Yamaha XZ550RJ 1982 Service Manual page 56

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If the seat is too narrow and down near the
bottom edge of the valve face, then first use
the 60° cutter and then the 45° cutter.
Lapping
The valve/valve seat assembly should be
lapped if neither the seat nor the valve face is
severely worn.
1. Apply a small amount of coarse lapping
compound to the valve face. Insert the valve
into the head. Rotate the valve until the
valve and valve seat are evenly polished.
Clean off the coarse compound, then follow
the same procedure with fine compound.
Continue lapping until the valve face shows
a complete and smooth surface all the way
around. Clean off the compound material.
Apply bluing dye to the valve face and seat,
and rotate the valve. Check for full seat con-
tact which is indicated by a grey surface all
around the valve face where the bluing has
been rubbed away.
2. After all work has been performed on the
valve and valve seat and all head parts
have been assembled, check for proper
valve/valve seat sealing by pouring solvent
into each of the intake ports, then the ex-
haust ports. There should be no leakage
past the seat. If fluid leaks, disassemble
and continue to lap with fine lapping com-
pound. Clean all parts thoroughly; reas-
semble and check again with solvent. Re-
peat this procedure as often as necessary
to obtain a satisfactory seal.
Valve springs
This engine uses two springs of different sizes to
prevent valve float or surging. The valve spring
specifications show the basic value characteristics.
1. Even though the spring is constructed of du-
rable spring steel, it gradually loses some of
its tension. This is evidenced by a gradual
shortening of free length. Use a vernier
caliper to measure spring free length. If the
free length of any spring has decreased
more than 2mm (0.080 in) from its specifica-
tion, replace it.
2. Another symptom of spring fatigue is insuf-
ficient spring pressure. This can be checked
with a
gauge. Test each spring individually. Place
a spring in the gauge and note the spring
pressure when the spring is compressed to
the installed length (valve closed). If the
pressure does not equal the specified value,
replace the spring.
Valve spring specifications
Free length
Installed length
(valve closed)
Installed pressure
(valve closed)
Allowable tilt from
vertical
valve-spring-compression-rate
Outer spring Inner spring
36.63 mm 36.17 mm
(1.442 in) (1.424 in)
32.0 mm 30.5 mm
(1.26 in) (1.20 in)
14.6kg 8.5kg
(32.2 Ib) (18.7 Ib)
←
2.5º
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