Yamaha YZ125(R)/LC, Owner'S Service Manual

Page: 252 / 568

4-20
ENG
CYLINDER HEAD, CYLINDER AND PISTON
EC474000
INSPECTION
EC474102
Cylinder head
1. Eliminate:
9
Carbon deposits
Use a rounded scraper
1
.
NOTE:
Take care to avoid damaging the spark plug
threads. Do not use a sharp instrument. Avoid
scratching the aluminum.
2. Inspect:
9 Cylinder head water jacket
Crust of minerals/Rust
→
Remove.
9 Cylinder head warpage
Out of specification
→
Re-surface.
Warpage measurement and re-surface-
ment steps:
9 Attach a straightedge
1
and a thickness
gauge
2
on the cylinder head.
9 Measure the warpage.
9 If the warpage is out of specification, resur-
face the cylinder head.
9 Place # 400~600 grit wet sandpaper
3
on
the surface plate, and re-surface the head
4
using a figure-eight sanding pattern.
NOTE:
Rotate the cylinder head several times to
avoid removing too much material from one
side.
EC474201
Cylinder
1. Eliminate:
9 Carbon deposits
Use a rounded scraper
1
.
NOTE:
Do not use a sharp instrument. Avoid scratching
the aluminum.
Warpage limit:
0.03 mm(0.0012 in)