Cleaning and Inspection - TM-5-4320-259-340023

Insert the valves in the valve seats as shown in

d. With the crankcase breather removed, the

figure 4-2 and check the clearance between the

lower ends of the valves are accessible. Use a valve

valve stems and valve tappet with a feeler gage.

spring compressor to compress the valve springs.

With the valve held firmly on the valve seat, the

Remove the valve retaining pins (6 and 10) and

valve clearance with the engine cold shall be 0.005

carefully release the valve springs. Pull the valves

to 0.009 inch for intake valves and 0.011 to 0.015

(7 and 11) out of the top of the engine. Remove the

inch for exhaust valves. If clearance is insufficient,

springs (9 and 13) and valve rotators (8 and 12)

grind off the bottom of the valve to meet the

from the valve chamber.

requirement. Make sure the valve ends are ground

4-5. Cleaning and Inspection

square and are free of burrs.

a. Clean all parts with an approved cleaning

solvent; dry thoroughly.

b. Scrape all carbon deposits from the cylinder

head with a putty knife or other bladed instrument.

Take care not to score or gouge the gasket surface

of the cylinder head.

c. Inspect the cylinder head for cracks, burning,

broken cooling fins, and other damage. Check the

cylinder head for flatness by laying it on a true flat

surface. Attempt to insert feeler gages under the

edges of the cylinder head to determine if it is

warped. Slight warping can be corrected by

resurfacing. To resurface, lay a piece of fine sand-

paper on a true flat surface and rub the cylinder

head against the sandpaper. Do not remove more

material than is necessary to correct the warping.

d. If the spark plug insert in the cylinder head

has defective threads, press out the insert and

replace with a new one.

e. Inspect the valves for worn or bent stems,

rough, checked, burned, or distorted valve heads,

and enlarged mounting pin holes. Check the fit of

the valve stems in the bores of the cylinder block.

Figure 4-2. Checking valve clearance.

Intake valve side clearance shall be 0.0005 to

0.0020 inch. Exhaust valve side clearance shall be

b. When installing the valve springs (9 and 13,

0.0020 to 0.0035 inch.

fig. 4-1), use a valve spring compressor and insert

f. Check valve head diameter. Intake valve head

the valve retaining pins (6 and 10).

diameter shall be 0.979 to 0.989 inch. Exhaust

c. Check that the valve rotators (8 and 12)

valve head diameter shall be 0.807 to 0.817 inch.

provide proper rotation of the valves as the valves

g. Check the valve seat in the cylinder block.

are lifted by the valve tappets.

Valve seat width shall be 0.037 to 0.045 inch for

d. When installing the cylinder head (3), be sure

both intake and exhaust valves. Use a 15-degree

to use a new gasket (4). Tighten the cylinder head

cutter if necessary to narrow the valve seat.

bolts (1) to 16 to 17 foot-pounds. Tighten the bolts

h. Check the fit of the valves in the valve seats in

in the sequence shown in figure 4-3.

the block. A tight seal must be made. If necessary,

regrind the valves and valve seats. The valve head

angle is 45 degrees for both valves. The valve seat

angle is 89 degrees for both valves. Lap the valve to

the seat, using fine grade of grinding compound

and a hand valve grinder with a suction cup.

i. If the valve seat in the cylinder block cannot

be properly reground, replace the valve seat as

directed in paragraph 4-21 d.

4-6. Reassembly and Installation

Reassemble and install the valves and cylinder

Figure 4-3. Cylinder head bolt tightening sequence.

head as shown in figure 4-1. Note the following:

a. Make sure the valve seats, ports, and valves

are thoroughly cleaned after regrinding or lapping.

4-3