Figure 16. Cylinder head nut tightening sequence.

TM 10-3930-222-20

Figure 16. Cylinder head nut tightening sequence.

b. Remove the spark plugs.

b. Adjustment of valves.

c. With the engine at normal operating

temperature and the throttle and choke valves fully

open, install a compression gage in the spark plug hole.

(1) Using a 1/2-inch valve tappet wrench and

d. Rotate the engine at normal cranking speed (six

a 9/16-inch valve tappet wrench and a

revolutions will be sufficient) to obtain maximum

0.014-inch feeler gage, adjust the valves

compression. Be sure the battery is fully charged and

(fig. 19) of the cylinders in the order of 1

do not rotate the engine more than is necessary to

6-24.

obtain the maximum reading.

(2) Turn the engine until the piston moves to

e. Check the gage for proper reading (at sea level)

top dead center on the compression

of 130 psi. Table II lists the compression readings for

stroke. The intake and exhaust valves

sea level and for altitudes of 1,000 to 10,000 feet above

will be in fully closed position.

sea level.

(3) Slide a feeler gage between the valve

f. Repeat the testing procedure for each cylinder.

tappet adjusting screw and valve stem, A

slight drag should be felt with feeler gage

g. Remove the gage, and install the spark plugs.

when clearance is correct.

(4) To increase clearance, hold valve lifters

Table II. Compression Readings

and turn the adjusting screw to the right.

Altitude above e level

Proper pressure reading

(5) To decrease clearance, hold the valve

(in feet)

(in PSI)

lifters and turn the adjusting screw to the

left.

Sea Level

130

1,000

126.6

c. Installation of Cover.

2,000

119.8

(1) Clean the cover with SD.

8,000

116.2

(2) Reverse procedures in a above to install

4,000

109.8

cover and use a new gasket.

5,000

104.4

24. Compassion Test

6,000

100.0

The compression test is performed to aid in

7,000

94.9

determining the condition of the rings and valves and to

8,000

90.3

determine whether the cylinder head gasket is leaking.,

9,000

85.8

It is performed as follows:

10,000

81.4

a. Start the engine and allow it to idle until it

reaches normal operating temperature.