Yamaha WR250F(N), Owner'S Service Manual

Page: 326 / 686

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ENG
CYLINDER HEAD
INSPECTION
Cylinder head
1. Eliminate:
●
Carbon deposits (from the combustion
chambers)
Use a rounded scraper.
NOTE:
Do not use a sharp instrument to avoid dam-
aging or scratching:
●
Spark plug threads
●
Valve seats
2. Inspect:
●
Cylinder head
Scratches/damage
→
Replace.
3. Measure:
●
Cylinder head warpage
Out of specification
→
Resurface.
Cylinder head warpage:
Less than 0.05 mm (0.002 in)
Warpage measurement and resurface-
ment steps:
●
Place a straightedge and a feeler gauge
across the cylinder head.
●
Use a feeler gauge to measure the
warpage.
●
If the warpage is out of specification,
resurface the cylinder head.
●
Place a 400 ~ 600 grit wet sandpaper on
the surface plate, and resurface the head
using a figure-eight sanding pattern.
NOTE:
To ensure an even surface rotate the cylin-
der head several times.