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, trichlo- roethylene and other highly volatile liquids.

The engine exhaust is poisonous. Test run the engine only if ventilation is good. Preferably outside.

!WARNING!

Risk of personal injury if the instructions are not followed.

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.

NOTE!

Material damage may occur if the instructions are not followed.

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.

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.

Loosen the spring tension.

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.

Remove the bolt in the centre of the starter pulley. Lift the starter pulley carefully from the starter cover.

Assembly

Clean requisite parts and assemble in the reverse order as set out for disman- tling.

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.

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!

Anchor the cord in the starter handle.

Thread the cord through the starter handle and anchor it with a knot.

Fold down the free end and pull the knot well into the handle.

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.

Check if a spark occurs when attempt- ing to start.

Test with test spark plug no. 502 71 13- 01 if no spark is seen.

502 71 13-01

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.

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.

If no spark occurs, disconnect the stop switch.

Replace the switch if necessary

The stop switch can be easily detached with a screwdriver.

Still no spark?

Check the ignition cable???s connection to the spark plug cover.

Still no spark?

Check other cables and connections.

If no spark occurs even now, remove the short-circuit cable from the connec- tion point in the carburettor compart- ment.

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 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 connec- tion 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.

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.

Remove the flywheel.

502 51 94-01

Remove the ignition module and the generator.

502 50 18-01

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 from the crank- shaft 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.

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

502 51 34-02

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.

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

Use a universal tool when checking wiring and heating elements. Set the instrument to measure resistance to check for open circuits.

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.

The carburettor can come from several different manufacturers on our models, but the function and repair methods are essentially the same.

Remove the foam rubber filter and clean it in warm soapy water.

Remove the foam rubber filter and clean it in warm soapy water.

Impregnate the filter with air filter oil.

531 00 60-76

Tank venting

Check that the tank venting valve works correctly.

Replace the fuel cap if the valve is faulty.

531 03 06-23

Fuel filter

The fuel filter can be removed through the tank???s fill hole.

502 50 83-01

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.

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 dia- phragm 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 dia- phragm.

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.

Remove the throttle cable and fuel hose from the carburettor.

Remove the carburettor.

The carburettor is made by Zama.

Design, function and servicing corre- spond with the Walbro carburettor.

Default carburettor settings:

H = 1 revolution open

L = 1 revolution open

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 and the fuel control functions are located here.

The blending unit

Fuel and air are mixed here.

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 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 carburet- tor???s function.

The blending unit

In this section of the carburettor fuel and air are mixed in the proper propor- tions.

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.

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.

Remove the pump diaphragm. Check the diaphragm for damage.

Remove the fuel screen and clean it or attach a new one.

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 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.

Check valves and dampers for wear. Replace if required.

Remove the valves and dampers. If these components are worn, idling is disrupted.

Always replace the valves and dampers at the same time.

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 compo- nents 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.

T

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.

Function

The carburettor has the task of supplying a combustible fuel/air mixture to the cylinder.

The amount of this mixture is controlled by the throttle.

The mixture???s composition of fuel and air is controlled by means of the adjustable ???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, tempera- ture 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). A leaner mixture gives higher revs while a richer mixture gives less revs.

???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 anti- clockwise 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

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 T- screw.

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

Dismantling

Dismantle the cable protector, 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.

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).

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 disman- tling.

Dismantle the clutch from the crank- shaft.

502 54 15-01

Remove the 3 bolts and separate the clutch.

Twist apart the clutch.

Clean and inspect the different parts with regard to wear or other damage.

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.

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.

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.

Clutch drum

Dismantle the clutch housing and the clutch drum and drive axle from the shaft.

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.

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.

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.

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.

Change the bearings in the clutch housing if necessary.

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.

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.

Second, the angle gear contributes to the saw opera- tor???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

Remove the cutting equipment and guard.

Then loosen the bolts holding the angle gear against the shaft.

Remove the angle gear from the shaft.

Remove the circlip and washer on the output axle.

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 on the output axle using circlip pliers.

Lift off the washer from the sealing ring.

Remove the large circlip from the input axle.

Remove the large circlip from the input axle.

NOTE!

Let the small circlip around the axle remain.

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.

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.

Then remove the output axle and bearings, while the gearbox is still warm.

Use puller no. 502 50 65-01.

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.

The cylinder and the piston are two of the compo- nents exposed to most strain in the engine. They must withstand, for example, high speeds, large tempera- ture swings and high pressure. Moreover, they must be resistant to wear. Despite these tough working conditions, major piston and cylinder failure is rela- tively uncommon. The reasons for this include new coatings in the cylinder bore, new types of oil and grease and refined manufacturing techniques.

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.

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.

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.

Keep your thumb over the circlip to prevent it from flying out.

Dismantle the piston.

Decompression valve

Dismantle the decompression valve.

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.

Clean the decompression valve and check that the valve head is not dam- aged (burnt) and that the valve oper- ates easily.

If necessary, grind the valve with fine- grained valve grinding compound.

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.

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.

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.

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 compres- sor 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.

45

Medium to deep scores along the entire piston skirt on the exhaust side.

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.

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.

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%).

Piston scoring caused by heavy carbon deposits

Too heavy carbon depositing can cause damage similar to that caused by insuffi- cient 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.

Small score marks and a matt, grey surface on the piston???s inlet side caused by fine dust particles.

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.

Larger, softer particles that penetrate into the engine cause damage to the piston skirt under the piston ring as the illustration shows.

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 measure- ment.

Max. 0.15 mm. Clean the groove before checking the measure- ment.

Dismantling

Dismantle all components so that only the crankcase and crankshaft remain.

Dismantle the guard under the crank- case.

Bend away the heat guard (A) and cable guide (B).

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) with your fingers and carefully push the cable guide (B) aside with a screwdriver.

Remove the 4 bolts holding the crank- case halves together.

Remove the 4 bolts holding the crank- case halves together.

Push out the crankshaft from the crankcase half.

Remove the bearing and sealing rings from the crankcase halves.

Fit tool 502 52 39-01 to the clutch side of the crankcase as illustrated.

Separate the crankcase halves.

Fit tool 502 52 39-01 as illustrated.

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.

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.

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.

502 50 30-19

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.

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.

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!

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.

Fit plug 503 55 22-01 instead of the decompression valve.

Connect meter 531 03 06-23 and check for leakage.

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/cm2) 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/cm2).

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/cm2) 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

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

Exhaust gases consisting of Hydrocarbon (HC) Nitrous oxide (NOx) Carbon monoxide (CO) Carbon dioxide (CO2) Particles (PM)

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 desig- nation 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.

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.

Adjustable fuel jets with movement limiters

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 carburet- tor???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).

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