Service Manual

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: Free rotating valves are used for intake
and exhaust. While in the open position, the valves must
rotate freely.
Valve Seats: Inspect valve seat inserts. If seats are in
serviceable condition clean seat up by using either a
seat cutter
or seat grinder. 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
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 on
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
VALVE SEAT
(USE PROPER TOOL)
INSERT DRIVER
CHECK THIS SURFACE
FOR BURRS BEFORE
INSERTING SEAT
VT-1025
FIGURE 5. INSERTING NEW VALVE SEAT
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 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.
Use Onan valve seat staker
only.
PULLER JAWS 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 seat securely in
place.
It will be necessary to refinish valve seat inserts
C-1104
FIGURE 4. VALVE SEAT REMOVAL before installing valves.
10-4