MTD AC3 Series Shop Handbook

Brand: MTD

Model: AC3 Series

Type: Shop Handbook

Preliminary Shop Handbook

AC3 Edger

MTD Products Inc - Product Training and Education Department

FORM NUMBER - 769-02775

10/2006

NOTE: These materials are for use by trained technicians who are experienced in the service and repair of outdoor power

equipment of the kind described in this publication, and are not intended for use by untrained or inexperienced individuals.

These materials are intended to provide supplemental information to assist the trained technician. Untrained or inexperi-

enced individuals should seek the assistance of an experienced and trained professional. Read, understand, and follow all

instructions and use common sense when working on power equipment. This includes the contents of the product’s Oper-

ators 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 complete and accurate 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.

1. INTRODUCTION ........................................................................................................................1

2. PERIODIC MAINTENANCE........................................................................................................2

3. INITIAL TROUBLESHOOTING...................................................................................................5

4. TROUBLESHOOTING THE IGNITION SYSTEM .......................................................................7

5. TROUBLESHOOTING THE FUEL SYSTEM..............................................................................9

6. TROUBLESHOOTING/ REPAIRING THE CARBURETOR......................................................10

7. BLADE AND BELT...................................................................................................................14

8. STARTER..................................................................................................................................16

9. FUEL SYSTEM..........................................................................................................................17

10. IGNITION SYSTEM...................................................................................................................19

Table of Contents

1. INTRODUCTION

For the 2007 season, MTD introduced a compact

edger. This edger uses the new AC3 four cycle engine

that was introduced in the spring of 2006.

Disclaimer: This handbook was written using a proto-

type. The information contained in this handbook is

correct at the time of writing. Both the product and the

information 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 procedure.

CAUTION: is used to point-out potential danger

to the technician, operator, bystanders, or sur-

rounding property.

• Bullet points: indicate sub-steps or points.

Disclaimer: This Preliminary Shop Handbook 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 proce-

dures described in the text.

• If the person using this manual is uncomfortable

with any procedures they encounter, they should

seek the help of a qualified technician.

Figure 1.1

Fasteners:

• Most of the fasteners used on the blower are

sized in fractional inches. Some are metric.

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 the do not show signs of wear or

damage. This manual leaves that decision to

the judgement of the technician.

Assembly:

Torque specifications may be noted in the part of the

text that covers assembly, they may also 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.

The level of assembly instructions provided will be

determined by the complexity and of reassembly, and

by the potential for unsafe conditions to arise from mis-

takes made in assembly.

Some instructions may refer to other parts of the man-

ual for subsidiary procedures. This avoids repeating

the same procedure two or three times in the manual.

AC3 Edger

2. PERIODIC MAINTENANCE

Periodic maintenance consists of:

• Changing the oil.

• Cleaning the spark arrester

• Checking and adjusting the valves.

• Changing the spark plug.

• Cleaning the air filter.

Oil Change

The oil on this engine should be changed after the first

10 hours of use and every 25 hours there after.

1. To change the oil in the AC3 engine you must

unscrew the oil fill plug in the crank case cover.

See Figure 2.1.

2. Drain oil into an approved container. Dispose of

oil in accordance with local regulations.

3. Fill the crankcase with 3.04 oz (90cc) of SAE 30

motor oil.

• The spark arrestor should be cleaned and the

valves should be adjusted at every oil change.

NOTE: The spark arrestor also serves to keep

blockages out of the exhaust system. Typical

blockages include insect nests built during the

dormant season.

Spark Arrestor

1. To clean the spark arrestor remove the engine

cover using a T-20 driver. See Figure 2.2.

2. Remove the two screws holding the spark arres-

tor cover in place with a T-25 driver.

See Figure 2.3.

Figure 2.1

Oil fill plug

metal sump

cover

Figure 2.2

Engine cover

Screws

Figure 2.3

Screws for

spark arrester

3. Inspect the spark arrestor. See Figure 2.4.

4. If it is blocked with carbon, remove it. It may be:

• Replaced

• Cleaned by mechanical means

• Solvent cleaned

• Burned clean using a butane or propane torch.

5. Reinstall the Spark arrestor screen and bolt

down the spark arrestor cover.

NOTE: Apply a thread locking compound such

as Loctite

266

to the long bolt (the one with

a hex head, it is the one closest to the other two

hex head screws) and torque it to 50-55 in. lbs.

(5.7-6.2 Nm). Hand tighten the short screw.

Figure 2.4

Spark arrestor screen

Spark Plug

To remove the spark plug:

1. Unplug the spark plug wire.

CAUTION: Do not grab the spark plug wire with

pliers. Damage to the sparkplug boot will result.

A damaged spark plug boot will weaken the

spark of the spark plug.

2. Unscrew the spark plug with a 5/8” spark plug

socket.

Valve Lash

1. To adjust the valves remove the valve cover with

a T-25 driver. See Figure 2.5.

2. Rotate the crank shaft to bring the piston to top

dead center of the compression stroke (valves

closed).

• Use the starter rope to turn the crank shaft.

• Use a probe in the spark plug hole to track the

piston position.

3. The valve clearance for this engine is .003”-

.006”(.08-.15 mm) for both valves.

Figure 2.5

Valve cover

4. Check the valve lash by placing a feeler gauge

between the rocker and the valve stem. To

adjust the valve loosen or tighten the fulcrum nut

with a 8mm wrench until there is a slight drag on

the feeler gauge when you pull it out.

See Figure 2.6.

5. Inspect the gasket that the valve cover sits on for

damage. If it is damaged or compressed replace

it.

6. Install the valve cover.

7. Replace the spark plug with a Champion

RDZ19H, gasket seat plug.

NOTE: Torque the spark plug to 100-110 in.

lbs.(11.3-12.4 Nm).

NOTE: The spark plug gap is .025”(.655mm).

8. Install the engine cover.

NOTE: There are six screws for the engine

cover, three that go into the engine block casting

and three that go into the starter housing. Make

sure you put the machine threaded screws into

the casting and the plastic threaded screws into

the starter housing. See Figure 2.7.

Air filter

The air filter should be cleaned and oiled after every 10

hours of use (depending on area of use, dusty areas

require more frequent cleanings).

NOTE: If the edger has a paper element air filter,

Do Not oil it.

Figure 2.6

Feeler gauge

Fulcrum nut

Rocker

Figure 2.7

Plastic threaded

screw

Machine threaded

screw

1. To reach the air filter remove the cover.

1a. Remove the air filter cover by pressing in

the tab on the side of the filter housing

and lifting the cover off. See Figure 2.8.

2. Pull the filter out. See Figure 2.9.

3. If the filter is crumbling or brittle replace the filter.

4. Wash the air filter with warm soapy water. Let

the filter air dry. DO NOT wring the filter out.

Wringing the filter can tear it. Squeeze the filter,

but do not twist it. Put a 1/4 teaspoon (1.25cc) of

oil to the filter and squeeze it through out the fil-

ter.

5. Test run the engine before returning it to service

Figure 2.8

Air filter cover

Press tab

Figure 2.9

Air filter

3. INITIAL TROUBLE SHOOTING

The first step in diagnosing an engine problem is to

perform the periodic maintenance. A majority of the

poor run or no start conditions will be solved just by

doing the required maintenance.

1. Drain and inspect the fuel:

•Look for water.

• Look for dirt.

• Look for discoloration.

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

• Save to show to customer.

2. Put fresh fuel in fuel tank.

3. Inspect the oil:

• Is there oil in it.

• What is the oil level?

• What type of oil is in it?

• If there is too much oil that could be a leaking

needle valve allowing gas to follow into the

engine.

• If the oil dirty, that would show poor maintenance

and possibly a worn engine.

• If the oil is low inspect the PCV valve for proper

operation.

• A PCV valve stuck closed will cause the engine

to smoke.

• A disconnected PCV valve will allow dirt into the

engine. See Figure 3.1.

Figure 3.1

PCV valve

4. Inspect the spark plug:

• What does the spark plug look like?

• A dry fowled plug could mean the engine is run-

ning rich.

• A wet fowled plug indicates the engine is burning

oil.

• A white coating on the plug would mean the

engine is running lean.

5. Inspect the air filter:

• What does the air filter look like? Dirt-blocked,

over-oiled, missing, wrong filter?

• Look for signs of dirt ingestion.

• A dirty air filter would restrict air flow.

• A missing air filter means that the engine has

ingested dirt that could damage the piston and

cylinder.

NOTE: Most gasoline engine diagnosis involves

isolating problems in the four critical factors an

engine needs to run properly:

• Ignition

- sufficient spark to start combustion in

the cylinder, occurring at the right time.

• 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.

•Fuel

- correct type and grade of fresh gasoline; in

sufficient quantity, atomized (tiny droplets) and in

correct fuel/air proportions.

•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.

6. To isolate the ignition system and compression

from the carburetor system:

6a. Prime the engine through the carburetor

throat using a squirt bottle.

6b. Verify that the engine stop switch is in the

engine run position. Most switches are

spring loaded to the run (1) position, but

some are not.

6c. Attempt to start the engine.

6d. If the engine starts and runs long enough to

burn the prime, the problem is effectively

isolated to the fuel system. proceed to the

Troubleshooting the Fuel System section

of this manual.

6e. If the engine fails to burn the prime, check

the compression.

6f. If compression is OK, check ignition system

as described in the Troubleshooting the

Ignition System section of this manual.

7. To perform a compression test:

NOTE: If the engine will run, start the engine and

let it warm up first for a better reading.

7a. Remove the spark plug.

7b. Screw the compression tester into the spark

plug hole.

7c. Pull the starter rope until the needle on the

compression gauge does not move any-

more.

7d. Read the gauge. See Figure 3.2.

NOTE: If the engine has less than 90 psi (6.2

bar) compression, the carburetor will not have

enough vacuum to draw fuel into the engine.

• The engine will have to be torn down to deter-

mine the cause of the low compression.

NOTE: If the engine has more than 125 psi (8.6

bar), the engine will not breath properly.

• Check the valve adjustment.

• Check for restrictions in the exhaust.

Figure 3.2

8. Check and adjust the valve lash by following the

procedures described in the section on periodic

maintenance.

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

4. TROUBLESHOOTING THE IGNITION SYSTEM

To test the ignition system:

1. Disconnect the spark plug wire.

2. Connect a spark tester to the spark plug wire.

3. Connect the other end of the spark tester to the

engine block. See Figure 4.1.

CAUTION: Never remove the spark plug and

hold it against the engine block to test for spark.

The fuel/air mix coming out of the spark plug

hole will catch on fire.

NOTE: The spark should be a minimum of 10 Kv

(10,000 volts) at pull over speed.

4. Pull the starter rope and watch the spark tester.

If sparks are seen in the spark tester, the ignition

system is working. Replace the spark plug.

• If no sparks are seen in the spark tester further

testing is required.

To test the module:

1. Remove the starter housing as described in the

“starter” section of this manual to expose the

module.

2. Check the air gap for the module. set it to .010

by following the steps described in the section

on the ignition system.

Figure 4.1

Spark tester

3. Disconnect the red wire. See Figure 4.2.

4. Install the starter as described in the “starter”

section of this manual.

5. Install the clutch as described in the ““clutch”

section of this manual.

6. Try to start the engine with the spark tester still

hooked up.

NOTE: If there is spark now, test the engine kill

switch and check the red wire for as short to

ground.

NOTE: If there still in no spark, hold a screw-

driver against the magnets on the flywheel to

feel if they are magnetic.

• If the magnets are good, replace the module. If

not replace the flywheel.

Test the engine stop switch:

1. Remove the grip by removing the six

screws with

a T-20 driver.

2. Disconnect the wires from the engine kill switch.

3. Connect an ohm meter or continuity light to the

switch.

4. With the switch in the engine run position (l), the

meter should indicate no continuity.

See Figure 4.3.

NOTE: Most stop switches are spring loaded to

the run position when it is released. this prevents

no-start situations caused by the customer fail-

ing to turn the switch on.

5. Hold the switch in the stop position (0). The

meter should indicate continuity. See Figure 4.4.

Figure 4.2

Disconnect the red wire

Figure 4.3

Switch in the engine

run position

Figure 4.4

NOTE: If the results are not as described, the

switch is bad and should be replaced.

6. If there is reason to suspect that the ignition tim-

ing is off:

6a. Remove the starter by following the steps

described in the section on starter

removal.

6b. Make sure the module air gap is correct by

following the steps described in the sec-

tion on the Ignition Repair.

6c. Inspect the pawls on the flywheel for dam-

age. Make sure they move freely.

6d. If the flywheel is damaged or the starter

pawls or sticking, replace the flywheel.

6e. Remove the flywheel.

6f. Inspect the flywheel key, If damaged

replace the key.

6g. Inspect the key way on the flywheel, if dam-

aged replace the flywheel.

6h. Inspect the key way on the crank shaft for

damage, if damaged short block the

engine.

7. Assemble and test run the engine before return-

ing it to service.

5. TROUBLESHOOTING THE FUEL SYSTEM

1. Drain and inspect the fuel:

•Look for water.

• Look for dirt.

• Look for discoloration.

• Sniff carefully to see if it smells like varnish or

oil.

• Save to show to customer.

2. Inspect the fuel filter. If it is dirty, replace it follow-

ing the steps described in the section on Fuel

System Repair in this manual. See Figure 5.1.

3. Inspect the fuel lines:

• Are they cracked?

• Are they clogged?

• Are they brittle?

• If the answer to any of the above is yes, replace

the fuel tank following the procedure described

in the section on the Fuel System Repair.

4. Test and inspect the primer bulb:

• Is it leaking or is it brittle?

• If so, replace the primmer bulb.

• Does it circulate fuel when pumped?

• If not, replace the primer.

5. If compression, ignition and fuel supply are OK,

but it does not run with fresh fuel repair/replace

the carburetor as described in the Carburetor

Repair section.

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

Figure 5.1

Fuel filter

6. TROUBLESHOOTING/REPAIRING THE CAR-

BURETOR

Typically, troubleshooting the carburetor is the last step

in the diagnostic process. The other factors are more

readily identified; spark vs. no spark, Specific pressure

readings on a compression gauge, or a visible block-

age in the muffler. Carburetor function is more subtle.

While specific problems with a carburetor can be identi-

fied on tear-down, identification of the carburetor as the

location of the problem is usually done by process of

elimination.

To troubleshoot the carburetor:

1. Inspect and clean the vent under the primer

body for debris. See Figure 6.1.

2. If the carburetor is running lean:

• Inspect the carburetor spacer for cracks.

• Inspect the spacer gasket.

NOTE: A cracked spacer or a leaking gasket

between the spacer and the cylinder could result

in a lean run or prevent the impulses from the

engine from driving the fuel pump.

See Figure 6.2.

3. Disassemble the carburetor. See Figure 6.3.

Figure 6.1

Primer body

Vent hole

Primer check

valve

Primer bulb

Figure 6.2

Gasket

Spacer

Figure 6.3

4. Inspect the throttle valve assemble for debris

and freedom of movement. See Figure 6.4..

5. If there is a problem with the throttle valve

assembly, check on availability and price of parts

to determine if the carburetor should be repaired

or replaced.

Disassemble the carburetor:

1. Inspect the diaphragms. If torn, damaged or brit-

tle install a diaphragm kit.

2. Inspect for dirt or varnish build up inside the car-

buretor. If there is a lot of dirt/varnish in the car-

buretor, replace it.

3. Check that the needle valve is set to the right

height. See the carburetor manufacturer for the

proper procedure.

4. Inspect the needle valve and seat.

5. If the seat is damaged, replace the carburetor.

6. If there is a minor amount of dirt/varnish in the

carburetor or debris and/or damage to the nee-

dle valve, install a rebuild kit.

To rebuild/repair a carburetor:

1. Remove the air filter housing as described in the

section on the fuel system.

2. Carefully remove the two fuel lines.

Figure 6.4

Throttle valve assembly

3. Disconnect the throttle cable by unhooking the

Z-fitting. See Figure 6.5.

4. Place the carburetor in a clean area on the work

bench.

5. Remove the four screws going through the

primer bulb housing with a #0 phillips screw-

driver.

6. Separate the carburetor, placing each part on

the bench in the order they came apart.

See Figure 6.6.

Figure 6.5

Unhook the

Z-fitting

Figure 6.6

7. Inspect the metering valve and the metering

valve seat for dirt and/or pitting. See Figure 6.7.

NOTE: If the metering valve seat is damaged

replace the carburetor. See Figure 6.8.

8. Inspect the Metering valve body, primer pump

body and the ventri housing for dirt and/or var-

nish.

NOTE: If there is a minor amount of dirt/varnish

in the carburetor it would be worth while to clean

and rebuild the carburetor by following the pro-

cedures recommended by the carburetor manu-

facturer.

NOTE: If there is a lot of dirt/varnish in the car-

buretor, replace the carburetor.

9. Clean the ventri and the metering valve hous-

ings.

10. Inspect the diaphragms for brittleness and/or

damage.

NOTE: The carburetor used in this manual is a

Walbro. Depending on the application the

engine may have a different carburetor. All car-

buretors have a manufacturer name cast on

them. It is advisable to contact the carburetor

manufacturer for the proper rebuild procedure.

11. Remove the throttle valve assembly.

See Figure 6.9.

12. Clean the metering orifice with carb cleaner.

CAUTION: Do not insert anything into the orifice

to clean it. That will damage the orifice resulting

in the carburetor being unrepairable.

See Figure 6.10.

Figure 6.7

Inspect for dirt or damage

Figure 6.8

Needle valve

seat

Figure 6.9

Throttle valve assembly

Idle stop

screw

Figure 6.10

Orifice from the

Venturi side

13. The orifice can also be seen from the pump side

of the throttle housing. See Figure 6.11.

14. The fuel pump in the carburetor is driven by vac-

uum pulses in the intake port. The impulse port

from the spacer lets the vacuum pulses into the

pump camber. See Figure 6.12.

15. Make sure this port is clean and free of debris.

16. Reinstall the Throttle valve assembly.

Figure 6.11

Orifice

Pump spring

Figure 6.12

Impulse port

Vent through metered

orifice to atmosphere

17. Set the needle valve lever as per the carburetor

manufacturer’s recommendations using a W-

tool. See Figure 6.13.

18. There are ports in the metering valve body. it is

important to make sure they are clean and free

of debris. See Figure 6.14.

19. Follow steps in reverse order to rebuild the car-

buretor.

20. Set the needle valve to the manufacturers’

specifications

21. Preform a needle valve pop off test by following

the carburetor manufacturer’s recommenda-

tions.

22. Install the carburetor on the engine.

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

Figure 6.13

Needle valve lever

Figure 6.14

The lines show the

paths of the different

ports

Filter screen

7. BLADE AND BELT

Blade removal/replacement

1. Remove the blade retaining nut with a 15/16”

socket and an impact wrench. See Figure 7.1.

NOTE: Production units may have a hex milled

into the spindle shaft to allow use of an allen

wrench to hold the shaft while removing the

blade.

2. Install the blade by following the above step in

reverse order.

Belt removal/replacement

1. Remove the blade as described above.

2. Remove the three screws holding the blade

guard in place using a T-40 Torx driver.

See Figure 7.2.

NOTE: The spindle hub will Come off with the

blade guard.

3. Remove the spindle pulley cover by removing

the three screws using a 3/8” wrench.

See Figure 7.3.

Figure 7.1

Blade retaining nut

Figure 7.2

Remove these three screws

Figure 7.3

Remove these three screws

4. Remove the belt cover by removing the three

screws using a T-20 Torx driver. See Figure 7.4.

5. Remove the belt guide using a 3/8” wrench.

See Figure 7.5.

Figure 7.4

Remove these three

screws

Figure 7.5

Belt guide

6. Remove the spindle pulley. See Figure 7.6.

7. The belt will now slide off.

8. Install belt by following the above steps in

reverse order.

Figure 7.6

Spindle pulley

8. STARTER REMOVAL

1. Remove the belt cover and belt following the

steps described in the Belt and Blade section.

2. Remove the spark plug.

3. Insert a long length of rope into the cylinder to

block the engine.

4. Remove the engine pulley using a 1” wrench.

See Figure 8.1.

5. Remove the three screws that go through the

frame in to the starter housing. See Figure 8.2.

6. The entire engine will now come off of the edger.

7. Remove the screws that hold the engine cover

to the starter housing. See Figure 8.3.

8. Remove the four screws in the front of the starter

housing. See Figure 8.4.

9. The starter will now slide off.

NOTE: If just the starter just needs a new starter

rope you can replace the rope; otherwise it is

more economical to replace the whole starter

housing assembly.

Figure 8.1

Engine pulley

Figure 8.2

Remove these three screws

Figure 8.3

Remove these

screws

Figure 8.4

screws

Starter housing

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MTD AC3 Series Shop Handbook

MTD AC3 Series Shop Handbook

MTD AC3 Series Shop Handbook

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