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CRANKSHAFT, PISTON AND CYLINDER
Cleaning and inspection
Clean all parts, scrape off any gasket residue from the crank-
case and cylinder contact surfaces. Remove carbon deposits
from the following areas:
1.
The top of the piston.
2.
The top of the cylinder (bore).
3.
The cylinder exhaust port.
Check the following:
1.
That the cylinder's surface coating is not worn, especially
the upper part of the cylinder.
2.
That the cylinder is free of score marks.
3.
That the piston is free of score marks. Small scratches can
be polished off using fine emery paper.
4.
That the piston ring is not burnt into its groove.
5.
Measure the piston ring wear by placing it in the bottom of
the cylinder bore and measuring the play. Play should not
exceed 1 mm/ 0.039".
6.
That the intake manifold is undamaged.
7.
That the needle bearing and its rubber seals are not
damaged.
8.
That the big end bearing does not have any radial play.
Axial play is acceptable.
9.
That the big end bearing does not have any score marks or
discoloration on the sides.
10. That the little end bearing surfaces are not scored or
discoloured.
11. The crankshaft cannot be renovated . In the event of
damage the entire crankshaft should be replaced.
12. That the crankcase is not cracked.
Faults and causes
Score marks on the piston
1. Incorrect carburettor setting. Max. speed too high.
2. Too low octane fuel.
3. Too little or incorrect oil in the fuel.
Carbon build-up
1. Incorrect carburettor setting. Max. speed too low.
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.
39
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