30/ENGINE - WORK ON INDIVIDUAL PARTS 82
16.12Checking/measuring the piston
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– Check the piston bearing surface for damage.
» If the piston bearing surface is damaged:
– Change the piston and, if necessary, the cylinder.
– Check that the piston ring moves smoothly in the piston ring groove.
» If the piston ring is stiff:
– Clean the piston ring groove.
Tip
Use an old piston ring to clean the piston ring groove.
– Check the piston ring for damage.
» If the piston ring is damaged:
– Change the piston ring.
– Check the piston ring anti-rotation lock for damage and to ensure that it is firmly
seated.
» If the piston ring anti-rotation lock is damaged or loose:
– Change the piston.
– Check the piston pin for discoloration or signs of wear.
» If the piston pin has strong discoloration/signs of wear:
– Change the piston and, if necessary, the piston pin bearing.
– Check the piston pin bearing for damage and wear.
» If there is damage or wear:
– Change the piston pin bearing and connecting rod, if necessary.
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– Measure the piston at a distance from the piston head, at right angles to the pis-
ton pin.
Guideline
Distance 31.5 mm (1.24 in)
Piston - diameter
Size 1 39.455… 39.465 mm (1.55334…
1.55374 in)
Size 2 39.465… 39.475 mm (1.55374…
1.55413 in)
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– Piston size is marked on the piston head.
16.13Determining piston/cylinder mounting clearance
– Check/measure the cylinder. ( p. 81)
– Determine the piston/cylinder mounting clearance. ( p. 82)
– The smallest piston/cylinder mounting clearance is the result of the smallest cylinder bore diameter minus the largest piston diam-
eter. The largest piston/cylinder mounting clearance is the result of the largest cylinder bore diameter minus the smallest piston
diameter.
Guideline
Piston/cylinder - mounting clearance
New condition 0.042… 0.065 mm (0.00165… 0.00256 in)
Wear limit 0.10 mm (0.0039 in)
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