Yamaha YZ125N1 Service Manual page 107

CYLINDER HEAD, CYLINDER AND PISTON
EC474000
INSPECTION
EC474101
Cylinder head
1. Remove:
9Carbon 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:
9Cylinder head water jacket
Crust of minerals/Rust
9Cylinder head warpage
Out of specification
Warpage measurement and re-surface-
ment steps:
9Attach a straightedge 1 and a thickness
gauge 2 on the cylinder head.
9Measure the warpage.
Warpage limit:
0.03 mm(0.0012 in)
9If the warpage is out of specification, resur-
face the cylinder head.
9Place # 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.
EC474200
Cylinder
1. Remove:
9Carbon deposits
Use a rounded scraper 1.
NOTE:
Do not use a sharp instrument. Avoid scratching
the aluminum.
4-20
ENG
Remove.
Re-surface.