstick

(Figure

1-5).

Full

(3.40z/lOOml)

Add Oil

L

Figure

5.

1-6.

Oil Level

If

the oil level is low, add the oil to the top

the dipstick (see Figure

3.6051.006

1-6).

Always check the

of

level with the dipstick before adding more oil.

1

-8

Changing the Oil

For a new engine, change the oil after the

hours

every

of operation. Thereafter, change the oil after

25

hours

or before storing the unit for an ex-

tended period of time.

first

10

NOTE:

To prevent extensive engine wear or damage,

always maintain the proper oil level in the crankcase.

Never operate the engine with the oil level below the
bottom of the dipstick

Recommended Fuel Type

Change the oil while the engine is still warm. The oil

will flow freely and carry away more impurities.

Change the oil as follows:

1.

Remove the oil

2. Pour the oil into a container by

in a vertical position (Figure

fill

plug.

tipping the trimmer

tipping

7).

Be sure to allow

1-7

ample time for complete drainage. Dispose of oil
properly.

Use clean, fresh, regular grade unleaded gasoline less

than

60

days old.

NOTE:

(water). As little as

Alcohol blended fuel absorbs moisture

1

%

moisture in the fuel can cause

fuel to separate and form acids when stored.

If

these types of fuel must be used, use fresh fuel (less

than

60

days old).

Definition

of

Blended Fuels

Today's fuels are often a blend of gasoline and one Or
more oxygenates such as ethanol, methanol or MTBE

(ether).

Use of Blended Fuels

If

you choose to use a blended fuel or its use is un-

avoidable, the following precautions are recom-

mended.

1-7.

Figure

Pouring Oil.

3. Fill the oil pan, with 3.4 oz

3.6051.007

(100

ml) of new oil of the

proper type, to the top of the dipstick.

4.

Reinstall the oil

NOTE:

Make sure the O-ring is in place on the oil

fill

plug and tighten securely.

plug when checking and changing the oil.

fill

1.

Always use fresh fuel.

2. Use the special additive Toro Gas Conditioner/
Stabilizer, STA-BIL

(R)

or an equivalent.

3. Drain the fuel tank and run the engine dry before
storing the unit.

Use of Fuel Additives

The use of fuel additives, such as Toro Gas Condi­tioner/Stabilizer, STA-BIL Gas Stabilizer or an equiva-
lent, will inhibit corrosion and minimize the formation
of gum deposit. Add

0.8

oz (23 ml) per gallon of fuel
per instructions on the container. NEVER add fuel ad-
ditives directly to the unit's fuel tank. Using a fuel addi-

60

tive can keep fuel fresh for up to

days.

1-9

STARTING/STOPPING

INSTRUCTIONS

To

Start

the Engine

1.

Set the unit on the ground, check the oil level in the
oil pan, and put the ignition switch in the “RUN”
position (Figure 1-8).

---Run position
Partial Choke

choke

(I)

Figure 1-8. Ignition Switch and Throttle Trigger.

2.

FULLY PRESS AND RELEASE the primer bulb 5 to

7

times (Figure 1-9).

NOTE:

For a warm engine, go directly to step

3.6051.008

5

(place the choke lever directly in the “PARTIAL” choke

position).

Figure
Positions.

1-9.

Primer Bulb, Choke Lever and Choke

3.6051.009

4.

With the unit on the ground, pull the starter rope
quickly until the engine sounds like it wants to run

5

(no more than

pulls) (Fig. 1-10).

,

3.

Place the choke lever

tion (Figure 1-9).

1-10

in

the FULL “CHOKE” posi-

Figure 1-1

0.

Pulling the Starter Rope.

3.6051.010

5.

Place the choke lever in the “PARTIAL” choke posi­tion (see Figure 1-9 on page 1.4). Pull the starter
rope quickly until the engine starts (no more than

5

pulls).

6.

If

the engine does not start, repeat steps 2 to 8.

7.

Run the engine for

lever fully squeezed (see Figure 1

30

seconds, with the throttle

-6),

to warm up.
Place the choke lever in the “RUN” position
(Figure 1-9).

2.

Wash the air filter in detergent and water
(Figure 1-11). Rinse the air filter thoroughly in
clean water and allow

it

to dry.

NOTE:

In colder weather, run the engine for 2 to

3

minutes to warm up.

To

Stop the Engine

Place the ignition switch in the “STOP position (see
Figure 1-8).

SERVICE / MAINTENANCE

INSTRUCTIONS

Air Filter

NOTE:

CLEAN AND

EVERY 10 HOURS

one of the most important areas to maintain.

maintained as follows, poor engine performance and

severe engine damage can result.

1. Remove the three
filter cover assembly. Remove the air filter cover
and air filter. Refer to

RE-OIL

OF

(3)

THE

AIR

FILTER

OPERATION. The air filter is

screws on the carburetor/air

Part

3

-

Engine

Disassembly

\

If

it is not

L

Figure 1-1 1. Washing Air Filter Element.

3.

Apply clean SAE

Figure 1-1

2.

Oiling Air Filter Element.

30

oil to the air filter (Figure 1-12).

3.6051.012

3.6051.011’

I

I

4. Squeeze the air filter to ensure that the oil is spread
throughout the entire filter (Figure 1-13).

1-11

L

Figure 1-13. Squeezing Excess Oil from Air Filter
Element.

5.

Spark Plug

3.6051.013

Reinstall the air filter in the carburetor/air filter
base. Refer to

Part

5

-

Engine Reassembly

NOTE:

Do not clean the spark plug in a machine

~

which uses abrasive grit. Some grit could remain on

the spark plug and enter the engine causing extensive

damage.

4. Check the spark plug gap using a wire feeler gauge.
Set the gap to

5.

Reinstall the spark plug and torque to

(1 1.3-1 2.3

0.025 in

N-m).

(0.635

mm)(Figure 1-14).

100-110 in-lb

Use a Champion RDZ19H spark plug. Every 50

hours

of operation, remove the spark plug, check its condi­tion, and reset the gap or replace with a new plug as

necessary. Allow the engine to cool before removing

the spark plug.

WARNING: Electrical Shock!

Never touch electrical wires or components while the
engine is running. They can be sources of electrical

shock.

1. Before removing the spark plug, clean the area
around the base of the spark plug to keep dirt and
debris out of the engine.

2.

Disconnect the spark plug wire and remove the
spark plug from engine.

3.

Inspect the spark plug for carbon buildup and clean

if

necessary. Replace the plug

if

reuse is questionable.

if

it is badly burnt or

Figure 1-14. Spark Plug Gap.

Carburetor Adjustment

3.6051.014

-

These engines are equipped with a diaphragm-type
carburetor. The carburetor has been carefully cali-

~

brated at the factory. In most cases, no further adjust­ment will be required.

The condition of the air filter is very important to the

(

eration of the trimmer. A dirty air filter will restrict the
air flow to the carburetor. This in turn upsets the fuel­air mixture in the carburetor. The resulting symptoms
are often mistaken for an out-of-adjustment carburetor
Therefore, check the condition of the air filter before
adjusting the carburetor. Refer to “Air Filter“ Serv­ice/Maintenance Instructions.

I-

1-12

-

If

the following conditions are experienced, it may be

necessary to adjust the carburetor.

The engine will not idle
The engine hesitates or stalls on acceleration.
The

loss

of engine power, which is not corrected
by cleaning the air filter, muffler, spark arrester
screen or adjusting the rocker arm to valve
clearance

The engine operates in an erratic or fuel-rich
condition

NOTE:

Follow these carburetor adjustment proce­dures carefully. An incorrectly adjusted carburetor can
cause severe engine damage.

407000001-Use the following carburetor adjustment
instructions:

1.

Initial Idle Speed Setting:

Turn the idle speed

screw until it stops.

2.

Initial High Speed Mixture and Idle
ture Settings:

and idle mixture needles

Turn both the high speed mixture

in (clockwise)

Speed

until they

Mix-

are lightly seated.

3.

Turn the needles

following number

out

of

turns:

the

High Speed Mixture Needle: 1 turn

Idle Speed Mixture Needle:

1

turn

Make sure the unit is fully assembled before

making carburetor adjustments.

For trimmers

and

brushcutters, make sure

the boom, cutting head, and line guard are installed

and the cutting line is extended to its full cutting length.

The carburetor has three basic adjustments: the idle

speed adjustment, the idle speed mixture adjustment,
and the high speed mixture adjustment (Figure 1-15).

Mixture Needle

NOTE:

Turn the high speed mixture and idle mixture

needles finger-tight. Do not force the needles with a
screwdriver as this can damage the tips of the needles
and the seats in the carburetor body.

4. Start the engine and let it run for

3

to 5 minutes

with the throttle lever fully squeezed.

5.

Release the throttle trigger and let the engine idle.

Turn the idle speed screw

until the speed decreases and the bump

wise)

out (counterclock-

head stops rotating.

6.

Final Idle Speed and Mixture Adjustments:

Adjust the idle speed screw and idle speed mix­ture needle for the smoothest engine idle using

Do

the following procedure.

not squeeze throttle
trigger when adjusting the idle speed screw and
idle speed mixture needle.

a. Set the idle speed mixture needle

at the optimum setting
(Figure 1-16). See “Definition of Optimum
Setting” on page

1-1

5.

Figure

1-1

5.

Carburetor Adjustments.

3.6051.015

1-13

b

b. Squeeze the throttle trigger.

falters or hesitates as
idle speed mixture needle

wise) 1/16 turn at a time

celerates rapidly.

it

If

the engine

accelerates, turn the

out (counterclock-

until the engine ac-

3.

Turn the needles
following number of turns:

High Speed Mixture Needle: 1 1/8 turns

out (counterclockwise)

the

c.

If

the idle speed has changed significantly be­cause of steps a. and b. above, readjust the
idle speed screw.

7.

Final High Speed Mixture Setting:

Adjust the high speed mixture needle as follows:

a. Squeeze the throttle trigger and

run the unit at high speed for

b. While squeezing the throttle trigger fully, set

the high speed mixture needle at the optimum
setting. See “Definition of Optimum Setting”
on page 1-1 5.

NOTE:

must be the last adjustment made
the idle speed mixture needle is adjusted, the high
speed mixture needle must be readjusted.

8.

For Units with Engine Serial Number 407000001

and Greater-Use

ment instructions:

The high speed mixture needle adjustment

Make sure the air filter cover is reinstalled securely
before placing the unit back into service.

the following carburetor adjust-

3

to 5 minutes.

on

the carburetor.

Idle Speed Mixture Needle1 1/8 turns

NOTE:

mixture needles using finger pressure. Forcing the mix­ture needles will damage the tips of the needles and

the seats in the carburetor body.

4.

5.

6.

If

NOTE:

justment is made, no more high speed mixture needle

adjustments to the carburetor are necessary.

Seat the high speed mixture and idle speed

Start the engine and let it run for 3 to 5 minutes
with the throttle lever fully squeezed.

Release the throttle trigger and let the engine idle.

If

the engine stops, turn the idle speed screw

(clockwise) 1/8 turn

the engine idles.

Final High Speed Mixture Needle Adjustment:

a. While squeezing the throttle trigger fully, set

the high speed mixture needle at the optimum
setting. See “Definition of Optimum Setting”.

After the final high speed mixture needle ad-

at a time (as required) until

in

~

1.

Initial Idle Speed Setting:

screw (Figure 1-15)
it

does not contact

Then turn the screw

gins

to move the throttle lever; then continue turn-

ing

2

full turns.

2.

Initial High Speed Mixture and idle Speed
Mixture Settings:

ture and idle speed mixture needles

wise)

until they are

out (counterclockwise)

the carburetor throttle lever.

in (clockwise)

Turn both the high speed mix-

lightly seated.

Back the idle speed

1-14

until it

just be-

in (clock-

until

7.

Final Idle

Adjustments:

idle speed mixture needle for the smoothest en­gine idle using the following procedure. Do not
squeeze the throttle trigger when adjusting the idle
speed screw and idle speed mixture needle.

a. Set the idle speed mixture needle at the

b. Turn the idle speed mixture needle

Speed

optimum setting (Figure 1-16). See “Definition’
of Optimum Setting”.

(counterclockwise) 1/8 turn

of optimum.The engine should idle and accel­erate smoothly.

and Idle Speed Mixture

Adjust the idle speed screw and

out

to the rich side

’

~

~

~

8.

Final Idle Speed Adjustment:

speed by turning the idle speed screw

wise)

or

out (counterclockwise)

head does not rotate.

Do

Adjust the idle

in (clock-

until the cutting

not squeeze the throttle

trigger when adjusting the idle speed screw.

9.

Make sure the air filter cover is reinstalled securely

before placing the unit back into service.

Definition of Optimum Setting for Idle Speed
Mixture and High Speed Mixture Adjustments

Always set the idle speed mixture needle and high
speed mixture needle at the optimum setting. To find

the optimum setting, use the following procedure.

1. Turn the adjusting needle

out (counterclockwise)

from the preliminary setting until the engine speed

decreases (rich). Note the position of the needle.

2.

Turn the adjusting needle

in (clockwise).

The en­gine speed may increase as the needle is turned
in (lean). Note the position of the needle.

Rocker Arm to Valve Clearance Adjustment

50

hours

Every

of operation, remove the rocker

arm

cover and check the rocker arm to valve clearance.

1.

Remove the four

(4)

screws from the engine cover.
Remove the engine cover. Remove the rocker arm
cover. Refer to

2.

Position the crankshaft

Part

3

-

Engine Disassembly.

so

that the piston is at the
top of the compression stroke (both rocker arms
are free and loose).

3.

Measure the clearance between the valve stems
and rocker arms, using a

1-17).

flat

feeler gauge (Figure

3.

Set the adjusting needle

midway

and the lean settings (Figure 1-16).

Adjust to

Midpoint

Figure 1-16. Optimum Setting.

3.6051.016

between the rich

Lean

I

Figure 1-17. Measuring the Rocker Arm to Valve

Clearance.

3.6051.017

The recommended rocker arm to valve clearance for
both the intake and exhaust is

(.076

mm-,152 mm).

.003-.006

in

4.

If

the clearance is not within specification, adjust as

follows:

Spark Arrester Screen

b

To

the adjusting nut counterclockwise.

To

the adjusting nut

5.

a. Turn the adjusting nut (Figure 1-18), using a

5/16 in (8 mm) wrench or nut driver.

increase the rocker arm to valve clearance,

decrease the rocker arm to valve clearance,

clockwise.

b. Recheck the clearance with a flatfeeler gauge

and readjust as necessary (see Figure 1-1

Reinstall the rocker arm cover, using a new gasket.
Torque the rocker arm cover screw to

(2.2-3.4 N.m).

20-30 in-lb

turn

turn

7).

This unit is equipped with a spark arrester screen.

50

hours

Every

screen for debris and/or deposits.

WARNING: Hot Surfaces!

Make sure the muffler is cool before checking the
spark arrester screen to prevent injury.

1. Remove the spark arrester cover screw and cover
(Figure 1-1

of operation, check the spark arrester

9).

Figure 1-18. Adjusting Nuts.

6. Install the breather hose to the air filter base.

7.

Reinstall the engine cover and screws. Refer to
Part

5

-

Engine Reassembly.

Torque the top screws to
Torque the front screw to
Torque the rear screw with washer to

4.0

Nom).

2.6051.018

15-20 in-lb (1.7-2.2 Nom).

20-25 in-lb (2.2-2.8 Nom).

30-35 in-lb (3.5-

1-16

Figure 1-1

2.

3.

4.

9.

Spark Arrester Screen.

Push the spark arrester screen out of the cover.

Inspect the spark arrester screen.

If

the screen is clean, reinstall the screen,
cover and screw.
replace it.

Torque the screw to

If

the screen is plugged,

15-20 in-lb (1.7-2.2 N-m).

3.6051.019

STORAGE

WARNING: Explosive Fuel!

Gasoline is extremely flammable and its vapors can
explode if ignited. Store gasoline only in approved con­tainers, in well-ventilated, unoccupied buildings, away
from sparks or flames. Do not
the engine is hot or running, since spilled fuel could

if

ignite
from ignition. Do not start the engine near spilled fuel.
Do not smoke while handling gasoline. Never use
gasoline as a cleaning agent.

1.

2.

3.

it comes in contact with hot parts or sparks

Drain all fuel from the fuel tank.

that has been stored for more than

Start the engine and run it until it stalls. This
ensures that all fuel has been drained from the
carburetor.

Drain the oil from the crankcase and add fresh oil

(3.4

oz

to lubricate the engine.

INSTRUCTIONS

fill

the fuel tank while

Do

not use fuel

60

/100

ml). Pull the starter rope a few times

days.

Figure

To

1.

2.

3.

1-21.

Storing a Curved Shaft Unit.

Reactivate Unit for Service

Remove the spark plug and drain the oil from the
cylinder by slowly pulling the starter rope.

Reinstall the spark plug.

Refuel the unit with fresh gasoline. Start engine in

accordance with the

Starting Instructions.

3.6051.021

4.

Allow the engine to cool. Remove the spark
plug and put several drops of any

30

quality SAE

Petroleum Institute) service class SG,

into the cylinder. Pull the starter rope slowly to dis-

tribute the oil. Reinstall the spark plug.

5.

Clean the unit and inspect for any loose or
damaged parts. Repair or replace damaged parts
and tighten loose screws, nuts, or bolts.

6.

Store the unit in a 'dry, well ventilated area. Place

unit

the
for straight shaft units or Figure
shaft units).

flat on the floor or on a table (Figure

weight oil of API (American

high

1-21

SF,

for curved

SH

1-20

Figure

1-20.

Storing a Straight Shaft Unit.

3.6051.020

~

Special

Tools

In addition to typical hand tools, the following special

tools are required to properly service this engine:

Clutch Rotor
Flywheel Holding

Tool,

P/N 180918 (Figure 1-22).

Tool,

P/N 180919 (Figure 1-23).

0-250 in-lb (0-28.1 N.m) Torque Wrench
(Commercially available).

Toro (R)

Screwdriver or Bit Set (Commercially

available).

Two-stroke, Magnetic Pick-up Tachometer

(Commercially available).

Figure 1-23. Flywheel Holding Tool, P/N 18091 9.

3.6051

.023

Figure 1-22. Clutch Rotor

1-1

8

Tool,

P/N 180918.

3.6051.022

General Information

.

...........................

.

Troubleshooting

Disassembly

Inspection and Repair

Reassembly

......

......

. .

.

...........................

...........................

............................

2.

5

2-1

Table

Of

Contents

Engine Fails
Engine Starves On Acceleration
Engine
Engine Stalls
Engine Fires Intermittently
Engine Does Not Produce Maximum Power
Carburetor
Engine Stops After Running Briefly
Engine Will Not Idle
Engine Backfires

Engine Will Not Accelerate
Engine Lacks Power Or Stops During Operation

Engine Vibrates Excessively
Engine Uses Excessive Amount Of Oil

Starter Rope

Is

Hard

To

Start

...............................

.........................

To

Start

..............................

....................................

.............................

Floods

.................................

........................

................................

Or

Misfires

...........................

............................

...........................

......................

Is

Difficult

To

Pull Or Engine Locks

...................

2-8

.................

.................

2-8

2-9
2-9
2-9

2-3
2-4
2-4

2.5
2-5
2-6
2-6
2-7
2-7
2-7

2-2

c’

When difficulties occur, be sure to check for simple
causes which, at first, may seem too obvious to be
considered.

A

starting problem, for example, could be

caused by an empty fuel tank.
The following table lists some common causes of

operating troubles and the possible causes and

remedies.

I

-

Engine Fails

__

~-

;Possible

L-

Ignition switch in STOP

-~

~_~~~___

~-

~~ ~

Cause

To

.-

~~

_____

Start

~-

_

~.

(0)

position

_

.

~~ ~

-

-

___

~~

~-__

Out of fuel or water in fuel

~~

-___

Dirty or plugged air filter
Loose spark plug lead wire

__~____~

-

.-

~

Fouled, improperly gapped or broken spark plug

__~._

Plugged fuel tank cap vent
Plugged or waterlogged fuel filter

-

~_____~

Improperly adjusted carburetor

____-

Plugged muffler

-

Faulty primer or primer/fuel lines improperly installed

~.

-

-.

Plugged fuel line
Faulty carburetor diaphragm

____

Plugged spark arrester screen
Faulty fuel pump diaphragm

-

~.

_____

~~

.__

~-

-

_____

__

-

Plugged carburetor/fuel pump passages

&

Incorrect air gap between flywheel

ignition module

__

Faulty ignition module

Low

compression

_________~.~

.~

Rocker arm to valve clearance is out of adjustment

_~_____~_

___.

~~ ~~

~.__________

-

~-

~ ~~

-

i

~~ ~ ~

-~

~~~ ~~ ~

~

~-

__

-

__

~~

-_

Remedy

Place switch in

~

RUN

(I)

position

-~~

Drain tank and blow out fuel lines to remove water

Refuel tank with fresh fuel

-_

Clean or replace air filter

Reconnect lead wire

.~____

____

~

___~~

~-____

Clean or replace spark plug; set gap to 0.025 inch

(0.635

Clean fuel tank cap vent

Replace fuel filter

Adjust carburetor

mm)

__

~-

~-

~.-~____-~

~~

__

-~

~-

__

__~-

.-

~-

Clean or replace muffler
Correctly install primer/fuel lines or replace primer

~

____~.._~_.________

Blow out fuel line
Replace diaphragm

~~

Clean or replace spark arrester screen
Replace pump diaphragm

~~~ ~

Clean out passages

__

~.

~~~

-.

~~

.~

~~

~-

~

Set ignition module air gap to

0.008-0.01

-

Replace ignition module

_~_____

Replace piston rings or cylinder

_

2

in (0.201

.-

~~~~

-0.305

__

mm)

~-

--

Adjust rocker arm to valve clearance

___

~ ~~~

~

_

_~_

~_ _~

~-

~-

~ ~

__

-

~ ~~ ~

__

-~

8.

~~ ~

~-

~__

____

~-

~

I-

____

__

I

_~

~-

__

2-3

1

8

Engine

possible

.

Cause

Is

Hard

To

~___~~

Start

~~

Fouled, improperly gapped or broken spark plug

Plugged or waterlogged fuel filter

___.

-

Improperly adjusted carburetor
Clogged muffler

~~

Faulty primer or primer/fuel lines improperly installed

~~

Incorrect air gap between flywheel and ignition module

-

Faulty ignition module
Plugged spark arrester screen

~-

.~

~

Rocker arm to valve clearance is out of adjustment
Worn or improperly adjusted carburetor jet needle
Faulty carburetor diaphragm
Faulty fuel pump diaphragm

~~

-

~~

__

__

..

~

.~

-

~~

-

~

-

~.

_____~~~

_____

~

-~

~

________

Low compression

_

-~

~~~~ ~

.

~~~

___

~ ~~ - ~

Remedy

-

~~

~ ~ ~~ ~

Clean or replace spark plug;

~~

set gap to 0.025 inch

~~~

Replace fuel filter

Adjust carburetor

Clean or replace muffler

_-

-

_

~~____~-~

~ ~~ ~ ~~~

~

-~

~

(0.635

mm).

~

Correctly install primer/fuel lines or
replace primer

~-

Set ignition module air gap to

0.008-0.01 2 in (0.201
Replace ignition module

___~_~~

Clean or replace spark arrester screen

_____~

_____~

~-

~_

Adjust rocker arm to valve clearance

_

Adjust or replace needle

~

Replace carburetor diaphragm

_

-

Replace fuel pump diaphragm

..

~ ~ ~

~~

~~~~~

_

~~ ~

~_-

-0.305

~~

_

~~~ ~ ~

_~

mm)

~ ~

___________~~~

Replace piston rings or cylinder

~

.

_-

~~~

___~_~_____~_~

-.

.

~

-

-

~-

.~

~

.~

~

_

~~

I

~

-

,

___

~ ~

~

~

_____

2-4

Engine Stalls

Plugged fuel tank cap vent
Improperly adjusted carburetor
Plugged muffler
Plugged spark arrester screen
Plugged fuel line

-

Faulty ignition module

___-

-

__~

~-

~

-~

.~___

~

-_

Clean or replace spark plug; set gap to

0.025

inch

-

-.

~~

(0.635

Clean fuel tank cap vent
Adjust carburetor

mm)

~

_.

_.

~-

__

_.

Clean or replace muffler

~

~-

~~ ~~

Clean or replace spark arrester screen

Blow

out fuel line

Replace ignition module

____

~

~

~-

~-

~

--~

~-

~

-~

__

-___

~

~

--

-

__~

~-

Engine Fires Intermittently

Fouled, improperly gapped or broken spark plug

____-

incorrect air gap between flywheel and ignition module

improperly adjusted carburetor

~ ~

-~

Faulty ignition module

-

~

__---

Remedy

~ ~~

Clean or replace spark plug; set gap to

0.025

inch

--

~

(0.635

mm).

-~___

Set ignition module air gap to

0.008-0.01

~~

Adjust carburetor

Replace ignition module

~-

~ ~~~

2

in

______~

____

--

(0.201

-.

-

~ ~~ ~

-0.305

~-

__

mm))

-

2-5

,

Engine Does Not Produce Maximum Power

Plugged muffler
Plugged spark arrester screen

Plugged or waterlogged fuel filter

-.

..

~

~ ~ ~~~ ~

~~ ~~~~ ~ ~~~

Improperly adjusted carburetor

Air leak at carburetor base gasket

Intermittent spark
Low compression

Scored piston and/or cylinder

._

~ ~~ ~

~p

~ ~

..

-

.

.

Worn piston rings or low compression
Cam gear improperly timed

Valves leaking

~~~

~_~

~.

~~

~ _ ~

__

~

Carburetor

Floods

pp~_~

~~~ ~~~

ulty primer or improperly installed primer/fuel lines

_. . .

.

.. . ...

~

11

Damaged carburetor
Leaking fuel inlet needle

11

~.

2-6

~~~

~~~~ ~

I

Remedy

.

. .

~_

Engine

_~_____.

possible Cause

i

Stops

~__~~

~~~~

After Running Briefly

-~

~ ~~

Partially plugged fuel tank cap vent
Dirty or plugged air filter

Water in fuel

________

~~

Air leak at carburetor base gasket

Dirty carburetor fuel inlet needle or passage

~~

__

Faulty carburetor diaphragm

_______~~

-~

-~__

~

~~

~~___~~~__

Clean or replace air filter

~.

~~

__

Drain tank and blow out lines

~~~~

~~__

Tighten carburetor mounting fasteners or

replace carburetor base gaskets

-

-~

~~ ~

__~_

Replace fuel inlet needle or clean out carburetor

_-.___~.________

~~.~~_____~-

~___~~-~

Replace diaphragm

~

~~

~-

Losing compression

Engine

Possible g Cause

__~

Improperly adjusted carburetor

___~~________

Dirty or plugged air filter Clean or replace air filter
Faulty carburetor diaphragm Replace carburetor diaphragm
Faulty carburetor inlet seat gasket Replace carburetor inlet seat gasket

Will

~ ~

Not

Idle

~ ~~ ~~ ~~ ~~

~___

~______________~

Leaking crankshaft seal Replace crankshaft seal

Scored cylinder or low compression

____

i

~~1

-_

~ ~ ~

-

.-~.____._~

-$

.__~__

I

I

Replace piston rings or gaskets or

overhaul engine

___________-__

~~~ ~

~-

Remedy

~~ ~~~ ~~ ~~~ ~~

Adjust carburetor

~~

~~

________

__

~~

~~-.

-~

~ ~

-

.~

-

~__

~____-~

~-

~

~-

~

-

Overhaul engine

--

~-

~-

__

~

Engine Backfires Or Misfires

possible Cause

~

~

~-

~

Fouled, improperly gapped or broken spark plug

.

.___

Shorted ignition module leads

Rocker arm to valve clearance is out of adjustment

-

Weak valve spring

,__-

~~

-

~. _____.~~

~ ~

___~

~~

~

~-

~~

Check for loose or bare wires or loose
assembly and corrector replace ignition module

Adjust rocker arm to valve clearance

-_

-

-~

~___

-

Replace valve spring

~~~~ ~

2-7