Yamaha YFM25RY Automobile User Manual


 
CYLINDER AND PISTON
5-25
EAS24380
REMOVING THE PISTON
1. Remove:
Piston pin clips “1”
Piston pin “2”
•Piston3
ECA13810
Do not use a hammer to drive the piston
pin out.
TIP
Before removing the piston pin clip, cover the
crankcase opening with a clean rag to pre-
vent the piston pin clip from falling into the
crankcase.
Before removing each piston pin, deburr the
clip groove and pin hole area. If the piston
pin groove is deburred and the piston pin is
still difficult to remove, use the piston pin
puller “4”.
2. Remove:
Top ring
2nd ring
•Oil ring
TIP
When removing a piston ring, open the end
gap with your fingers and lift the other side of
the ring over the piston crown.
EAS24400
CHECKING THE CYLINDER AND PISTON
1. Check:
•Piston wall
Cylinder wall
Vertical scratches Rebore or replace
the cylinder, and replace the piston and
piston rings as a set.
2. Measure:
Piston-to-cylinder clearance
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Measure cylinder bore “C” with the cylinder
bore gauge.
TIP
Measure cylinder bore “C” by taking side-to-
side and front-to-back measurements of the
cylinder. Then, find the average of the mea-
surements.
Piston pin puller set
90890-01304
Piston pin puller
YU-01304
Bore “C”
74.000–74.016 mm (2.9134–
2.9140 in)
Wear limit
74.100 mm (2.9173 in)
“C” = Maximum of D1–D6