Service Manual

Tappet Adjustment
The engine is equipped with adjustable valve tappets.
The valve tappet clearance should be checked and
as specified in the
Periodic Maintenance
Schedule
(located in the Operator’s Manual). Adjust the
valve clearance only when engine is at ambient temper-
ature. Proceed as follows:
1. Remove ignition key to prevent accidental starting.
2. Remove all parts necessary to gain access to valve
tappets.
3. Remove spark plugs to ease the task of turning the
engine over
by hand.
4. Rotate crankshaft in a clockwise direction until the
right intake valve (viewed from carburetor end)
opens and closes. Continue turning the crankshaft
until the flywheel timing mark is lined up with the
governor shaft on the gear cover. This should place
the right piston
(#1) at the top of its compression
stroke. Verify that the left intake and exhaust valves
are closed and there is no pressure on the valve
lifters.
5. The correct feeler gauge for the valve adjustment
(see SPEClFlCATIONS) should pass freely between
valve cap and tappet; a
0.002 inch (0.05 mm) thicker
gauge should not (Figure
1).
6. To correct valve clearance, use a 7/16 inch open
end wrench
to turn the adjusting screw to obtain the
correct clearance. The screw is self-locking and
will stay where
it is set. A 9/16 inch (14 mm) open
end wrench is required to hold the tappet while
7. To adjust valves on the left hand cylinder, turn
engine one complete revolution and again line up
the flywheel timing mark with the governor shaft on
the gear cover. Then follow adjustment procedure
given for right hand cylinder.
8. Replace all parts removed in Step 2. Tighten all
screws securely. Torque valve cover bolts
to speci-
fied torque.
turning the adjusting screw.
VALVE SYSTEM
A properly functioning valve system is essential for good
engine performance.
All engines utilize an L-head type
valve design as shown in Figure
1. Access to the valve
system can be obtained by removing the cylinder heads
and the valve covers.
A valve spring compressor must
be used
to remove valves from the cylinder block.
A valve stem seal is used on the intake valve guides.
This seal must be replaced each time the valve
is
removed.
Place valves, springs, retainers, and tappets in a rack as
they are removed from cylinder block
so they can be
identified and reinstalled in their original locations.
Discard old valve stem seals and replace with new ones
during assembly.
Use the following procedures
to inspect and service the
valve system.
Inspection
Clean carbon from the valves, valve seats, valve guides,
and cylinder block.
Valves: Check the valve face for evidence of burning,
warpage, out-of-round, and carbon deposits.
Burning and pitting are caused by the valve failing
to
seat tightly. This condition is often caused by hard
carbon particles on the seat.
It may also be due to weak
valve springs, insufficient tappet clearance. warpage,
and misalignment.
VALVE STEM SEAL VALVE CLEARANCE
VALVE ADJUSTING
\ SCREW
VALVE SEAT INSERT
FIGURE 1. INTAKE VALVE ASSEMBLY
CLEARANCE
VT-1000
VT-1034