use a spark plug thread tap (
Figure 30
) to clean the
threads. If the damage is severe, restore the threads
by installing a steel thread insert. Thread insert kits
can be purchased at automotive supply stores or
they can be installed at a Yamaha dealership.
5. After all carbon is removed from the combustion
chambers and valve ports, clean the entire head in
solvent.
6. Clean away all carbon on the piston crowns. Do
not remove the carbon ridge at the top of the cylin-
der bore.
NOTE
The intake manifolds are not inter
changeable. Mark each manifold be
fore removal so it will be reinstalled
on the correct cylinder head during
assembly.
7. Inspect the intake manifolds (
Figure 31
) for
cracks or other damage that would allow unfiltered
air into the engine. If necessary, remove the mani-
folds and discard the O-rings. Reinstall the mani-
folds with new O-rings. Install each manifold in its
original location and tighten the mounting bolts to
10 N•m (89 in.-lb.).
8. Check for cracks in the combustion chambers
and exhaust ports. If necessary, remove the exhaust
manifold from the rear cylinder. A cracked head
must be replaced.
9. Inspect the threads on the exhaust pipe mounting
studs (A,
Figure 32
). Clean the threads with an ap-
propriate size metric die. Replace a stud if the dam-
age is severe.
10. After the head has been thoroughly cleaned,
place a straightedge across the gasket surface at
several points. Measure the warp by inserting a
feeler gauge (B,
Figure 32
) between the straight-
edge and the cylinder head at each location. If warp
exceeds the service limit listed in
Table 2
, the cylin-
der head must be replaced or resurfaced. Consult a
Yamaha dealership or machine shop experienced in
this type of work.
11. Visually inspect the cam chain tensioner as-
sembly (
Figure 33
) for wear or damage. If any part
is damaged, replace the chain tensioner assembly.
12. Check the chain tensioner operation as follows:
a. Insert a screwdriver in the tensioner body.
b. Turn the screwdriver clockwise until the
plunger completely retracts and locks in
place. See
Figure 25
. The pushrod should
move smoothly.
c. Release the plunger by turning the screw-
driver slightly counterclockwise.
d. The pushrod should fully extend from the
tensioner body.
13. Inspect the cam sprockets (
Figure 34
) for wear
or missing teeth. Replace the sprocket if necessary.
NOTE
If a cam sprocket is worn, also inspect
the cam chain, chain guides and the
98
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