POWERHEAD
Page 4A-50 90-884294 OCTOBER 2001
CLEANING PISTON RING GROOVES
Keystone (tapered) ring grooves
CAUTION
Care must be taken not to scratch the side surfaces of the ring groove. Scratching
the side surface of the ring groove will damage the ring groove.
1. Use a bristle brush and carbon remover solution to remove carbon from side surfaces.
2. A tool can be made for cleaning the inner diameter of the tapered ring grooves. The tool
can be made from a broken tapered piston ring with the side taper removed to enable
the inside edge of the ring to reach the inner diameter of the groove. Carefully scrape
carbon from inner diameter of ring grooves. Care must be taken not to damage the
grooves by scratching the side surfaces of the grooves.
Piston with two half keystone (half tapered) rings
Enlarged View of
Piston Ring Grooves
a
a-Ring Grooves
MEASURING PISTON ROUNDNESS
Piston has a barrel profile shape and is not a true diameter.
1. Using a micrometer, measure dimension “A” at location shown. Dimension “A” should
be as indicated in chart following.
Piston
Dimension “A”
Standard Piston 3.6210 in. ± .0005 in.
(91-9734 mm ± .0127 mm)
0.015 in. Oversize Piston 3.636 in. ± .0005 in.
(92.354 mm ± .0127 mm)
0.030 in. Oversize Piston 3.651 in. ± .0005 in.
(92.735 mm ± .0127 mm)
2. Using a micrometer, measure dimension “A” at location shown. Dimension “A” should
be 3.6210 in. ± 0.0005 in. for a STANDARD size piston.
a
1.0 in.
(25.4 mm)
a
a-Dimension “A” at RIGHT Angle (90°) to Piston Pin
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