Yamaha YZ250 Handbuch Seite 260

CYLINDER HEAD, CYLINDER AND PISTON
3. Remove:
9 Piston ring 1
NOTE:
Take care not to scratch the piston or damage
the piston ring by expanding it more than neces-
sary.
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.
Warpage limit:
0.03 mm(0.0012 in)
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.
4-21
ENG