Yamaha WR426F(N) Owner's Service Manual page 422

CYLINDER AND PISTON
3rd step:
Calculate the piston-to-cylinder clearance
with following formula:
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>: 0.1 mm (0.004 in)
If out of specification, replace the cylinder,
and replace the piston and piston rings as
set.
Piston ring
1. Measure:
Ring side clearance
Use a feeler gauge 1.
Out of specification
ton and rings as a set.
NOTE:
Clean carbon from the piston ring grooves and
rings before measuring the side clearance.
Top
ring
2nd
ring
2. Position:
Piston ring
In cylinder.
NOTE:
Insert a ring into the cylinder and push it
approximately 10 mm (0.39 in) into the cylin-
der. Push the ring with the piston crown so that
the ring will be at a right angle to the cylinder
bore.
a 10 mm (0.39 in)
4 - 44
ENG
Replace the pis-
Side clearance
Standard
0.030 ~ 0.065 mm
(0.0012 ~ 0.0026 in)
0.020 ~ 0.055 mm
(0.0008 ~ 0.0022 in)
<Limit>
0.12 mm
(0.005 in)
0.12 mm
(0.005 in)