Inspect And Repair; Reface Valves And Seats; Check Cylinder Head Distortion; Valve Seat Dimensions - Generac Power Systems GTH760 Service Manual

INSPeCT ANd rePAIr

1. Check cylinder head (Figure 5-7). Be sure all gasket material
is removed from surfaces before checking. Use a gasket
scraper if necessary.
a. Inspect cylinder head for cracks or damage.
b. Use a surface plate or straightedge and check cylinder
head mounting surface for distortion.
If mounting surfaces are distorted more than 0.1 mm (.004"),
the cylinder head must be replaced.
Note: It is not recommended that cylinder head mount-
ing surfaces be resurfaced.
Figure 5-7. Check Cylinder Head Distortion
2. Clean the valve guides and measure their I.D. using a split
ball bore gauge (Figure 5-8).
a. Replace head if either valve guide measures 7.06 mm
(0.278 in.) or more.
SPLIT BALL
BORE GAUGE
Figure 5-8. Check valve guides
SeCTIoN 5: CYlINder HeAd ANd vAlveS

REFACE VALVES AND SEATS:

1. Valve seats may be reconditioned using a valve seat
cutter. If valve seat is wider than dimension shown in
Figure 5-9, a narrowing cutter should be used to ensure
that contact area of valve seat is centered on face of
valve (see Figure 5-10).
a. Use a 60° cutter to narrow seat from bottom and a 15°
cutter to narrow seat from top (Figure 5-9).
Note: If valve seat is loose or cracked, replace
cylinder head.
0.8 MM TO 1.2 MM
(1/16" - 3/64")
Figure 5-9. Valve Seat Dimensions
2. Valve faces may be resurfaced to 45°. See Figure 5-10 for
dimensions for valves.
3. Lap valves and seats with a valve lapping tool and valve
lapping compound.
Note: Thoroughly remove all lapping compound before
final assembly.
Note: In most instances it is more economical to replace
the valves than to reface them.
1.2 MM TO 1.6 MM
(3/64" - 1/16")
SEATING AREA CENTERED
ON VALVE FACE
Figure 5-10. Valve Dimensions
5-3
46°
60° CUTTER
15° CUTTER
1/32"
MINIMUM
45° VALVE FACE ANGLE
5