Yamaha XT550J Service Manual page 51

I '
3. Inspect the end of the valve stem. If the
end appears to be "mushroomed" or
has a larger diameter than the rest of the
stem, the valve, valve guide, and oil seal
should be replaced.
4.
Place the valve on V-blocks, and
measure the amount of stem runout
with a dial gauge. If it exceeds the max-
imum limit, replace the valve.
Maximum valve stem runout:
0.01 mm (0.0004 in)
Valve guides
If oil leaks into the cylinder through a valve
due to a worn valve guide or if a valve is
replaced, the valve guide should also be
replaced.
NOTE: _ _ _ _ _ _ _ _ _ _ _ _ _
The valve oil seal should be replaced
whenever a valve is removed or replaced.
3-14
1. Measure the valve guide inside diameter
with a small bore gauge. If it exceeds the
limit, replace it with an oversize valve
guide.
Guide diameter
(1.0.):
Limit: 7.10 mm (0.280 in)
2. To ease guide removal and reinstallation
and to maintain the correct interference
fit, heat the head to 100
D
e
(212
D
F).
Use
an oven to avoid any possibility of head
warpage due to uneven heating.
3.
Use the valve guide remover and valve
guide installer to drive the old guide out
and drive the new guide in.
NOTE: _ _ _ _ _ _ _ _ _ _ _ _
The valve guide oil seal should be replaced
whenever a valve is removed or replaced.
4. After installing the valve guide, use the 7
mm reamer (special tool P / N. YM-
01227) to obtain the proper valve-guide-
to-valve-stem clearance.
VALVE GUIDE
5. After installing the valve guide in the
cylinder head, the valve seat must be
recut. The valve should be lapped to the
new seat.