Checking The Cylinder Head - Yamaha YFM250RX 2008 Service Manual

CYLINDER HEAD

CHECKING THE CYLINDER HEAD

1. Eliminate:
• Combustion chamber carbon deposits
(with a rounded scraper)
NOTE:
Do not use a sharp instrument to avoid damag-
ing or scratching:
• Spark plug bore threads
• Valve seats
2. Check:
• Cylinder head
Damage/scratches → Replace.
3. Measure:
• Cylinder head warpage
Out of specification → Resurface the cylin-
der head.
Warpage limit
0.05 mm (0.0020 in)
a. Place a straightedge
gauge across the cylinder head.
b. Measure the warpage.
c. If the limit is exceeded, resurface the cylin-
der head as follows.
d. Place a 400–600 grit wet sandpaper on the
surface plate and resurface the cylinder
head using a figure-eight sanding pattern.
NOTE: NOTE:
To ensure an even surface, rotate the cylinder
head several times.
4-10
ENG
and a thickness