Checking The Piston Rings - Yamaha YFM70RY Service Manual

Bore
102.000–102.010 mm (4.0157–
4.0161 in)
Wear limit
102.080 mm (4.0189 in)
Taper limit
0.05 mm (0.002)
Out of round limit
0.05 mm (0.002 in)
b. If out of specification, replace the cylinder,
and replace the piston and piston rings as a
set.
c. Measure piston skirt diameter D "a" with the
micrometer.
a. 10 mm (0.39 in) from the bottom edge of the
piston
Diameter D
101.955–101.970 mm (4.0140–
4.0146 in)
d. If out of specification, replace the piston and
piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
• Piston-to-cylinder clearance =
Cylinder bore "C" –
Piston skirt diameter "D"
Piston-to-cylinder clearance
0.030–0.055 mm (0.0012–0.0022
in)
Limit
0.13 mm (0.0051 in)
f. If out of specification, rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
L LLL L LLL L L LLL L L LLL L L LLL L L LLL L
CYLINDER AND PISTON
EAS24430

CHECKING THE PISTON RINGS

1. Measure:
• Piston ring side clearance
Out of specification → Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
Top ring
2nd ring
2. Install:
• Piston ring
(into the cylinder)
TIP
Level the piston ring into the cylinder with the
piston crown.
LLL
a. 50.0 mm (1.97 in)
5-28
Ring side clearance
0.030–0.070 mm (0.0012–0.0028
in)
Limit
0.12 mm (0.0047 in)
Ring side clearance
0.030–0.070 mm (0.0012–0.0028
in)
Limit
0.13 mm (0.0051 in)