if necessary.
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All machines
: Pry out the plugs (arrows).
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: Take out the screws (arrows).
– Remove the muffler.
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: Remove the gasket (1) and heat shield (2).
– Clean the sealing faces.
Reassemble in the reverse sequence.
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: Fit the heat shield (2) in position.
: Install the new gasket (1) so that its bead (A) faces outwards.
– Fit the muffler.
– Tighten down the screws firmly – b 3.5
5.7 Bar Mounting Studs 6. Engine
6.1 Muffler/Spark Arresting Screen
Online version - not for reprint
– Unscrew the spark plug – b 5.4 : Loosen the slotted nut (1).
: Lift the shroud (2) away vertically.
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2
– Before fitting the shroud, check that the grommets (arrows) are properly seated.
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– Before fitting the shroud, check that cap (arrow) and grommet (1) are properly seated.
– On machines without
decompression valve, check that cap (2) is properly seated.
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1
Always replace damaged caps and grommets in sets.
– Fit the shroud and tighten down the slotted nut firmly – b 3.5
Defective oil seals and gaskets or cracks in castings are the usual causes of leaks. Such faults allow supplementary air to enter the engine and upset the fuel-air mixture.
This makes adjustment of the prescribed idle speed difficult, if not impossible.
Moreover, the transition from idle speed to part or full throttle is not smooth.
The crankcase can be checked thoroughly for leaks with the carburetor and crankcase tester and the vacuum pump.
6.2 Shroud 6.3 Leakage Test
Online version - not for reprint
– Remove the shroud – b 6.2 – Remove the decompression
valve, if fitted – b 6.8
: Install plug (1) 1122 025 2200 and tighten down to 25 Nm.
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: Fit spark plug (2) and tighten it down firmly – b 3.5
– Loosen the muffler screws lightly – b 6.1
: Fit sealing plate (1)
0000 855 8106 between the heat shield and cylinder exhaust port
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The sealing plate must completely fill the space between the two screws.
– Remove the switch shaft – b 10.1
– Remove the carburetor – b 12.2.1
– Set the piston to top dead center.
This can be checked through the inlet port.
: Check that the sleeve (1) and washer (2) are in place.
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2
: Fit the test flange 1128 850 4200 (1).
: Fit the sleeves (2) 0000 963 1001.
: Fit nuts (3) and tighten them down firmly.
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1 2
6.3.1 Preparations
Online version - not for reprint
– Preparations – b 6.3.1 : Connect pressure hose (1) of
tester 1106 850 2905 to nipple (arrow) on test flange.
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: Pump air into the crankcase with rubber bulb until the gauge (arrow) indicates a pressure of 0.5 bar. If this pressure remains
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– However, if the pressure drops, the leak must be located and the faulty part replaced.
To find the leak, coat the suspect area with oil and pressurize the crankcase. Bubbles will appear if a leak exists.
– After finishing the test, open the vent screw and disconnect the hose of tester 1106 850 2905.
– Continue with vacuum test – b 6.3.3
Oil seals tend to fail when subjected to a vacuum, i.e. the sealing lip lifts away from the crankshaft during the piston's induction stroke because there is no internal counterpressure.
An additional test can be carried out with the vacuum pump to detect this kind of fault. Carry out the same preparations as for the pressure test – b 6.3.2
: Connect suction hose (arrow) of vacuum pump 0000 850 3501 to nipple (arrow) of the test flange.
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: Close the vent screw (1) on the pump.
: Operate lever (2) until pressure
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6.3.2 Pressure Test 6.3.3 Vacuum Test
Online version - not for reprint
If the vacuum reading remains constant, or rises to no more than 0.3 bar within 20 seconds, it can be assumed that the oil seals are in good condition. However, if the pressure continues to rise (reduced vacuum in the crankcase), the oil seals must be replaced, even if no leaks were detected in the pressure test.
– After finishing the test, open the vent screw and disconnect the hose.
– Remove the test flange.
– Install the carburetor – b 12.2.1 – Loosen the muffler screws and
remove the sealing plate.
– Tighten down the muffler screws firmly – b 3.5
– Install the decompression valve, if fitted – b 6.8
Reassemble all other parts in the reverse sequence.
It is not necessary to disassemble the complete crankcase to replace the oil seals.
Flywheel side
– Remove the flywheel – b 7.1.5
– On machines with handle/
carburetor heating, remove the generator – b 14.7
– Free off the oil seal in its seat by tapping it with a suitable tube or a punch.
: Apply puller (1) 5910 890 4400 with No. 6 jaws 0000 893 3711.
– Clamp the puller arms.
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– Pull out the oil seal.
Take care not to damage the crankshaft stub.
– The crankshaft sealing face and taper must be free from grease.
Clean with standard solvent-based degreasant containing no chlorinated or halogenated hydrocarbons – b 16.
– Lubricate sealing lip of oil seal with grease – b 16.
– Slip the oil seal, open side facing the crankcase, over the
crankshaft stub.
: Use the press sleeve (1) 1108 893 2405 to install the oil seal.
The seating face must be flat and free from burrs.
– Wait about one minute, then
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rotate the crankshaft several times.
– Install the generator (if fitted) and tighten down the screws firmly – b 3.5
Reassemble all other parts in the reverse sequence.
Clutch side
– Remove the oil pump – b 11.3.1 6.4 Oil Seals
Online version - not for reprint
: Use pliers 0811 611 8380 to remove the retaining ring (1).
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1
– Free off the oil seal in its seat by tapping it with a suitable tube or a punch.
: Apply puller (1) 5910 890 4400 with No. 3.1 jaws 0000 893 3706.
– Clamp the puller arms.
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– Pull out the oil seal.
Take care not to damage the crankshaft stub.
– Cleaning sealing face with standard solvent-based degreasant containing no chlorinated or halogenated hydrocarbons – b 16.
– Lubricate sealing lip of oil seal with grease – b 16.
: Push the installing sleeve (1) 1118 893 2401 on to the crankshaft stub.
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– Slip the oil seal, open side facing the crankcase, over the
crankshaft stub.
: Use press sleeve (1)
1118 893 2400 to install the oil seal.
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– Remove the installing sleeve.
– Wait about one minute, then rotate the crankshaft several times.
Reassemble all other parts in the reverse sequence.
Before removing the piston, decide whether or not the crankshaft has to be removed as well. The crankshaft has to blocked to remove the flywheel and clutch by resting the piston on the wooden assembly block with the cylinder removed or loosened.
– Remove the muffler – b 6.1 – Remove the shroud – b 6.2 – Remove the fan housing with
rewind starter – b 8.2
– Remove the carburetor – b 12.2.1
– Remove the decompression valve, if fitted – b 6.8 – Remove the spring – b 9.1
: Take the sleeve (1) out of the manifold.
: Remove the washer (2).
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6.5 Cylinder and Piston