Valve Spring:
Check valve springs for cracks, worn
ends, distortion, and tension. If spring ends are worn,
check valve spring retainer for wear. Check for spring
distortion by placing spring on a flat surface next to a
square. Measure height of spring and rotate it against
square edge to measure distortion. If distortion
exceeds
0.06
inch
(1.5
mm) replace spring. Check
spring tension at the installed height for both the
valve open and closed position using an accurate
valve spring tester. Replace any valve spring that is
weak, cracked, worn, or distorted.
Valve Rotators:
Positive type valve rotators prolong
valve life and decrease valve repairs. When func-
tioning properly, the valve is rotated a fraction of a
turn each time it opens. While at open position, the
valve must rotate freely. There is no easy way to
determine if a valve rotator is good or bad. Onan
recommends that valve rotators be replaced at each
major overhaul or if a build-up
of
carbon is noted on
valve face and valve seat.
Valve Seats:
Inspect valve seat inserts.
If
seats are
loose, cracked or severely pitted, new ones must be
installed. Remove valve seat inserts using a valve seat
removal tool. If valve seat insert bores in cylinder
block are damaged or worn
so
that a press fit cannot
be obtained when installing new standard size valve
seat inserts, the bores must be machined for an
oversize seat.
USE
NEW
VALVE
SEAT
TO
ADJUST
PULLER
DEPTH
PULLER
JAWS
FIGURE
4.
VALVE
SEAT
REMOVAL
C-1104
10-4
Valve Seat Removal:
Remove carbon and combustion
deposits from valve seat. Select proper puller size
determined by inside diameter of valve seat. On some
pullers use a new seat as a guide to adjust puller depth
(Figure
4).
Puller jaws must expand into cylinder block
at the point where bottom
of
valve seat insert rests
cylinder block. Position puller on valve seat and tighten
hex nut. Clamp cylinder block to a solid bench. Attach
slide hammer to puller. Tighten hex nut between each
blow with the slide hammer.
VALVE SEAT
i
VALVE SEAT
(USE
PROPER
TOOL
FOR
BURRS
BEFORE
CHECK
THIS
SURFACE
FIGURE
5.
INSERTING NEW VALVE SEAT
VT-1025
Valve Seat Installation:
After the old seat has been
removed, clean out any carbon or metal burrs from the
seat insert recess. Use a valve seat insert driver and
hammer to install the insert (Figure
5).
Drive the valve
seat insert in
so
that the insert enters the recess evenly.
Make certain that the valve seat insert rests solidly on
the bottom of the recess all the way around its
circumference.
To assure a tight valve seat fit and eliminate the danger
of
seat loosening in the bore, valve seat must be staked.
Insert valve seat staker into valve seat or guide in
cylinder block. Using a lead hammer, strike the staking
tool a sharp blow to wedge new valve securely in place.
It will be necessary to refinish valve seat inserts before
installing valves.
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