Yamaha RS90K Manuel D'atelier page 468

3 7 5
2 6 8
2
1
CYLINDER HEAD
REMOVAL
1. Remove:
1 • Cylinder head bolts
NOTE:
Loosen each bolt 1/2 of a turn at a time. After all of
the bolt are fully loosened, remove them.
4
INSPECTION
1. Eliminate:
• Combustion chamber carbon deposits
(with a rounded scraper)
NOTE:
Do not use a sharp instrument to avoid damaging
or scratching:
• spark plug bore threads
• valve seats
2. Check:
• Cylinder head
Damage/scratches → Replace.
• Cylinder head water jacket
Mineral deposits/rust → Eliminate.
3. Measure:
• Cylinder head warpage
Out of specification → Resurface the cylinder
head.
Measurement steps:
• Place a straightedge 1 and a thickness gauge
2 across the cylinder head.
• Measure the warpage.
• If the limit is exceeded, resurface the cylinder
head as follows.
• Place a 400 ~ 600 grit wet sandpaper on the
surface plate and resurface the cylinder head
using a figure-eight sanding pattern.
NOTE:
To ensure an even surface, rotate the cylinder head
several times.
5-25
ENG
Maximum cylinder head warpage:
0.10 mm (0.0039 in)