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48 – English
Cleaning and inspection
Clean all parts, scrape off any sealant from the crankcase and
the cylinder’s contact surfaces. Remove carbon deposits from
the following areas:
1. The piston crown.
2. Top of the cylinder bore (inside).
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. Minor 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.
6. That the intake manifold is undamaged.
7. That the bearings and their rubber seals are undamaged.
CRANKSHAFT, PISTON AND CYLINDER
Faults and causes
Score marks on the piston
1. Incorrect carburettor setting. Too high overspeed.
2. Too low octane fuel.
3. Too low or incorrect oil in the fuel.
Carbon build-up
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.
8. That the big-end bearing does not have any radial play.
Axial play is permitted.
9. That the big-end bearing does not have any score marks or
is discoloured on the sides.
10. That the bearing surfaces for the little-end does not have
any score marks or is discoloured.
11. Crankshaft cannot be reconditioned. In the event of dam-
age the crankshaft must be replaced.
12. That the crankcase is not cracked.