Valve System - Onan T260G Service Manual

Tappet Adjustment
VALVE SYSTEM
Theengine isequipped with adjustable valve tappets. A properly functioning valve system is essential'
for
The valve tappet clearance should be checked and
good engine performance. All engines utilize an L-
adjusted, if necessary, at least every 200 operating
head type valve design as shown in Figure 1. Access
hours or when poor engine performance is noticed. to the valve system can be obtained by removing
Adjust the valve clearance only when engine is at
cylinder heads and the valve covers on top of the
ambient temperature. Proceed as follows: engine. A valve spring compressor must be used to
1.
2.
3.
4.
5.
6.
7.
8.
Remove ignition key to prevent accidental star-
ting.
Remove all parts necessary to gain access to
valve tappets.
Remove spark plugs to ease the task of turning
the engine over by hand.
Place a socket wrench on the flywheel capscrew
and rotate the crankshaft in a clockwise direction
until the left intake valve (viewed from flywheel
end) opens and closes. Continue turning the
crankshaft until the TC mark on the flywheel is
lined up with the TC mark on the gear cover. This
should place the left 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.
The correct feeler gauge for the valve adjustment
(see SPEClFlCATIONS) should pass freely be-
tween valve stem and tappet; a 0.002 inch
(0.05 mm) thicker gauge should not (Figure 1).
To correct the 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 turning the adjusting screw.
To adjust valves on the right hand cylinder, turn
engine one complete revolution and again line up
mark on the flywheel and the TC mark on the gear
cover. Then follow adjustment procedure given
for left hand cylinder.
Replace all parts removed in Step 2. Tighten all
screws securely. Torque manifold bolts to spec-
ified torque.
VALVE CLEARANCE
remove valves from the cylinder block.
A valve stem seal is sometimes used on the intake valve
guides of some engines. 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.
i
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.
V A L V E ADJUSTINGADIUSTING
VALVE SEAT V A L V E SPRING-
)
\ \ I
V A L V E RETAINER
V A L V E SPRING
VALVE ROTA .TOR
FIGURE 1. VALVE ASSEMBLY
YT-1005
10-2