Service Manual
NOTE: These materials are for use by trained technicians 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 inexperienced 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 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
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. © Copyright 2005 MTD Products Inc. All Rights Reserved.
TROY-BILT CHAIN SAW - MODEL FS55 TB 4920CC
MTD Products LLC - Product Training and Education Department
FORM NUMBER 769-01423
9
/2004
Table of Contents
General Information .............................................................................................. 1
Air Filter ................................................................................................................1
Fuel Filter ............................................................................................................. 2
Chain Oil Filter ...................................................................................................... 2
Spark Arrester Screen .......................................................................................... 3
Spark Plug ........................................................................................................... 4
Bar and Chain Removal ....................................................................................... 5
Clutch Removal .................................................................................................... 5
Chain Oiler Removal ............................................................................................ 6
Starter Assembly Removal ................................................................................... 8
Servicing the Spring Assist Starter ....................................................................... 8
Flywheel Removal ................................................................................................ 9
Handle Removal ................................................................................................. 10
Carburetor Adjustment ....................................................................................... 12
Carburetor Removal ........................................................................................... 12
0
Troy-Bilt Chain Saw
Model FS55 - TB4920CC
TROY-BILT CHAIN SAW - MODEL FS55 TB 4920CC
GENERAL INFORMATION
• 55cc Displacement - Family 4MHXS.0555AA
EM
• The Troy-Bilt models are all AV - Anti-Vibration.
cedures for proper setup and operation.
IMPORTANT: Prior to servicing the chain saw,
remove the spark plug wire from the spark plug.
WARNING : Never perform maintenance when
the engine is hot, to avoid any chance of burning
hands or fingers.
1. AIR FILTER
1.1. Using a T-25 Torx Driver, loosen the cover
retaining screws. Lift off the cover. See Figure 1.
Cover Screws
• This engine conforms to 2004 U.S. EPA PH 2
Emission Regulations.
• 20” Blade w/ INTENZ by Oregon. Incorporates
chain tension adjustment on the blade bar. Bar #
9040-31B203
• Chain # 9220-31B203 (20”-78DL)
THIS SAW FEATURES OUR SPRING ASSIST
STARTING SYSTEM.
• The system allows the customer to pull the recoil
rope at any pace they please, yet still generate
enough force to start the engine.
• The system is simple; it consists of a recoil pulley assembly, which includes an accumulator
spring. As the rope is pulled, the accumulator
spring winds up. When the force on the accumulator spring over-comes the engine compression, it releases its accumulated energy,
spinning the crankshaft rapidly.
This Service Manual is a supplement to the Operator’s Manual. Read, understand and follow all
safety procedures before operating or servicing
this chain saw. Refer to the Owners Manual for pro-
Figure 1
1.2. Remove the air filter. See Figure 2.
Filter
Figure 2
1
1.3. Wash filter in clean, warm, soapy water. Rinse in
clear, cool water. Air dry completely. See Figure
3.
2.4. Disconnect filter and discard.
NOTE: Do not pull hose completely out of tank.
2.5. Install a new fuel filter on hose and pull hose/filter assembly back into tank so filter is positioned
in front right corner.
2.6. Reconnect fuel hose to carburetor fitting.
2.7. Replace air filter and air box cover.
3. CHAIN OIL FILTER
NOTE: If the chain oiler fails to work properly,
the cause may be a clogged filter. Drain oil tank
before changing filter.
NOTE: Make sure you have a new filter and a
length of hose before beginning this procedure.
Figure 3
NOTE: It is advisable to have a supply of spare
filters.
1.4. Install air filter.
1.5. Install engine / air filter cover. Make sure cover
fits properly.
1.6. Tighten the cover retaining screws securely.
2. FUEL FILTER
2.1. Remove air box cover and air filter.
2.2. Disconnect fuel hose from the carburetor fitting.
NOTE: You may not need to disconnect the fuel
hose to gain access to the filter.
2.3. Pull fuel filter out of tank with a bent wire or long
needle nosed pliers. See Figure 4.
3.1. Using a T-25 Torx driver, remove the two screws
securing the lower heat shield to the crankcase.
See Figure 5.
Tor x S c r e w s
Figure 5
Fuel Filter
Figure 4
2
3.2. Using a small screwdriver or needlenose pliers,
disconnect oil hose from the pump fitting. See
Figure 6.
Oil Hose
3.5. Tip the saw over the oil filler or use a wire with a
hook to remove the oil filter from tank. See Figure 8.
Oil Filter
Figure 6
3.3. Using a side cutter, cut the hose as close to the
side of the oil reservoir as possible. See Figure
7.
Figure 7
3.4. Using a small screwdriver, push the end of the
tube into the oil reservoir.
Figure 8
3.6. Insert a long length of new hose into the tank
from the crankcase side and push it into the
tank.
3.7. Use a hook to fish the end of the hose through
filler opening.
3.8. Install a new filter on the hose end and pull hose
back into tank so the filter is positioned in the
bottom of tank.
3.9. On the crankcase side, put a loose bend in the
hose and cut it so that it fits on the end of the oil
pump fitting without kinking.
4. SPARK ARRESTER SCREEN
NOTE: A clogged spark arrester screen will dra-
matically reduce engine performance.
3
4.1. Using a screwdriver or drift punch and hammer,
flatten the tabs on the lock plate of the muffler
assembly. See Figure 9.
5.1. Push STOP switch up.
5.2. Remove top Cover.
5.3. Disconnect the wire connector from the spark
plug by pulling and twisting at the same time.
Tab s
Figure 9
4.2. Using a 10mm socket, remove the two muffler
retaining nuts, lock plate and muffler cover.
4.3. Remove the spark arrester screen from the
metal baffle. Replace the screen with a new one.
See Figure 10.
Muffler Spark Arrester Baffle
5.4. Using a scrench, remove the spark plug. DO
NOT USE ANY OTHER TOOL. See Figure 11.
Scrench
Figure 11
5.5. Check electrode gaps with wire feeler gauge and
set gaps to .025" (.635mm) if necessary or install
a new spark plug.
NOTE: A resistor spark plug must be used for
replacement (part no. 9295-320001).
Figure 10
4.4. Reassemble the muffler components and tighten
nuts securely.
4.5. Bend the tabs on the lock plate to secure the hex
nuts.
5. SPARK PLUG
NOTE: For efficient operation of the engine, the
spark plug must be kept clean and properly
gapped.
NOTE: This spark ignition system meets all
requirements of the Canadian InterterenceCausing Equipment Regulations.
4
6. BAR AND CHAIN REMOVAL
7.3. Remove the spark plug.
6.1. Using a scrench or 5/8” socket, remove the two
nuts securing the Chain Brake Assembly to the
unit. Remove the assembly. See Figure 12.
Hex Nuts
Figure 12
6.2. Use the scrench or a screwdriver to loosen the
chain tension adjustment ½ turn counterclockwise to take tension off the chain. See Figure 13.
7.4. Place a length of starter cord in the spark plug
opening to ease removal of the clutch/drum
assembly. See Figure 14.
Starter Cord
Figure 14
7.5. Using a 13mm socket, remove the compression
nut securing the Clutch/Drum assembly to the
crankshaft. See Figure 15.
Chain Adjustment
Figure 13
6.3. Remove the chain from around the bar and slide
the bar and chain guide plate from the mounting
studs.
7. CLUTCH REMOVAL
7.1. Remove the chain brake assembly, bar and
chain. See BAR AND CHAIN REMOVAL Section.
7.2. Remove the air filter cover.
Compression Nut
Figure 15
NOTE: The nut is left hand threaded. Turn the
socket clockwise to loosing it.
5
7.6. Remove the clutch/drum sprocket assembly
from the crankshaft.
NOTE: There is a needle bearing on the crankshaft the may stay on the shaft or come out with
the clutch. See Figure 16.
Clutch Drum Stamped Washer Tangs Clutch
8. CHAIN OILER REMOVAL
8.1. Perform all steps to remove the clutch/drum
sprocket assembly. Refer to CLUTCH
REMOVAL Section.
NOTE: There is an adjustment screw for changing the flow of chain oil accessible from under
the saw near the drum sprocket. See Figure 17.
Figure 16
NOTE: There is a stamped washer between the
drum sprocket assembly and the housing. Note
the orientation of this washer. The cupped side
faces in and the tangs mate with the chain
sprocket. See Figure 16.
NOTE: The notches in the sprocket need to
mate with the tabs on the chain oiler pump.
Adjustment Screw
Figure 17
8.2. Using a T-15 Torx driver, remove the small screw
securing the flange plate and bar plate to the
housing. Set the screw, plate flange plate and
bar plate aside. See Figure 18.
Screw Flange Plate
Figure 18
6
8.3. Using a T-25 Torx driver, remove the 3 screws
securing the pump assembly to the housing. See
Figure 19.
Pump Screws
Figure 19
NOTE: The top right screw is longer then the
other two.
8.5. Secure the clear oil feed tube going to the pump
with some form of clamp or tie to keep it from
dropping into the oil reservoir when you remove
the tube from the pump. See Figure 21.
Rubber Band
Figure 21
8.6. Remove the tube from the pump assembly.
8.4. Pull the pump slightly away from the housing.
The upper oil feed should release from the slot in
the housing. See Figure 20.
Upper Oil Feed
Figure 20
8.7. Remove the chain oiler pump from the unit. See
Figure 22.
Figure 22
7
8.8. Remove the foam plug at the rear of the pump.
See Figure 23.
Pump Housing
Foam Plug
“O” Ring
Washer
Spring
Adjustment Screw Pump Piston Gear
9.2. Remove the starter assembly from the unit. See
Figure 25.
Figure 23
8.9. Remove the flow set screw from the pump.
8.10. You can now slide the pump assembly components from the pump housing. Notice how the
set screw affects the depth of the pump piston
and adjusts the oil quantity. See Figure 23.
NOTE: Replace the “O” ring and felt washer during service of the pump.
9. STARTER ASSEMBLY REMOVAL
9.1. Using a T-25 Torx driver, remove the four screws
securing the starter assembly to the housing.
See Figure 24.
Figure 25
10. SERVICING THE SPRING ASSIST STARTER
The spring assist starting system contains two coiled
torsion springs. The standard recoil spring is used
strictly to retract the starter rope. In addition to the
recoil spring there is an accumulator spring located
between the starter rope pulley and the clutch dog
assembly. When the starter rope is pulled the clutch
dogs engage the flywheel. The flywheel resists turning
because of engine compression. As tension in the
accumulator spring increases it overcomes the engine
compression and rapidly turns the crank and starts the
engine.
Tor x S c r e w s
Figure 24
NOTE: The upper screw is a machine screw and
uses locktite to secure it.
8
10.1. To service the starter, use a T-25 Torx driver to
remove the screw securing the pawl mechanism
and starter cord pulley to the housing cover. See
Figure 26.
Screw
10.3. Inspect componants. See Figure 28.
Cord Return Spring
Pawls
Figure 26
10.2. Note the orientation of the parts. See Figure 27.
Cord Pulley Washer Spring
Plate (Do not reverse)
Figure 27
NOTE: If the cover plate is reversed on the
assembly, the pawls won’t move out and the
starter will not work properly.
Figure 28
10.4. Remove the accumulator spring cover and
inspect the spring. See Figure 29.
Accumulator Spring Spring Slot
Figure 29
10.5. During assembly, feed the pull cord through the
housing cover, knot the cord as shown in the picture and wind the cord around the starter pulley.
Place the pulley under spring tension for the last
two turns.
11. FLYWHEEL REMOVAL
11.1. Remove the starter assembly following the
STARTER ASSEMBLY REMOVAL Section.
9
11.2. Using a 13 mm socket, loosen but do not
remove the nut securing the flywheel to the drive
shaft. See Figure 30.
Figure 30
11.3. Loosen the nut until the threads are flush with
the end of the drive shaft.
11.4. Place a pry bar between the flywheel and the
case.
11.5. Put pressure on the flywheel while tapping the
nut with a brass drift and a hammer. See Figure
31.
11.6. The flywheel is keyed to the tapered drive shaft.
See Figure 32.
Keyway
Key in tapered Shaft
Figure 32
NOTE: Make sure you do not displace the key
during assembly.
11.7. Assemble in reverse order of disassembly.
NOTE: Use a feeler guage to properly gap the
distance between the coil and flywheel. It should
be between .08”-.010” tolerence. See Figure 33.
Feeler Guage
Pry Bar
Brass Drift
Figure 33
Figure 31
12. HANDLE REMOVAL
NOTE: If the throttle cable breaks, it will be nec-
essary to remove the handle to service it.
NOTE: It will also be necessary to remove the
handle in order to remove the caruretor from the
unit.
10
12.1. Using a T-25 Torx driver, remove the lower left
handle mounting screw. See Figure 34.
12.3. Remove the screw at the top right side of the
kick back lever. Remove the handle from the
unit. See Figure 36.
Mounting Screw
Figure 34
12.2. Remove the mounting screw at the left side of
the baseplate. See Figure 35.
Mounting Screw
Figure 35
Mounting Screw
Figure 36
NOTE: Note any different length or type of
screws used during disassembly.
NOTE: Note the routing of the throttle cable and
electrical wires.
12.4. To service the throttle control, power switch or
other handle componants, remove the five
screws securing the handle halves together. See
Figure 37.
Mounting Screws
11
Figure 37
NOTE: Note any different length of screws used
during disassembly.
12.5. Separate the handle halves. Note the orientation
on all componants of the handle during diassembly. See Figure 38.
14.6. Using a T-25 Torx driver, remove the three
screws securing the cover assembly to the fuel/
oil tank assembly. Remove the cover. See Figure 39.
Safety
Trigger
Throttle
Cable
Figure 38
NOTE: During handle assembly be sure to place
the wire cable assemblies in front of the springs.
13. CARBURETOR ADJUSTMENT
The carburetor was pre-set at the factory for optimum
performance. Only qualified technicians should adjust
the fuel/air mixture. If the carburetor becomes gummed
up or fails in any way it can be replaced or rebuilt.
Tor x S c r e w s
Figure 39
14.7. Using a T-25 Torx driver, remove the screw
securing the ground wire to the cylinder body.
See Figure 40.
Ground Wire
Ignition Lead
Cable Guide
14. CARBURETOR REMOVAL
14.1. Remove air filter cover.
14.2. Remove starter assembly cover.
14.3. Disconnect spark plug wire.
14.4. Remove the air filter.
14.5. Remove the spark plug.
Figure 40
14.8. Using a T-25 Torx driver, remove the cable guide
attached to the cylinder body. See Figure 40.
14.9. Disconnect the lead attached to the ignition
assembly. See Figure 40.
14.10.Using a T-25 Torx driver, remove the 3 screws
securing the handle assembly to the unit. See
HANDLE REMOVAL Section.
NOTE: On the right handle and rear handle
there is a cable assembly that attaches between
12
the handle and the spring. Be sure to assemble
correctly. See Figure 41.
Cable Assembly
Figure 41
14.11. Remove the two wire leads from the housing
groove as you separate the handle from the
housing. See Figure 42.
14.12.Using a small screwdriver, pry the rubber seal
from above the flex conduit. Set it aside. See
Figure 43.
Rubber Seal
Figure 43
14.13.Using a small screwdriver, pry the flex conduit
from the carburetor pulse inlet. See Figure 44.
Wire Leads
(Notice Routing)
Figure 42
NOTE: The throttle cable will still be attached to
the carburetor at this time. It will be disconnected later.
Flex Conduit
Figure 44
13
14.14.Using a T-25 Torx driver, remove the two screws
attaching the carburetor to the intake housing.
See Figure 45.
14.17.As you remove the carburetor, remove the choke
assembly and note the orientation of the small
wire connector going from the choke to the carburetor. Set the choke assembly and connector
wire aside. See Figure 47.
Tor x S c r e w s
Figure 45
NOTE: You will need to flex the carburetor
upward at the rear to access the screws.
14.15. Slip the carburetor up and out of the housing.
See Figure 46.
Fuel Line
Choke Wire
Choke Assembly
Figure 47
14.18.Slip the throttle cable from its seat and remove
the “Z” fitting from the throttle lever.
14.19.Remove the air cleaner boot and two screws
from the carburetor.
14.20.Remove the lower black primer hose from the
carburetor. See Figure 48.
Primer Hose
Figure 46
14.16.Using a small flat bladed screwdriver, remove
the fuel line. See Figure 46.
Figure 48
14
14.21.The carburetor can now be rebuilt or replaced.
See Figure 49.
Figure 49
14.22. Install the carburetor in the reverse order of disassembly.
15
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