Yamaha WR250FM service manual Lapping steps

VALVES AND VALVE SPRINGS

ENG

9.Lap:

•Valve face

•Valve seat

NOTE:

After refacing the valve seat or replacing the valve and valve guide, the valve seat and valve face should be lapped.

Lapping steps:

•Apply a coarse lapping compound to the valve face.

CAUTION:

Do not let the compound enter the gap between the valve stem and the guide.

•Apply molybdenum disulfide oil to the valve stem.

•Install the valve into the cylinder head.

•Turn the valve until the valve face and valve seat are evenly polished, then clean off all of the compound.

NOTE:

For best lapping results, lightly tap the valve seat while rotating the valve back and forth between your hands.

•Apply a fine lapping compound to the valve face and repeat the above steps.

NOTE:

After every lapping operation be sure to clean off all of the compound from the valve face and valve seat.

•Apply Mechanic’s blueing dye (Dykem) to the valve face.

•Install the valve into the cylinder head.

•Press the valve through the valve guide and onto the valve seat to make a clear pattern.

•Measure the valve seat width again. If the valve seat width is out of specification, reface and relap the valve seat.

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