TM 5-4310-393-14
E.
Adjust.
CAUTION
Too small a clearance will damage piston, cylinder head, and valves. Too large a
clearance will result in difficult starting.
1.
Adjusting the Cylinder Head (Bumping) Clearance.
a.
Crank engine to dead center position.
b.
Ensure cylinder head surface is free of dirt, carbon, or sealing material residue and place cylinder
head gasket onto cylinder head.
c.
Use a dial indicator to establish true top dead center of the piston.
d.
Place a straight edge across the top of the cylinder and measure the distance between the top of the
cylinder gasket and the top of the piston with a feeler gauge.
e.
Ensure that the bumping clearance is between 0.0216/0.0255 inch (0.549/0.648 mm).
NOTE
Gaskets come in various thickness. If you have a choice between two gaskets, it is
best to use the thickest one. Use only one gasket with the required thickness.
2.
Adjusting the Pushrods.
a.
Adjust
complete
pushrod
(Figure 5-30, Item 1) so dimension "A", measured from
bottom of pushrod to the top of the collar, equals
5.8189/5.8268 inch (147.8/148.0 mm). This adjustment
Is required for proper engagement of complete pushrod
with pinion on decompression shaft.
3.
Adjusting the Tappet Clearance.
a.
Put decompression lever (1) in
START position. (Figure 4-3).
b.
Turn engine clockwise when facing
throttle control lever until compression resistance can be
felt.
c.
Check clearance between rocker
and valve stem with a feeler gauge. Tappet clearance
cold should be 0.004 Inch (0.10 mm). To correct
clearance, loosen nut (2).
d.
Adjust screw (Figure 5-31, Item 3)
with a screwdriver until feeler gauge can be pulled
between rocker and valve stem with very slight
resistance after nut (2) has been tightened
FIGURE 5-30. PUSHROD
FIGURE 5-31. TAPPET ADJUSTMENT
5-24
