Workshop manual
343R , 345RX
343F, 345FX, 345FXT
English
Workshop Manual
Brushcutter, Trimmer
Model 343R, 345RX, 343F, 345FX, 345FXT
Contents
General recommendations ___________________ 2
1. Starter __________________________________ 3
2. Electrical system _________________________ 7
3. Fuel system _____________________________ 15
4. Centrifugal clutch ________________________ 31
5. Angle gear ______________________________ 37
6. Cylinder and piston ______________________ 41
7. Crankshaft and crankcase _________________ 51
©
Copyright Husqvarna AB, Sweden 2003
1
General recommendations
Remember:
Never start the engine without the clutch and clutch drum
!
mounted.
Do not grasp hot elements such as the muffler or the clutch
!
before they have cooled sufficiently to avoid burn injuries.
Avoid getting petrol on you skin or in your mouth. Use
!
protective cream on your hands. This lowers the risk of
infection and makes dirt easier to wash off. Long-term
contact with engine oil can be damaging to your health.
Never run the engine indoors. The engine exhaust is poisonous!
!
Wipe up any spilled oil from the floor immediately in order to
!
avoid injuries from slipping.
Do not use tools that are worn or fit poorly on nuts and bolts
!
and so on.
+ Always work on a clean work surface.
+ Always work in a logical manner in order to be sure that all
components are correctly attached and that nuts and bolts
are tightened.
+ Use special tools where recommended in order to work
correctly.
Fire risk
Handle petrol with respect, since it is highly flammable.
Do not smoke and ensure that there are no open flames or
sparks in the vicinity.
Make sure that there is a functioning fire extinguisher in the
vicinity.
Do not try to extinguish a petrol fire with water.
Poisonous fumes
When using cleaning fluids, read the instructions carefully.
Make sure that ventilation is good when handling petrol, trichloroethylene and other highly volatile liquids.
The engine exhaust is poisonous. Test run the engine only if
ventilation is good. Preferably outside.
Special tools
Certain tasks in this handbook require the use of special
tools. In sections where this is applicable, an image of the
tool with an ordering number is provided.
We recommend using special tools in order to avoid personal
injury and to eliminate expensive damage to the components
in question.
502 51 03-01
Sealing faces and gaskets
Make sure that all sealing faces are clean and free from old
gasket remnants. Use a tool that will not damage the sealing
face when it is cleaned. Any scratches and irregularities
should be removed with a fine, float-cut file.
Sealing rings
Always change a sealing ring once it has been dismounted.
The sensitive sealing lips can be easily damaged with poor
sealing ability as a result. The surfaces that the seal is to
tighten against must also be completely free from damage.
Lubricate the sealing lip with grease before it is attached and
make sure that it is not damaged by such things as the
collars and splines on an axle. Use tape or a conical bushing
as protection. It is important that the sealing ring is turned
correctly in order for it to function as intended.
!
2
WARNING!
Risk of personal injury if the instructions are not
followed.
NOTE!
Material damage may occur if the instructions are
not followed.
Starter
1.
1
Contents
Dismantling _________________________________ 4
Assembly __________________________________ 5
Replacing the drive dogs ______________________ 6
3
1
!
Starter
WARNING!
Protective glasses should be worn when working on the starter to avoid injury to the eyes if, for
some reason, the return spring should fly out.
Dismantling
Remove the starter from the engine.
502 50 18-01
Loosen the spring tension. Loosen the spring tension.
Dismantling
Remove the 4 bolts and lift off the
starter.
The cylinder cover does not need to be
loosened or detached.
Pull out the starter cord about 30 cm.
Brake the starter pulley with your thumb
and lift the cord as illustrated.
Let the starter pulley rotate backwards
slowly.
Remove the bolt in the centre of the
starter pulley and remove the starter
pulley.
4
Remove the bolt in the centre of the
starter pulley. Lift the starter pulley
carefully from the starter cover.
Starter
1
Remove the spring cassette.
WARNING!
!
Wear protective glasses. The return spring can fly out
and cause personal injury if improperly handled.
Assembly
Clean requisite parts and assemble in
the reverse order as set out for dismantling.
NOTE!
Be careful when opening the packaging with the return spring so that the
spring does not fly out.
Remove the two bolts holding the
spring cassette and remove the
cassette for replacement if necessary.
Assembly
Clean all components before assembly:
Change return springs, starter pulley
and starter cord as needed.
Attach the spring cassette.
Attach the starter pulley.
Attach the new starter cord.
NOTE!
New starter cords can be attached without dismantling the starter!
Anchor the cord in the starter handle. Thread the cord through the starter
Attach the spring cassette and tighten
the two bolts (A).
Lubricate the bearing journal with a little
grease and attach the starter pulley.
Place the washer in place and tighten
the bolt.
Attach the new starter cord. Push it in to
the starter pulley’s track as illustrated and
then out through the cord guide in the
starter cover. Make sure that the knot at
the end of the cord is as small as possible!
handle and anchor it with a knot.
Fold down the free end and pull the
knot well into the handle.
5
1
Starter
Tighten the return spring.
Check the spring tension.
Mount the starter onto the engine. Mount the starter onto the engine.
Tighten the return spring.
Lift up the starter cord when the return
spring is completely loose and the cord
pulled out completely.
Then turn the starter pulley
clockwise
Check the spring tension. With the cord
completely pulled out the cord pulley
should be able to be turned at
another half revolution.
Pull out the starter cord a little.
Place the starter in position and release
the starter cord at the same time.
Check that the ignition cable is not
trapped (see arrow).
Check that the drive dogs grip the
starter pulley in the correct way.
Tighten the bolts.
7 revolutions.
anti-
least
Replacing the drive
dogs
See chapter 2 Ignition system.
Replacing the drive
dogs
See chapter 2 Ignition system.
6
Electrical system
2.
2
Contents
Checking the ignition spark ____________________ 8
Replacing the spark plug cover ________________ 10
Dismantling ________________________________ 11
Drive dogs _________________________________ 12
Assembly _________________________________ 12
Heated handles_____________________________ 12
7
2
The engine is equipped with an electronic ignition system completely without moving parts. Consequently, a faulty component cannot be repaired, but must be replaced by a new component.
The spark in an electronic ignition system has a very short burn time and can therefore be interpreted as
weak and can be difficult to see while troubleshooting.
Electrical system
Checking the ignition
spark
Clean the electrodes and check the
electrode gap.
502 51 91-01
If the electrodes are worn more than
50% the spark plug should be
changed.
Checking the ignition
spark
Remove the spark plug and clean it
from soot deposits with the help of a
steel brush.
Check the electrode gap. It should be
0.5 mm.
Adjust the gap as needed to the correct
value with the side electrode.
If the electrodes are worn more than
50% the spark plug should be changed.
Too large a spark gap entails a great
deal of stress on the ignition module
and risk for short-circuiting.
Check if a spark occurs when attempting to start.
Test with test spark plug no. 502 71 1301 if no spark is seen.
502 71 13-01
8
Also check that the stop switch is in the
start position.
Earth the spark plug on the cylinder
and pull sharply on the start handle.
A spark should be seen between the
electrodes.
If no spark is seen test with test spark
plug no. 502 71 13-01.
If a spark then occurs, the spark plug is
faulty.
Try a new spark plug.
Electrical system
2
If no spark occurs, disconnect the stop
switch.
Replace the switch if necessary
The stop switch can be easily detached
with a screwdriver.
If no spark occurs even now, remove
the short-circuit cable from the connection point in the carburettor compartment.
If the plug now sparks, the fault is either
in the stop switch or the short-circuit
cable.
Change the switch as needed and
check to see if the cable insulation is
damaged.
The stop switch is easily reached when
the cover is removed.
Use a screwdriver pinch the switch’s
snap fastener inside the throttle.
Still no spark?
Check the ignition cable’s connection to
the spark plug cover.
Still no spark?
Check other cables and connections.
Still no spark?
Check the spark plug connection.
Remove the spark plug cover and make
sure the ignition cable is not damaged.
Remove a segment of cable if required
to get sufficient contact at the connection coil.
Still no spark?
Check other cables and connections
for poor contacts (dirt, corrosion, cable
breakage and damaged insulation).
Make sure that the cables are correctly
drawn and lie in the cable grooves.
Do not forget to check the cables in the
throttle too.
See chapter 3 “Throttle”.
Tip!
Use an Ohmmeter in order to easily
check if cable breakage has occurred,
due to pinching, for example.
9
2
Electrical system
Still no spark?
Check the air gap.
0.3
502 51 34-02
Adjust the air gap. Adjust the air gap as needed to the
Still no spark?
Check the air gap between the flywheel
magnet and the ignition module. The
gap should be 0.3 mm.
Use a 502 51 34-02 feeler gauge.
correct value.
• Loosen the bolts.
• Position the feeler gauge and press
the ignition module against the
flywheel.
• Tighten the bolts and check the air
gap again.
If the spark plug still does not fire, the
ignition system should be replaced.
Replacing the spark
plug cover
1. Insert the ignition cable through the
spark plug cover.
2. Make a hole in the ignition cable for
the ignition coil.
502 50 06-01
3. Attach the ignition coil to the ignition
cable.
NOTE!
It is important that the tip of the ignition coil hits the centre of the
ignition cable to prevent sparking.
Replacing the spark
plug cover
1. Lubricate the ignition cable with a
little grease and thread it through
the spark plug cover.
2. Cut off a bit of the ignition cable
(approx. 5 mm) and make a hole in
the cable for the ignition coil with
the aid of a pair of no. 502 50 06-01
pliers.
3. Attach the ignition coil to the ignition
cable and ensure that the wire is
folded along the cable.
4. Pull the ignition coil into the spark
plug cover.
10
Electrical system
2
Dismantling
Remove the starter, cylinder cover, and
spark plug.
Attach piston stop no. 502 54 15-01.
502 54 15-01
Remove the nut holding the flywheel.
Dismantling
Remove the starter, cylinder cover, and
spark plug.
Fit piston stop no. 502 54 15-01 in the
spark plug hole.
NOTE!
Place the piston stop so it is
caught between the piston and
the cylinder head. Not so it sticks
out into the exhaust port.
Remove the nut holding the flywheel.
Remove the flywheel.
502 51 94-01
Remove the ignition module and the
generator.
Remove the flywheel from the crankshaft using punch no. 502 51 94-01.
Leave a gap of approx. 2 mm between
the punch and the flywheel.
Gently knock the punch with a hammer
while holding the flywheel with your
other hand.
Dismantle the ignition module.
Remove the ignition cable from the
holder (A).
Remove both bolts (B).
Loosen the short-circuit cable (C) from
the ignition module.
Remove the generator (D) that supplies
power to the heated handles.
502 50 18-01
11
2
Electrical system
Drive dogs
Remove the bolts.
Remove the hooks and the springs to
replace them.
Mind the washer (A) so as not to lose it.
Replace damaged parts.
Assemble in the reverse order.
502 50 18-01
Assembly
Check the key groove in the crankshaft
and key in the flywheel. If damaged the
components must be replaced.
Attach the ignition module and then the
flywheel.
Check the air gap, see page 9.
0.3
Drive dogs
The drive dogs can be easily replaced if
they are damaged.
Remove the bolts, the hooks and the
springs.
Mind the washer (A) so as not to lose it.
Replace damaged parts.
Assemble in the reverse order.
Check that the hooks can be turned
freely when the bolts are tight.
Assembly
Check that the key groove in the
crankshaft is not damaged. If it is, the
crankshaft must be replaced.
Attach the ignition module and make
sure the short-circuit cable is not
trapped.
Check that the key in the flywheel is not
damaged. If it is, the flywheel must be
replaced.
Attach the flywheel.
Check the air gap, see page 9.
502 51 34-02
Heated handles
The heating element in the handles consists of ceramic plates. These are self-regulating with regard to temperature. When temperature increases, the resistance in the
elements lowers and so does the temperature. So no separate thermostat is needed.
Remove the throttle from the handle.
In order to have access, the bolt that
holds the throttle and the cover with the
circuit breaker must be removed to
reach the electrical cables.
502 50 18-01
The heating element in the throttle is
accessed when the throttle lock is
pushed out of the throttle.
Pry off the locking catch and lift out the
heating element.
Remove the throttle from the handle.
See also chapter 3 “Throttle”.
In order to remove the heating element
the bolt (A) that holds the throttle and
cover (B) and the heater switch must
first be removed (2 bolts).
A heating element is placed in the
throttle lock for involuntary throttling.
Press the locking catch from the
throttle, making sure not to lose the
spring (A).
Pry off the locking catch (B) and lift out
the heating element (C).
12
NOTE!
Do not pry off the heating element
before the locking catch has been
removed. The element can be
damaged.
Electrical system
2
Separate the contacts (A-A) and (B-B).
Then extend the cables (A) and (B) with
approx. 90 cm long steel wires attached
to the contacts.
Remove the bolt and pull off the left
grip from the handle.
Pull one cable at a time from the
handle.
Remove the heating element from the
handle with a pair of flat nosed pliers.
Separate the contacts (A-A) and (B-B).
Then extend the cables (A) and (B) with
approx. 90 cm long steel wires attached
to the contacts.
This is to make it easier to draw the
cables to the new heating element back
through the handle.
1 = black
2 = blue
Remove the bolt that holds the left grip
on the handle.
Pull out handle from the handlebars
and then the cables, carefully and one
at a time, so that the steel wire does not
loosen from the cables.
The heating element is located in a
pocket in the outside of the handle.
Use flat nose pliers to pull out the
heating element from the handle.
NOTE!
Do not pull the cables or their
connections. Connections can be
easily broken.
Assemble in the reverse order as set
out for dismantling.
Wiring diagram
LH = Left handle
RH = Throttle
HC = Heater switch
TT = Triple contact
IM = Ignition module
SC = Short-circuit switch
Gen = Generator
Blu = blue
Bl = black
Re = red
Bl/Blu = black/blue
Use a universal tool when checking
wiring and heating elements. Set the
instrument to measure resistance to
check for open circuits.
13
2
Electrical system
14
Fuel system
3.
3
Contents
Air filter ___________________________________ 16
Tank venting _______________________________ 17
Fuel filter __________________________________ 17
Fuel pump _________________________________ 18
Carburettor ________________________________ 18
Assembly _________________________________ 24
Carburettor settings _________________________ 25
Throttle ___________________________________ 27
15
3
Fuel system
In addition to the fuel tank and carburettor, the fuel system
consists of the air filter, fuel filter and tank venting.
All these components interact so that the engine receives
the optimal mixture of fuel and air to make it as efficient as
possible. Very small deviations in the carburettor setting or
a blocked air filter have a large effect on the running and
efficiency of the engine.
Air filter
Remove the air filter holder.
The carburettor can come from several different
manufacturers on our models, but the function and
repair methods are essentially the same.
Air filter
Dismantle the cover (A) and remove the
air filter (B).
The nylon filter comes in two models.
The standard filter has a mesh size of
80µ. There is also a 44µ unit available.
There is also a flock filter, also as an
accessory.
Separate the filter halves and clean the
nylon filter in warm soapy water.
The R-variant has a foam rubber filter.
WARNING!
!
NOTE!
Do not blow the filter clean with compressed air. It can be damaged. Ensure
that the filter is dry before refitting it.
Remove the foam rubber filter and
clean it in warm soapy water.
Do not clean not the filter with petrol. Hazardous!
The air filter comes apart. Separate the
two halves with a screwdriver.
Clean the filter in warm soapy water. If
the filter fabric is damaged the entire
filter should be changed.
The R-variant has a foam rubber filter.
Remove the foam rubber filter and
clean it in warm soapy water.
16
Fuel system
Impregnate the filter with air filter oil. Impregnate the filter with air filter oil.
Tip!
Place the filter in a plastic bag and
pour about a tablespoon of air filter
oil no. 531 00 60-76 into the bag.
Massage the oil into the air filter.
531 00 60-76
3
Tank venting
Check that the tank venting valve works
correctly.
Replace the fuel cap if the valve is
faulty.
531 03 06-23
Tank venting
Tank venting takes place through the
fuel cap and needs to be functional for
the engine to work.
• Remove the fuel hose from the
carburettor and empty the fuel from
the tank.
• Connect the fuel hose to pressure
tester no. 531 03 06-23.
• Pump up a pressure and vacuum of
50 kPa (0.5 bar) in the tank.
• The pressure should sink to 20 kPa
or return to normal pressure within 45
seconds.
The fuel cap can be taken apart for
cleaning.
Use a screwdriver and prise off the
housing (A) that contains a rubber
diaphragm (B) and a filter (C).
Knock the housing against a tabletop
so that the cover (D) over the diaphragm falls off.
Blow the filter (C) clean, and the
sintered filter (E), with compressed air
and mount the fuel cap in the reverse
order to how it was disassembled.
Make sure that the flat surface on the
cover (D) is turned towards the diaphragm.
Fuel filter
The fuel filter can be removed through
the tank’s fill hole.
502 50 83-01
Fuel filter
The fuel hose in the tank contains a
fuel filter. It is accessible through the fill
hole. Pull out the filter with your fingers
or with help of tool 502 50 83-01.
NOTE!
The fuel filter can snag under the
shaft bushing in the tank. With the
aid of a long screwdriver, loosen
the filter. Do not pull on the hose,
since it can easily be pulled from
the filter.
17
3
Fuel system
Clean the filter externally if it is not too
dirty.
Replace the filter if required.
Fuel pump
The fuel pump facilitates cold starts.
The pump cannot be repaired and must
be replaced if it stops working.
Note how the fuel hoses are connected
to simplify assembly.
If the filter is not too dirty, its surface
can be cleaned with a brush.
Otherwise it must be replaced.
Check the fuel hose for cracks and
leaks.
Make sure that the filter’s connection
neck is inserted as far as possible into
the fuel hose and that the O-ring is
sufficiently tight so that the filter cannot
slide off the tube.
Fuel pump
The fuel pump has the task of facilitating the start of the engine when cold.
The pump fills the carburettor with fuel
before attempting to start the engine.
This also prevents vapour bubbles from
blocking the narrow fuel channels.
If the pump does not work it must be
replaced.
Note how the fuel hoses are connected
to simplify assembly.
Carburettor
Dismantling
Blow clean the carburettor compartment.
Loosen the bolts (A) and remove the
nuts (B).
Remove the fuel hose (C) and fold the
filter holder aside.
505 38 13-08 502 50 18-01
Move the fuel tank so far forward that
the fuel hoses (C) and (D) can be
removed.
Carburettor
Dismantling
1.Remove the carburettor cover and
blow the carburettor compartment
clean with compressed air.
2.Loosen the bolts (A).
3.Remove the nuts (B).
4.Remove the fuel hose (C) from the
carburettor and the filter holder.
5. Move the fuel tank so far forward
that the fuel hose (C) becomes
accessible.
Move the O-ring back and remove
the hose from the nipple.
Also remove the fuel hose (D) from
the nipple on the tank.
18
Fuel system
3
Remove the throttle cable and fuel hose
from the carburettor.
Remove the carburettor.
The carburettor is made by Zama.
Design, function and servicing correspond with the Walbro carburettor.
Default carburettor settings:
H = 1 revolution open
L = 1 revolution open
The carburettor needles are fitted with
movement limiters (caps).
Remove the throttle cable from the
carburettor’s lever arm using flat nose
pliers.
Pull off the fuel hose and remove the
carburettor.
Tip!
Open the fuel cap to avoid fuel spillage
caused by any excess pressure.
Attach the fuel hose to the return
nipple.
The carburettor is made by Zama.
It has the same design and function as
the Walbro carburettor, which means
that servicing is also carried out in the
same way.
The lever arm should lie flush with the
carburettor housing’s contact face.
Default carburettor settings:
H = 1 revolution open
L = 1 revolution open
The carburettor’s design
The carburettor can be divided into
three different functional units: the
metering unit, the blending unit, and the
pump unit.
The metering unit
The needles and the fuel control
functions are located here.
The blending unit
Fuel and air are mixed here.
The carburettor needles are fitted with
movement limiters (caps).
The carburettor’s design
The carburettor can be divided into
three different functional units: the
metering unit, the blending unit, and the
pump unit.
The metering unit
The needles (A) and the fuel control
functions are located here.
The needle valve (B) and control
diaphragm (C) are vital to the carburettor’s function.
The blending unit
In this section of the carburettor fuel
and air are mixed in the proper proportions.
The choke and throttle valves are
placed here.
In the middle of the venturi (narrowest
part of the throughput) the main jet (D)
is found.
19
3
Fuel system
The pump unit
Pumps fuel from the tank to the carburettor.
Dismantling the carburettor
Remove the control diaphragm and
check for damage.
Replace if required.
The pump unit
This is where the pump diaphragm (E)
that pumps fuel from the tank to the
carburettor’s measuring unit is found.
The diaphragm is affected by pressure
variations in the engine’s crankcase via
an impulse channel (F).
If the channel is blocked, by grease or a
wrongly facing gasket, for example, the
pump unit does not function and the
engine cannot be started.
Dismantling the carburettor
0Carefully remove the control diaphragm (A) and gasket (B).
Check the diaphragm for holes and
wear on the pin (C).
Replace the diaphragm if required.
20
Pressure test the metering unit.
531 03 06-23
Connect pressure tester 531 03 06-23
to the fuel hose nipple.
Lower the carburettor in a vessel with
petrol in order to discover any leaks
more easily.
Test the pressure at 50 kPa.
No leakage is permitted.
Fuel system
3
In the event of leakage – remove the
needle valve.
Check the needle valve and the lever
arm for damage or wear.
Replace damaged components with
new ones.
In the event of leakage – remove the
needle valve.
Loosen the bolt and remove the lever
arm, axle, needle valve and spring.
Check the needle valve for damage on
the tip and in the lever arm groove.
Check the lever arm for damage to the
groove for the needle valve and wear
on the mounting points towards the
control diaphragm.
Replace damaged components with
new ones.
Remove the pump diaphragm.
Check the diaphragm for damage.
Remove the fuel screen and clean it or
attach a new one.
Remove the bolt holding the cover over
the pump diaphragm.
Lift off the cover (A), the gasket (B) and
the diaphragm (C).
Check the diaphragm for damage to the
valve tongues. If the valve tongues are
bent, the pump will not function in a
satisfactory manner.
Hold it up to a light as well to discover
any holes in the material.
Carefully remove the fuel screen (D),
using a needle for example. Clean or
replace the fuel screen.
NOTE!
During assembly the pump
diaphragm should lie closest
to the carburettor housing.
21
3
Fuel system
Remove the movement limiters from the
jet needles using flat nose pliers.
Unscrew the jet needles.
Do not lose the small washers (A)!
Lift off the plastic and rubber guides.
NOTE!
Note how the jets are
positioned.
(For example, the H-needle is a
little shorter than the L-needle).
Dismantle the main jet (A) and the plug
(B).
Check valves and dampers for wear.
Replace if required.
Press out the main jet (A) with a
suitable punch.
Remove the plug (B).
Carefully drill a small hole (Ø 2 mm) in
the plug and pry it up with a pointed
object.
Remove the valves and dampers. If
these components are worn, idling is
disrupted.
Always replace the valves and dampers
at the same time.
22
Fuel system
3
Assembling the carburettor
Blow the carburettor housing clean.
Fit a new plug.
Fit a new main jet.
Assembling the carburettor
• Blow all channels in the carburettor
compartment clean
• Mount a new plug.
Use a suitable punch to get a
completely tight seal.
• Press in a new main jet.
• Mount the valves and dampers.
Tip!
Any numbers on the valves should be
able to be read from the outside.
Replace the fuel screen if it is damaged
or cannot be cleaned.
Place the pump diaphragm closest to
the carburettor housing. Then the
gasket and cover and the other components in reverse order of removal.
NOTE!
Check that the valves are turned
correctly and that they close
completely and tightly in the
closed position.
Use Loctite on the valve screws.
23
3
Fuel system
Attach the various parts of the measuring unit in the reverse order as set out
for dismantling.
Check that the carburettor is sealed.
No leakage is permitted at 50 kPa.
Attach the various parts of the measuring unit in the reverse order as set out
for dismantling.
The lever arm should lie flush with the
carburettor housing.
Too high setting = too much fuel.
Too low setting = too little fuel.
NOTE!
The H-needle is a little shorter
than the L-needle.
Connect pressure tester 531 03 06-23
to the fuel intake on the carburettor.
Pump up the pressure to 50 kPa.
Lower the carburettor in a vessel with
petrol in order to discover any leaks
more easily.
No leakage is permitted.
531 03 06-23
Attach the control diaphragm and
cover.
Assembly
Slide the carburettor into place and
connect the fuel hoses.
Make sure that they do not get pinched.
Connect the throttle cable to the
carburettor.
Place the gasket on the carburettor
housing and then the control diaphragm.
Check that the air hole in the cover is
open and screw the cover on.
Assembly
Slide the carburettor into place.
Connect the fuel hose (A) to the carburettor.
Connect the fuel hose (B) to the carburettor
and make sure that it is in the groove (C).
Place the filter holder in place and make
sure that the fuel hose (D) is under the
carburettor and is not pinched.
Connect the throttle cable (E) to the
carburettor.
Screw down the filter holder and attach
the air filter.
24
NOTE!
Check carefully that the fuel hoses
are not bent or pinched when the
fuel tank is pushed back into
place against the engine body.
Fuel system
Carburettor settings
WARNING!
!
When testing the engine in connection with carburettor
adjustment, the clutch and clutch cover must be mounted
together with the shaft and angle gear under all circumstances
Otherwise there is a risk of the clutch becoming loose resulting in
serious personal injury.
3
T
Function
The carburettor has the task of supplying a combustible fuel/air mixture to the
cylinder.
The amount
The mixture’s composition
“H” and “L” needles.
The needles must be correctly adjusted in order for the engine to give maximum
power at different speeds, run steadily while idling and to react quickly when
accelerating.
The setting of the carburettor can vary a little depending on the humidity, temperature and air pressure.
L = Low speed needle
H = High speed needle
T = Idle adjustment screw
• The fuel quantity in relation to the air flow permitted by the throttle opening is
adjusted by the L and H jets. Turning the needles clockwise gives a leaner fuel
mixture (less fuel) and turning them anticlockwise gives a richer fuel mixture (more
fuel).
• The T-screw regulates the position of the throttle while the engine is idling.
Turning the screw clockwise gives a higher idling speed while turning it anticlockwise gives a lower idling speed.
Basic setting
The carburettor is set to its basic setting when test run at the factory. The basic
setting is “richer” than the optimal setting (fast idle speed is 600–800 rpm under the
recommended max. speed) and should be kept during the engine’s first working
hours. Thereafter the carburettor should be fine tuned.
The default setting is:
H = 1 revolution open
L = 1 revolution open
of this mixture is controlled by the throttle.
of fuel and air is controlled by means of the adjustable
A leaner
mixture gives
higher
revs while
a richer
mixture gives
less
revs.
Fine adjustment
Fine adjustment of the carburettor should be carried out after the engine has been
“run-in”.
• The air filter should be clean and the cylinder cover fitted when all adjustments
are made.
First adjust the L-needle, then the H-needle and finally the idling speed’s Tscrew.
Idling speed = 2,800 rpm.
• Since the ignition system is limited in terms of rpm, the pre-programmed fast
idle speed (12,500 – 13,500 rpm) cannot be exceeded even if the H-needle is
screwed inwards. The risk in this case is still that the engine breaks down as a
result of a too lean fuel/air mix.
• At full throttle, the H-needle shall have a setting so that the engine is almost
splutters.
25
3
Fuel system
When checking the speed on a
trimmer no part of the cord
should be extended.
Use the 502 71 14-01 tachometer to check the speed.
502 71 14-01
501 60 02-03
• Start the engine and run warm for 10 minutes.
Low speed jet L
Find the highest idling speed by slowly turning the low speed
needle clockwise and anticlockwise. When the highest speed
has been found, turn the L-needle 1/4 turn anticlockwise.
High speed jet H
The high-speed H-needle affects the engine’s power and
speed. A too lean H-needle setting (H-needle screwed in too
far) gives too little fuel to the engine resulting in damage to
the engine.
Run the engine at full throttle for about 10 seconds. The Hneedle is set correctly when the engine “splatters” a little.
If the muffler smokes heavily, at the same time as the engine
“splatters” a great deal, the setting is too “rich”. Turn the Hneedle clockwise until you find the setting that sounds right.
• Carefully screw in (clockwise) the L- and H-jets until
they bottom. Now screw out
(anticlockwise) the needles
1 turn. The carburettor now
has the setting H = 1 and
L = 1.
Use special screwdriver 501
60 02-03.
NOTE!
A tachometer should always be used to find the optimal
setting.
The recommended max. speed must not be exceeded.
Idling speed T-screw
Let the engine idle for about 30 seconds or until the speed has
stabilised. Adjust the idling speed T-screw until the engine
idles without stopping.
• Turn the screw clockwise if the engine stops.
• Turn the screw anticlockwise to lower the speed.
Correctly adjusted carburettor
A correctly adjusted carburettor means that the engine
accelerates without hesitation and it “splatters” a little at full
throttle.
• A too lean adjusted L-needle can cause starting difficulties
and poor acceleration.
• A too lean adjusted H-needle results in lower power, poor
acceleration and/or damage to the engine.
• A too rich setting of the “L” and “H” needles give accelera-
tion problems or a too low working speed.
NOTE!
If the cutting equipment rotates while idling the Tscrew should be turned anticlockwise until it stops.
26
Carburettors in E-Tech and CARB-EPA designs (CARB II-EPA II only
applies to USA and Canada)
On these types of carburettor the H- and L-needles can be adjusted within extremely tight limits, to among other things, comply with the stringent demands with
regard to the hydrocarbon and nitrogen oxide content in the exhaust fumes.
The carburettor needles on these carburettors are fitted with plastic sleeves with
movement limiters, so-called caps.
To carry out adjustment when replacing needles or the entire carburettor the engine
must be under load. This is achieved by fitting a Trimmy Fix with the specified length
and diameter of trimmer cord. Consequently, the stated speed will be much lower
than with “normal” carburettor adjustment when the engine may run freely.
After replacing the needles or the entire carburettor on a CARB-EPA approved
engine, adjustment must be carried out according to the instructions below.
The combiguard or trim guard must be fitted when adjusting the H-needle.
Fuel system
3
Carburettor adjustment 345RX/FX
Adjusting the L-needle
1. Mount the Trimmy Fix (4 wires) and use 3.3 mm smooth
cord. The cord length should be 160 mm measured from the
end of the cord to the cord bushing on the trimmer head.
2. Run the engine warm for about 5 minutes.
3. Turn the L-needle so that the highest speed is attained.
4. If the speed exceeds 3,700 rpm, reduce it with the aid of the
idling speed’s T-screw (T) and a carry out a new adjustment
in accordance with point 3.
5. Then turn the L-needle anticlockwise so that the speed drops
by 300 rpm.
6. Then adjust the idling speed to 2,800 rpm by turning the Tscrew.
7. When mounting the plastic sleeve on the L-needle, the
needle is turned a quarter-turn anticlockwise once the
optimal setting has been made and the plastic sleeve is
mounted so that the needle cannot be turned anticlockwise.
Then turn the L-needle back a quarter-turn.
Carburettor adjustment 345RX/FX
Adjusting the H-needle
1. Mount the Trimmy Fix (4 wires) and use 3.3 mm smooth
cord. The cord length should be 160 mm measured from
the end of the cord to the cord bushing on the trimmer
head.
2. Run the engine warm for about 5 minutes.
3. Turn the H-needle so that the highest speed is attained.
4. Reduce the speed by 400 rpm by turning the H-needle
anticlockwise. Mount the plastic sleeve on the H-needle
so that it cannot be turned anticlockwise.
5. Then increase the speed by 200 rpm by turning the Hneedle clockwise.
NOTE!
If the cutting equipment rotates while idling the Tscrew should be turned anticlockwise until it stops
rotating.
531 00 48-63
531 03 03-98
Throttle
Disassemble the cable protector (B),
the cover (D) and the throttle from the
handle.
Remove the bolts and separate the two
halves of the throttle.
Carburettor needles with Zama “caps”.
Throttle
Remove the bolt (A) and cable protector (B).
Remove the two bolts (C) and the cover
(D).
Remove the bolt (E) that attaches the
throttle to the handle and remove the
throttle.
Remove the bolts and separate the two
halves of the throttle.
502 50 18-01
27
3
Fuel system
G
Check for wear on pins (A) and (B).
Replace the throttle control (C) and
lever arm (D) if necessary.
Check that the cables are properly
pressed into the cut-outs (E) and that
the throttle cable (F) is in the right
groove.
If necessary, attach it with silicon
adhesive in order to facilitate assembly.
Check that the protective bellows (G)
are whole and that they are correctly
mounted over the ball on the cable.
Remove the bolt (A) and remove the
throttle from the handle.
Remove bolts (B) and (C).
Separate the halves of the throttle.
Remove the bolt (A) that attaches the
throttle to the handle.
Be careful not to lose the nut.
Remove the throttle and remove bolts
(B) and (C).
Carefully separate the two halves of the
throttle.
28
Fuel system
3
Disassemble the throttle control (A), the
lock to prevent accidental throttle
operation (B), the start throttle lock (C)
and the throttle stop (D) in order to
check if replacement is necessary.
The stop switch can also be disassembled now, and replaced if necessary.
Use a screwdriver to press the stop
switch’s wing locks (E).
Tip!
Reassembly of the throttle easier if a
thin steel wire is wrapped around the
handle and bolt (F) in order to hold the
throttle cable and short-circuit cables in
place.
29
30
Centrifugal clutch
4.
4
Contents
Dismantling ________________________________ 30
Assembly _________________________________ 32
Clutch drum _______________________________ 32
31
4
Centrifugal clutch
The centrifugal clutch has the task of transferring the
power from the engine to the cutting equipment’s drive
axle. As the name implies, it works according to a centrifugal principle.
This means the clutch’s friction shoes are thrown outwards towards the clutch drum at a certain engine speed.
When the friction against the drum is sufficiently great it
drives the drive shaft at the same speed as the engine.
Dismantling
Dismantle the cable protector, loosen
bolts (A) and (B).
Some slipping occurs between the clutch and the
clutch drum when accelerating as well as in the
reversed situation when the cutting equipment jams.
Thereby preventing abnormal load changes on the
crankshaft.
The engagement speed has been carefully tested so
that the engine can idle without the cutting equipment’s drive shaft rotating.
Dismantling
The clutch is located between the fuel
tank and the engine.
In order to be accessible, the tank and
handle holder must be moved forward
on the shaft.
1. Dismantle the cable protector.
2. Loosen bolts (A) and (B).
Move the fuel tank so far forward that
the fuel hoses (C) and (D) can be
removed.
Remove the 4 bolts holding the clutch
cover.
Dismantle the vibration dampers for
better access.
3. Move the fuel tank so far forward
that the fuel hose (C) becomes
accessible.
Move the O-ring back and remove
the hose from the nipple.
Also remove the fuel hose (D) from
the nipple on the tank.
Move the fuel tank further forward and
remove the 4 bolts holding the clutch
cover to the engine.
Remove the vibration dampers from
their plugs in order to facilitate dismantling.
32
502 21 58-01
Centrifugal clutch
4
Dismantle the clutch from the crankshaft.
502 54 15-01
Remove the 3 bolts and separate the
clutch.
Replace the spark plug with piston stop
no. 502 54 15-01.
Move the engine body to the side so
that the clutch becomes accessible.
Unscrew the clutch from the crankshaft.
Fix the clutch in a vice and remove the
3 bolts.
Lift off the front cover plate and the
clutch shoes.
NOTE!
Do not lose the sleeve bearings
found in the clutch shoes.
Twist apart the clutch. Twist apart the clutch.
Clean and inspect the different parts
with regard to wear or other damage.
Clean and inspect the different parts
with regard to wear or other damage.
Wear on the clutch shoes must not be
greater than shown in the illustration.
Check the play in the sleeve bearings in
the clutch shoes and the wear on the
springs by the fastening hooks.
33
4
Centrifugal clutch
Assembly
Temporarily place the clutch shoes on
the driving disc and loosely tighten the
bolts.
Pry out the shoes and hook one spring
to each shoe from underneath.
Get in the clutch shoes as far as
possible and hook the springs to the
adjacent clutch shoe.
Remove the bolts and mount the cover
plate.
Fit the clutch to the crankshaft and the
remaining parts in the reverse order as
set out for dismantling.
Assembly
Temporarily place the clutch shoes on
the driving disc and loosely tighten the
bolts.
NOTE!
The bevelled edge of the shoes
should be facing outwards
towards the cover plate.
Pry out the shoes and hook one spring
to each shoe from underneath.
Fold in the clutch shoes as far as
possible and hook the springs to the
adjacent clutch shoe.
Use a small screwdriver or flat-nosed
pliers.
NOTE!
Make sure that the spring eye is
pressed into the correct position.
Clutch drum
Dismantle the clutch housing and the
clutch drum and drive axle from the
shaft.
Unscrew the clutch drum from the drive
axle.
Remove the bolts and put the cover
plate in place.
Tighten the bolts, fit the clutch to the
crankshaft and the remaining parts in the
reverse order as set out for dismantling.
Clutch drum
Separate the engine body and shaft as
described previously.
Loosen the bolts holding the clutch
housing against the shaft.
Remove the clutch housing and drive
axle from the shaft.
Unscrew the clutch drum from the drive
axle.
NOTE!
Avoid fixing the drive axle in a
vice. Marks can form on the axle
even if protective jaws are used.
This in turn leads to damage on
the plastic insert in the shaft.
34
502 52 16-02
Use tools 502 52 16-02 and 502 11 46-03.
Check the clutch drum for wear. The
internal diameter must not exceed
70.0 mm.
502 11 46-03
Centrifugal clutch
4
Change the bearings in the clutch
housing if necessary.
505 38 17-09
Change the bearings in the clutch
housing if necessary.
Remove the circlip and push out the
bearings with a suitable punch and
hammer.
Dismantling is easier if the clutch
housing is heated to about 110°C.
Assemble in the reverse order as set
out for dismantling.
35
36
Angle gear
5.
5
Contents
Dismantling ________________________________ 36
Assembly _________________________________ 37
Shaft _____________________________________ 38
37
5
Angle gear
The angle gear has two purposes:
The first is to gear down the engine’s high speed to
better suit the lower speed a saw blade or trimmer
requires to work efficiently.
Dismantling
Remove the cutting equipment and
guard.
Then loosen the bolts holding the angle
gear against the shaft.
Remove the angle gear from the shaft.
Second, the angle gear contributes to the saw operator’s working stance so that it is comfortable and at the
same time efficient. The power from the engine, via the
drive axle, shall in other words be angled so that the
cutting equipment works parallel to the ground.
Dismantling
First remove the cutting equipment
(saw blade, trimmer etc.) and guard.
Then loosen the bolts holding the
angle gear against the shaft.
Remove the angle gear from the shaft.
Use a screwdriver if necessary to
separate the mechanical joint.
Remove the circlip and washer on the
output axle.
Remove the large circlip from the input
axle.
Remove the circlip on the output axle
using circlip pliers.
Lift off the washer from the sealing ring.
Remove the large circlip from the input
axle.
NOTE!
Let the small circlip around the
axle remain.
38
Angle gear
5
Remove the lubricant top-up plug.
Warm the gearbox and knock it against
a wooden block so that the input axle
falls out.
Remove the output axle. Then remove the output axle and
Remove the lubricant top-up plug and
warm the entire gearbox using a hot air
gun to about 150°C.
Knock the gearbox against a wooden
block so that the input axle and bearing
fall out.
NOTE!
The input axle with pinion must
be dismantled first.
bearings, while the gearbox is still
warm.
Use puller no. 502 50 65-01.
502 50 65-01
503 97 64-01
Assembly
Replace damaged parts.
Assemble the angle gear in the reverse
order as set out for dismantling.
Fit the bearings on their respective
axles. It is easier if the bearings are
heated to approx. 100°C.
NOTE!
Do not forget the circlip holding
the bearing on the input axle.
Make sure the bearings bottom in
their seats.
Heat the gearbox to approx. 150°C and
first lift the output axle in position and
then the input axle. Make sure the
bearings bottom in their seats.
Mount the circlips and make sure they
lie correctly in their grooves.
Rotate the axles and check that they
rotate easily without a tendency for the
cogwheels to seize.
Fill the gearbox with special grease no.
503 97 64-01. Wipe any excess grease
from the joint between the shaft and the
angle gear before the gear is fitted to
prevent it from turning around the shaft.
39
5
Angle gear
Shaft
The shaft contains a drive axle guide
that is easily replaced. It can be
dismantled once the plastic sleeve (B)
has been removed.
Centre the axle control in the shaft
when a new one is fitted.
Fit a new O-ring to ensure a good seal.
503 80 17-01
Shaft
The shaft contains a long plastic guide
to prevent vibrations in the drive axle.
The guide (A) is easily removed for
replacement.
Bend away the plastic sleeve (B) and
the O-ring (C) using a knife and pull the
drive axle guide out from the shaft.
When replacing the axle guide, the
replacement must be inserted into the
shaft so that the distance is the same to
the two ends of the shaft.
When fitting, a new O-ring must be
used. To avoid damage from the sharp
edges of the slits in the gearbox, the
following assembly procedure is
recommended:
1. Place the plastic sleeve (B) in
position in the gearbox.
2. Slide the O-ring (C) onto the plastic
sleeve.
3. Slide the shaft and guide (A) into
position.
Lubricate the drive axle with grease no.
503 80 17-01 when assembling.
40
Cylinder and piston
6.
6
Contents
Dismantling ________________________________ 42
Decompression valve ________________________ 43
Inlet manifold ______________________________ 44
Cleaning, inspection _________________________ 44
Assembly _________________________________ 44
Analysis and actions _________________________ 45
Service tips ________________________________ 49
Wear tolerances ____________________________ 50
41
6
Cylinder and piston
The cylinder and the piston are two of the components exposed to most strain in the engine. They must
withstand, for example, high speeds, large temperature swings and high pressure. Moreover, they must
be resistant to wear. Despite these tough working
conditions, major piston and cylinder failure is relatively uncommon. The reasons for this include new
coatings in the cylinder bore, new types of oil and
grease and refined manufacturing techniques.
Dismantling
Dismantle the following components to make the cylinder accessible:
Starter, cylinder cover, muffler guard, muffler and spark plug.
NOTE!
The throttle need not be removed to dismantle the cylinder and piston.
A
Loosen the clamp (A) and unscrew the bolt a good distance (to facilitate the coming
assembly) so that the clamp can be turned around the inlet manifold without
affecting the cylinder.
Then loosen the 4 bolts holding the cylinder.
Carefully lift out the cylinder by twisting is backwards and forwards until it loosens
from the inlet manifold. Make sure that no dirt enters the crankcase.
Use a rag to cover the crankcase opening under the piston.
When servicing these components, cleanliness is of
the utmost importance. It is therefore recommended
that the cylinder and the area around it be thoroughly
cleaned before being dismantled from the crankcase.
502 50 18-01
Remove the circlips from the gudgeon
pin.
Using long-nose pliers remove the
gudgeon pin circlips.
Keep your thumb over the circlip to
prevent it from flying out.
42
Cylinder and piston
6
Dismantle the piston.
502 52 42-01
Decompression valve
Dismantle the decompression valve.
Push the gudgeon pin from the piston
using punch 502 52 42-01.
If the pin is too tight, carefully warm the
piston.
Decompression valve
Remove the bolt (A) and the hose (B)
that connect the decompression valve
to the nipple on the cylinder.
Unscrew the valve from the cylinder.
Check that the non-return valve (A) is
tight under a vacuum of – 50 kPa.
Otherwise replace the valve.
NOTE!
Turn the valve the right way when
fitting.
531 03 06-23
Clean the decompression valve and
check that the valve head is not damaged (burnt) and that the valve operates easily.
If necessary, grind the valve with finegrained valve grinding compound.
Inside the rubber sleeve on the nipple
in the cylinder is a non-return valve (A).
Check with pressure gauge 531 03 06-23.
Pump up a vacuum of – 50 kPa. The
valve must be fully tight. Otherwise
replace the valve.
NOTE!
When the valve is fitted the small
hole must face outwards.
Clean the decompression valve with
white spirit or thinner and blow dry with
compressed air.
Check that the valve moves easily in
the guide and that the valve head is not
damaged (burnt).
If necessary, grind the valve into the
seat using fine-grained valve grinding
compound.
Tip!
Use washer no. 502 54 11-01 as a
friction lining against the valve head
when grinding.
Fit the decompression valve in the cylinder.
43
6
Cylinder and piston
Inlet manifold
Remove the air filter and carburettor.
Remove the inlet manifold (A) from the
partition (B). Check that it does not
exhibit cracks or other damage that can
cause leaks between the carburettor
and cylinder. If necessary, fit a new inlet
manifold in the reverse order as set out
for dismantling.
NOTE!
Exercise caution if the inlet
manifold is fitted using a
screwdriver so as not to make any
holes in the rubber wall.
Cleaning, inspection
After dismantling, clean the individual components:
1. Scrape carbon deposits from the top of the piston.
2. Scrape carbon deposits from the cylinder’s combustion chamber.
3. Scrape carbon deposits from the cylinder’s exhaust por t.
NOTE!
Scrape carefully with not too sharp a tool so as not to damage the soft
aluminium parts.
4. Wash all the components.
5. Inspect the different components for damage and wear.
Check the piston and cylinder for seizure damage and wear.
Also see the “Analysis and actions” section.
Check the piston ring for wear and damage.
Also see the “Analysis and actions” section.
Check the gudgeon pin.
– If it has blued, it must be replaced.
– If the piston moves too easily both the piston and the gudgeon pin must be replaced.
Check the needle bearing. If it is discoloured or damaged, it must be replaced.
Check the circlips. If they exhibit cracks or are discoloured (caused by overheating),
they must be replaced.
Assembly
Lubricate the gudgeon pin’s needle
bearing with a few drops of engine oil
and fit the piston.
Assembly
Lubricate the gudgeon pin’s needle
bearing with a few drops of engine oil.
Direct the arrow on the top of the piston
towards the exhaust port.
Press in the gudgeon pin and fit the
circlips.
44
NOTE!
Place a rag in the crankcase opening to prevent the circlip from falling
into the crankcase in case it should fly out.
Check that the circlips are correctly fitted into the grooves by turning the
clips with long-nosed pliers.
Cylinder and piston
6
Use a new gasket and fit the cylinder.
Make sure that the inlet manifold is
correctly connected to the sleeve
coupling on the cylinder and that the
impulse nipple sits right.
502 50 70-01
Screw the cylinder into place and
tighten the clamp around the inlet
manifold.
Assemble the other parts.
Place a new cylinder pedestal gasket
on the cylinder.
Lubricate the piston and the inlet
manifold on the cylinder with a few
drops of engine oil and fit the cylinder
using the smallest piston ring compressor in assembly kit 502 50 70-01.
Make sure that the inlet manifold is
correctly connected to the sleeve
coupling on the cylinder and that the
impulse nipple sits right.
Screw the cylinder into place.
Tighten the clamp around the inlet
manifold.
Assemble the carburettor and the other
parts in the reverse order as set out for
dismantling.
Small to medium size scores primarily in
the middle of the exhaust port.
Analysis and actions
Experience tells us that piston or cylinder failure due to manufacturing errors are
extremely rare.
The reason is usually due to other factors, which is evident from the following.
Note the reasons for the breakdown, repair the damage and take the actions
required to prevent the same thing happening again.
Insufficient lubrication
The piston has small to medium size score marks usually in front of the exhaust
port. In extreme cases heat development can be so great that material from the
piston smears along the piston skirt and even in the cylinder bore.
Generally the piston ring is undamaged and moves freely in the ring groove
There can also be scores on the inlet side of the piston.
Cause:
• Incorrect carburettor setting.
Recommended max. speed exceeded.
• Incorrect oil mixture in the fuel.
• Too low octane fuel.
Action:
Check and change the carburettor
setting.
Change the fuel.
Change to a higher octane petrol.
45
6
Cylinder and piston
The piston ring starts to stick or is completely stuck in its groove and has therefore
not been able to seal against the cylinder wall, which has resulted in further,
intensive temperature increases in the piston
Seizure scores along the entire piston skirt on the inlet and exhaust sides.
Medium to deep scores along the entire
piston skirt on the exhaust side.
Cause:
• Incorrect oil mixture in the fuel.
• Too low octane fuel.
• Air leaks.
Cracked fuel hose.
Leaking inlet gaskets.
Cracked distance piece or inlet
manifold.
• Air leakage in engine body.
Leaking crankshaft seals.
Leaking cylinder and crankcase
gaskets.
• Poor maintenance.
Dirty cooling fins on the cylinder.
Blocked air intake on the starter.
Blocked spark arrestor mesh in
the muffler.
For the best results we recommend Husqvarna two-stroke oil or ready-mixed fuel
that is specially developed for air-cooled two-stroke engines.
Mixing ratio: 1:50 (2%).
If Husqvarna two-stroke oil is not available another good quality two-stroke oil can
be used.
Mixing ratio: 1:33 (3%) or 1:25 (4%).
Action:
Change to a fuel with the correct oil
mixture.
Change to a higher octane petrol.
Replace damaged parts.
Replace leaking gaskets and shaft
seals.
Clean the cooling fins and air intake.
Clean or replace the spark arrestor
mesh.
Medium to deep scores on the exhaust side.
The piston ring is stuck in the groove.
Black discoloration under the piston ring
due to blow-by.
Piston scoring caused by heavy carbon deposits
Too heavy carbon depositing can cause damage similar to that caused by insufficient lubrication. However, the piston skirt has a darker colour caused by the hot
combustion gases that are blown past the piston.
This type of piston damage starts at the exhaust port where carbon deposits can
become loose and get trapped between the piston and the cylinder wall.
Typical for this type of piston damage is brown or black discoloration of the piston
skirt.
Cause:
• Wrong type of two-stroke oil or
petrol.
• Incorrect oil mixture in the petrol.
• Incorrect carburettor setting.
Action:
Change the fuel.
Change to a fuel with the correct oil
mixture.
Correct the carburettor setting
46
Exhaust side damaged by a broken piston
ring. The piston ring parts damage the top
section and cause score marks.
Cylinder and piston
Piston damage caused by a too high engine speed.
Typical damage associated with a too high engine speed includes broken piston
rings, broken circlip on the gudgeon pin, faulty bearings or that the guide pin for the
piston ring has become loose.
Piston ring breakage
A too “lean” carburettor setting results in a too high speed and a high piston
temperature. If the piston temperature rises above the normal working temperature
the piston ring can seize in its groove, consequently it will not sit deep enough in its
groove. The edges of the piston ring can then hit the top edge of the exhaust port
and be smashed and also cause piston damage.
A too high engine speed can also cause rapid wear to the piston ring and play in
the piston ring groove primarily in front of the exhaust port. The ring is weakened by
the wear and can be caught in the port causing serious piston damage.
6
The guide pin for the piston ring has been
pushed up through the top of piston.
Piston ring guide pin
vibrated loose
A too high engine speed can cause the
ends of the piston ring to hammer against
the guide pin when the piston ring moves
in its groove. The intensive hammering
can drive out the pin through the top of
the piston causing serious damage also
to the cylinder.
Deep, irregular grooves caused by a loose
circlip. Shown here on the piston’s inlet
side.
Damage caused by
gudgeon pin circlips
A too high engine speed can cause the
gudgeon pin circlips to vibrate. The
circlips are drawn out of their grooves due
to the vibrations, which in turn reduces
the circlips’ tensioning power. The rings
can then become loose and damage the
piston.
Irregular grooves on the piston’s inlet side
caused by a broken roller retainer.
Bearing failure
Failure of the crankshaft bearing or on the
connecting rod bearing is usually caused
by a too high engine speed, resulting in
the bearing being overloaded or overheating. This in turn can cause the bearing
rollers or ball to glide instead of rotate,
which can cause the roller or ball retainer
to break.
The broken debris can be trapped between the piston and cylinder wall,
damaging the piston skirt.
Debris can also pass up through the
cylinder’s transfer channels and cause
damage to the top and sides of the piston
as well as to the cylinder’s combustion
chamber.
47
6
Small score marks and a matt, grey surface
on the piston’s inlet side caused by fine
dust particles.
Cylinder and piston
Foreign objects
Everything other than clean air and pure fuel that enters the engine’s inlet port
causes some type of abnormal wear or damage to the cylinder and piston.
This type of increased wear shows on the piston’s inlet side starting at the lower
edge of the piston skirt.
The damage is caused by badly filtered air that passes through the carburettor and
into the engine.
Inlet side.
Particles of dust and dirt from carbon-like
deposits on the top of the piston and in the
piston ring groove. The piston ring sits
firmly in the groove. Piston material has
been worn away.
The lower part of the piston skirt is thinner
on the inlet side than on the exhaust side.
Cause:
• Faulty air filter. Small dust particles
pass through the filter.
• The filter is worn out due to too
much cleaning, whereby small holes
have appeared in the material.
• Unsuitable filter maintenance, such
as wrong method or wrong cleaning
agent. Flock material becomes
loose and holes appear.
• Air filter incorrectly fitted.
• Air filter damaged or missing.
Action:
Fit a finer grade filter.
Check the filter carefully for holes and
damage after cleaning. Replace the
filter if necessary.
Clean more carefully and use the right
cleaning agent (such as tepid soapy
water).
Change the filter.
Fit the filter correctly.
Fit a new air filter.
The piston scored and worn from the piston
ring down on the inlet side.
48
Larger, softer particles that penetrate into the engine cause damage to the piston
skirt under the piston ring as the illustration shows.
Cause:
• Air filter incorrectly fitted.
• Air filter damaged or missing.
Action:
Fit the air filter correctly.
Fit a new air filter.
Cylinder and piston
Larger, harder particles that enter the engine cause serious damage to the underside of the piston skirt.
6
Cause:
• Air filter damaged or missing.
• Parts from the carburettor or intake
system have come loose and
entered the engine.
Extensive damage to the lower part of the
piston’s inlet side.
Service tips
Defect:
Broken cooling fins, damaged threads or sheared bolts by
the exhaust port.
Seizure marks in the cylinder bore (especially by the
exhaust port).
Surface coating in the cylinder bore worn out (primarily at
the top of the cylinder).
The piston shows signs of seizure score marks.
Piston ring burnt in its groove.
Action:
Fit a new air filter.
Regular service and inspection.
Action:
In severe cases – replace the cylinder.
Repair the threads using Heli-Coil.
Polish the damaged area using a fine grade emery cloth
so that the coating of aluminium disappears.
With deep seizure score marks the piston and cylinder
should be replaced.
Replace the cylinder and piston.
Carefully polish the damaged area using a fine file of fine
grade emery cloth. Before the piston is refitted the cylinder
should be polished as above. With deep score marks the
piston and cylinder should be replaced.
Carefully loosen the piston rings and clean the groove well
before refitting. Carbon deposits in the groove impair the
important heat transfer between the piston and cylinder.
Bolts much too tight in the aluminium material.
NOTE!
Be careful with the lower edge of the piston ring
groove. If this is damaged, or if carbon deposits
remain, the compression pressure can leak through.
Check the wear on the piston ring by placing it in the lower
part of the cylinder.
Position a suitable punch on the bolt head and give a few
sharp knocks with a hammer. If the bolt still does not loosen,
repeat the procedure.
49
6
Wear tolerances
Cylinder and piston
Piston ring playPiston ring groovePiston ring gapCylinder bore
When the surface coating is
worn and aluminium appears.
Max. 1.0 mm with the piston
ring inserted in the lower part
of the cylinder.
Max. 1.6 mm. Clean the groove
before checking the measurement.
Max. 0.15 mm. Clean the groove
before checking the measurement.
50
Crankshaft and crankcase
7.
7
Contents
Dismantling ________________________________ 52
Inspecting the crankshaft _____________________ 54
Assembly _________________________________ 55
Leakage testing the crankcase_________________ 56
51
7
Crankshaft and crankcase
The task of the crankshaft is to transform the reciprocating
motion of the piston to rotation. This requires a stable
design withstanding immense pressure and rotational and
bending strain, as well as high rotational speed. In addition
the connecting rod is exposed to large acceleration and
retardation forces as it moves between the top and bottom
dead centres. This puts special demands on the bearings
that must withstand quick changes in load. Moreover, the
bearing’s roller retainer must also cope with high temperatures and friction. It is therefore extremely important when
servicing to check the roller retainer for cracks, wear and
discolouration caused by overheating.
Dismantling
Dismantle all components so that only
the crankcase and crankshaft remain.
Dismantle the guard under the crankcase.
The crankshaft is journalled in the crankcase on
heavy-duty ball bearings. In addition to the journalling
point for the crankshaft, the crankcase acts as a
scavenging pump for the fuel/air mixture when this is
“sucked” from the carburettor and is forced into the
cylinder’s combustion chamber. The crankcase must
be perfectly sealed so as not to affect this pump
function. There cannot be any leakage from the crankshaft, between the crankcase halves or between the
crankcase and the cylinder.
Always replace the sealing rings and gaskets when
servicing the crankcase.
Dismantling
Dismantle all components so that only
the crankcase and crankshaft remain.
See the respective sections for detailed
information if necessary.
Remove the 4 bolts and lift off the
guard from under the crankcase.
Bend away the heat guard (A) and
cable guide (B).
Remove the 4 bolts holding the crankcase halves together.
Bend away the heat guard (A) with your
fingers and carefully push the cable
guide (B) aside with a screwdriver.
Remove the 4 bolts holding the crankcase halves together.
52
502 50 18-01
Crankshaft and crankcase
Separate the crankcase halves. Fit tool 502 52 39-01 to the clutch side
of the crankcase as illustrated.
Separate the crankcase halves.
502 52 39-01
Fit tool 502 52 39-01 as illustrated.
7
Push out the crankshaft from the
crankcase half.
Remove the bearing and sealing rings
from the crankcase halves.
Push out the crankshaft from the
crankcase half.
Heat the crankcase halves to approx.
150°C using a hot air gun.
Knock the halves against a wooden
block so that the bearings fall out of
their seats.
Remove the gaskets with a suitable
punch.
505 38 17-09
53
7
Crankshaft and crankcase
Inspecting the
crankshaft
Inspect the large end of the connecting
rod.
Inspect the small end of the connecting
rod.
Inspecting the
crankshaft
The crankshaft cannot be reconditioned
but must be replaced if it is worn or
damaged.
Inspect the large end of the connecting
rod. If seizure marks, discolouration on
the sides or damaged needle holders
are found the crankshaft must be
replaced.
Inspect the small end of the connecting
rod.
If seizure marks or discolouration are
found in the bearing track the crankshaft must be replaced.
Check the crank bearing. Check the crank bearing. The connect-
ing rod shall not have any radial play
(up and down).
It should, however, have axial play, in
order to ensure good lubrication of the
crank bearing among other things.
Inspect the crankshaft bearing and
sealing rings.
Check for wear in the crankshaft
bearing and sealing rings.
Clean the bearings and rotate the outer
ring. If movement is “jerky” the bearing
track is probably damaged. If so,
replace the bearing.
Also check that the gap is not too great.
Inspect the sealing rings. The seal edge
shall be sharp or slightly ground.
54
Crankshaft and crankcase
7
Check that the there is no play in the
fill-out plates around the crank disks
(applies to models FX/FXT, RX).
Assembly
Mount the bearings in the crankcase
halves.
Check that the there is no play in the
fill-out plates around the crank disks
(applies to models FX/FXT, RX).
Assembly
Heat the crankcase halves to approx.
150°C using a hot air gun and position
the bearings.
Make sure they go right down into the
bearing seats.
First fit the crankshaft in the clutch-side
crankcase half.
502 50 30-19
Fit a new gasket to the clutch-side
crankcase half.
Pull the other crankcase half into
position and tighten the 4 crankcase
bolts.
Lubricate the big-end bearing with a
few drops of engine oil and position the
crankshaft in the clutch-side crankcase
half.
Pull the crankshaft into place with tool
no. 502 50 30-19.
Make sure that the connecting rod is
not squeezed against the crankcase!
Fit a new gasket to the clutch-side
crankcase half.
Place the other crankcase half over the
crankshaft and place the 4 crankcase
bolts so that they guide the gasket.
Pull the crankcase half into place with
tool no. 502 50 30-19.
Tighten the crankcase bolts.
Check that the crankshaft can rotate
easily. If not, hit the axle spindles
sharply a few times with a rubber
hammer so that the tension in the
crankshaft disappears.
502 50 30-19
55
7
Crankshaft and crankcase
Fit the sealing rings. Lubricate the axle spindles with engine
oil and press the sealing rings until
level with the crankcase using a
suitable punch or tool 502 50 30-19.
The metal covers of the sealing rings
should face outwards!
505 38 17-09
Assemble the remaining parts in the following order:
1. Cable guide and heat guard on the carburettor side of the crankcase.
2. Protective grating on the underside of the crankcase.
3. Piston and cylinder.
4. Partition on the carburettor side with attached inlet manifold.
NOTE!
If the inlet manifold has been removed, no sharp implements may be used
to replace it as there is a risk that holes will be made in the inlet manifold.
This would result in poor idling.
5. Generator. Make sure that the cable is pressed into the groove in the crankcase.
6. Flywheel.
7. Ignition module.
8. Muffler and heat shield.
9. Carburettor with fitted air filter holder and bushings for fuel hoses.
10. Clutch.
11. Shaft.
Leakage testing the
crankcase
Fit the two sealing plates (A) and the
pressure test nipple (B).
Leakage testing the
crankcase
Remove the throttle cable and air filter
holder from the carburettor. Fit a sealing
plate (A) 502 54 11-02 between the
carburettor and the distance piece and
a plate between the cylinder and the
heat guard plate by the muffler.
56
502 54 11-02 503 84 40-01
NOTE!
Press down the sealing plates as
far as possible between the bolts
to ensure a proper seal.
Fit the pressure test nipple (B)
503 84 40-01 in the spark plug hole.
Crankshaft and crankcase
7
Fuel consisting of
Hydrocarbons (petrol)
Two-stroke oil (2%)
Air consisting of:
21% oxygen
78% nitrogen
1% other
Fuel/air mixture consisting
of:
92% air
8% petrol
Fit plug 503 55 22-01 instead of the
decompression valve.
Connect meter 531 03 06-23 and check
for leakage.
531 03 06-23 503 55 22-01
Exhaust gases
consisting of
Hydrocarbon (HC)
Nitrous oxide (NOx)
Carbon monoxide (CO)
Carbon dioxide (CO2)
Particles (PM)
Fit plug 503 55 22-01 instead of the
decompression valve.
Connect meter 531 03 06-23 to the
nipple and pump up a pressure of 50
kPa (0.5 kp/cm
2
) in the crankcase.
Max. permitted leakage:
20 kPa (0.2 kp/cm2) per 30 seconds.
Connect meter 531 03 06-23 to the
nipple and lower the pressure in the
crankcase to 50 kPa (0.5 kp/cm
2
).
Max. permitted leakage:
20 kPa (0.2 kp/cm2) per 30 seconds.
Any leakage can be difficult to localise
if the crankcase is depressurised.
When leakage has been established
with a vacuum, you can apply a slight
overpressure (0.1–0.3 kp/cm
2
) and at
the same time apply a layer of thin oil to
the joints and the sealing ring contact
surfaces on the crankcase to make leak
detection easier. Bubbles clearly mark
the position of the leakage.
Husqvarna E-Tech
In 1996 Husqvarna presented a new,
improved two-stroke engine as a part
of the company’s efforts to produce
engines that emit smaller amounts of
hazardous substances.
The new engine was given the designation E-Tech and was first used in a
new brush cutter model.
More stringent environment regulations
in the USA, which primarily involve a
lowering of the hydrocarbons, nitrous
oxides and carbon monoxide content,
brought about the new engine design.
Environment degradation is reduced
through decreasing the amount of
unburned gases (flushing losses) in the
exhaust fumes.
Comparisons between an E-Tech
engine and an older engine design
show that the CO content has been
halved and the hydrocarbons and
nitrous oxide contents have been
reduced by close to 70%. In addition a
powerful increase in output is gained.
Adjustable fuel jets with
movement limiters
What makes the E-Tech engine design
unique is not a specific design solution
but rather several solutions interacting
to reduce flushing losses in the engine.
The carburettor’s job is to mix the air
and fuel in the right proportions to give
a combustible mixture, irrespective of
the speed and workload. The carburettor’s adjustable needles have been
fitted with movement limiters to prevent
the engine from being run with a too
“rich” fuel/air mixture. (Also see the
“Fuel system” chapter).
57
58
Loading...