Yamaha WR250FM service manual Inspection, Cylinder head

CYLINDER HEAD

ENG

INSPECTION

Cylinder head

1.Eliminate:

•Carbon deposits

(from the combustion chambers) Use a rounded scraper.

NOTE:

Do not use a sharp instrument to avoid damag- ing 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 resurfacing 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.

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