Yamaha LB50IIAC - Yamaha Piston Ring Inspection

5. Wash piston in solvent and wipe dry.
6. Using an outside micrometer, measure
piston diameter. The piston is cam-
ground and tapered. The only measuring
point is at right angles to the piston pin
holes about 10 mm from bottom of pis-
ton. Compare piston diameter to cylinder
bore measurements.
Piston
maximum diameter subtracted
from minimum cylinder diameter gives
piston clearance. If beyond tolerance.
hone
cylinder to tolerance or re-bore to
next over-size and fit over-size piston.
Min.
Max.
Piston clearance
0.025 mm 0.030 mm
Maximum wear limit
0.1 mm
Piston rings
1. Check rings for scoring. If any severe
scratches are noticed. replace set.
2. Insert each ring
into cylinder. Push
down approximately 20 mm using
piston crown to maintain right-angle to
bore. Measure installed end gap. If
beyond tolerance. replace set.
Min.
Max.
Top ring end gap,
0.15 mm
0.35 mm
installed
2nd ring end gap,
0.15 mm
0.35 mm
installed
3. With rings installed in grooves. insert
feeler gauge between ring side and
groove.
If beyond tolerance, replace
ring
and/or piston as required.
Top/2nd
ring side clearance
Min. Max.
LB50 II AC
0.03
mm 0.05 mm
LB80 II AC
0.02
mm
0.06 mm
4. Check ring expander. If worn ex-
cessively,
or broken, replace ring set.
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