Checking The Piston Rings - Yamaha UMAX Service Manual

Bore
85.000–85.020 mm
(3.3465–3.3472 in)
Wear limit
85.050 mm (3.3484 in)
"C" = maximum of D , D
1
b. If out of specification, rebore or replace the
crankcase, and replace the piston and pis-
ton rings as a set.
c. Measure piston skirt diameter "P" with the
micrometer.
Piston
Diameter
84.977–84.998 mm
(3.3456–3.3464 in)
P
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 "P"
Piston-to-cylinder clearance
0.043–0.057 mm
(0.0017–0.0022 in)
, D , D , D , D
2 3 4 5 6
CRANKSHAFT AND PISTON
f. If out of specification, rebore or replace the
crankcase, and replace the piston and pis-
ton rings as a set.

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.
Piston ring
Top ring
Ring side clearance
0.040–0.080 mm
(0.0016–0.0031 in)
2nd ring
Ring side clearance
0.030–0.070 mm
(0.0012–0.0028 in)
2. Install:
• Piston ring
(into the cylinder)
TIP
Use the piston crown to level the piston ring near
bottom of cylinder "a", where cylinder wear is
lowest.
b. Upper of cylinder
5-30
a
b