Tappet Cover And Cam Sprocket Cover; Cylinder And Piston - Yamaha YFM250XL(C) Service Manual

4
INSPECTION AND REPAIR
TAPPET COVER AND CAM SPROCKET
COVER
1.Inspect:
Tappet covers (intake 1 and exhaust 2)
Cam sprocket cover 3
O-rings 4
Cracks/Damage → Replace.

CYLINDER AND PISTON

1.Eliminate:
Carbon deposits
(from the piston crown and ring grooves.)
2.Inspect:
Cylinder and piston walls
Vertical scratches → Rebore or replace
cylinder and piston.
3.Measure:
Piston-to-cylinder clearance
*********************************
Measurement steps:
First steps
Measure the cylinder bore "C" with a cyl-
inder bore gauge 1.
a 40 mm (1.6 in) from the cylinder top
NOTE:
Measure the cylinder bore "C" in parallel to
and at right angles to the cylinder matching
surface. Then, find the average of the mea-
surements.
Cylinder
bore "C"
If out of the specification, rebore or
replace the cylinder, and the piston and
piston rings as a set.
4 - 32
ENG
Standard Wear limit
70.97 ~ 71.02 mm 71.10 mm
(2.794 ~ 2.796 in) (2.799 in)
C= X+Y
2