42 – English
PISTON and CYLINDER
Fig. 7
Fig. 6
Max. 1 mm
Fig. 4
Fig. 5
Faults and causes
Score marks in the piston. Fig. 6
1. Incorrect carburettor setting. Too high overspeed.
2. Too low octane fuel.
3. Too little, or incorrect oil in the fuel.
Carbon build-up. Fig. 7
1. Incorrect carburettor setting. Too low overspeed.
2. Too much, or incorrect oil in the fuel.
Piston ring breakage
1. Excessive engine speed.
2. Piston ring worn out.
3. Oversized piston ring groove.
2. That the cylinder is free of score marks.
3. That the piston is free of score marks. Minor scratches
can be polished off with fine emery paper.
4. That the piston ring is not burnt into its groove.
5. Measure the wear on the piston ring by placing it at the
bottom of the cylinder and measuring the gap. See fig. 4.
The clearance must not exceed 1 mm.
6. That the needle bearing is undamaged.
7. That the intake manifold is undamaged.
8. Pressure test the decompression valve as follows. See
also fig. 5.
A. Connect tool 502 50 38-01 to the decompression valve.
B. Pump up the pressure to 80 kPa (0.8 bar).
C. Wait 30 seconds.
D. The pressure must not fall below 60 kPa (0.6 bar).
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