Yamaha YFM7FGPW Service Manual page 194

CYLINDER AND PISTON
2. Measure:
• piston-to-cylinder clearance
M MMM M MMM M
a. Measure the cylinder bore "C" with a cylin-
der bore gauge.
NOTE:
_
Measure the cylinder bore "C" in parallel to and
at right angles to the crankshaft. Then, find the
average of the measurements.
Cylinder bore
"C"
Taper limit "T"
Out of round
"R"
"C" = Maximum D
"T" = (Maximum D
– (Maximum D
"R" = (Maximum D
– (Minimum D
b. If out of specification, replace the cylinder,
and the piston and piston rings as a set.
c. Measure piston skirt diameter "P" with the
micrometer.
a 10 mm (0.39 in) from the bottom edge of the pis-
ton
Piston size "P"
Standard
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
0.030 ~ 0.055 mm
(0.0012 ~ 0.0022 in)
<Limit>: 0.13 mm (0.051 in)
4 - 36
ENG
M MMM M M MMM M M MMM M M MMM
102.000 ~ 102.010 mm
(4.0157 ~ 4.0161 in)
0.05 mm (0.002 in)
0.05 mm (0.002 in)
or D )
1 2
or D )
5 6
, D or D )
1 3 5
, D or D )
2 4 6
101.955 ~ 101.970 mm
(4.0140 ~ 4.0146 in)
M MMM