Yamaha YFM45FAR, Service Manual

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4 - 30
ENG
CYLINDER AND PISTON
3rd step:
●
Find the piston-to-cylinder clearance with the
following formula.
●
If out of specification, rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
*****************************************************
Piston-to-cylinder clearance =
Cylinder bore “C” –
Piston skirt diameter “P”
Piston-to-cylinder clearance:
0.040 ~ 0.065 mm
(0.0016 ~ 0.0026 in)
<Limit>: 0.150 mm (0.0059 in)
CHECKING THE PISTON RING
1.Measure:
●
Ring side clearance
Use a feeler gauge.
Out of specification
→
Replace the piston
and rings as a set.
NOTE:
Clean carbon from the piston ring grooves and
rings before measuring the side clearance.
2.Position:
●
Piston ring
(in cylinder)
NOTE:
Insert a ring into the cylinder and push it
approximately 40 mm (1.6 in) into the cylinder.
Push the ring with the piston crown so that the
ring will be at a right angle to the cylinder bore.
a
40 mm (1.6 in)
Side clearance
Standard Limit
Top
ring
0.03 ~ 0.07 mm
(0.0012 ~ 0.0028 in)
0.12 mm
(0.0047 in)
2nd
ring
0.02 ~ 0.06 mm
(0.0008 ~ 0.0024 in)
0.12 mm
(0.0047 in)