Valve Tappets

TM 10-3930-621-34

(3) Before grinding valves, make sure the valve

old guide. Break off old guides as they are forced out to

stems and guides are a good fit, within tolerances, to

allow clearance. If required, the valve seat should be

ensure a concentric seat and a tight valve.

removed prior to guide removal (para 3- 20).

(4) Apply a good, medium grinding compound

c. Installation.

sparingly around the entire valve seat. Slip a light lifting

(1) Press new guides into place with a suitable

spring over the stem, lubricate the stem and place the

arbor press and mandrel.

valve in its original position. The spring should just

(2) Press guide in until upper end is 1.0 inch

barely h d the valve off its seat.

from the face of the engine block.

(5) Place the grinding tool cup on the head of

the valve. Press down until the valve is seated. Turn the

Note. Special notice should be taken of the exhaust

valve until all the grinding compound is rubbed off the

valve guide and valve stem shoulder. The guide should

valve seat. Release the pressure on the valve and the

not project into the gas passage and the stem shoulder

light spring will lift it clear of its seat.

should be sharp and located slightly below the end of the

(6) Withdraw the valve and put on fresh grinding

guide when the valve is seated. Thus any accumulation

compound and repeat the grinding operation. Valve seat

of carbon around the guide and stem running surfaces

angle must be 45 and the valve face diameter must not

will be sheared away each time the valve it lifted.

be less than the seat inside diameter of 1.214 to 1.224

inches.

(3) Refer to TM 10-3930-621-12 and install cylinder

(7) Clean the valve and its seat occasionally to

head.

see how the grinding is progressing. When all the pits

3-19. Valve Tappets

and grooves have disappeared, clean the valve and

a. Removal.

valve seat, and place eight or ten equally spaced marks

(1) Remove camshaft (para 3-22).

with a soft lead pencil on the seat. Insert the valve, give it

(2) Remove valve tappets (8,fig.3-6), through

a quarter turn, and remove it. A perfect seat will be

bottom of crankcase.

indicated if every pencil mark shows where the valve has

b. Inspection and Cleaning.

rubbed it. If any of the pencil marks are left untouched,

(1) Soak tappets in a cleaning compound,

continue the grinding.

solvent (Spec.

P-S-661), and remove any foreign

(8) When the grinding is completed, check the

material. Dry thoroughly with compressed air.

valve seat in relation to the valve guide for concentricity

(2) Inspect for warping, cracks, wear or other

with a dial indicator. Total run out of the seat from the

damage.

valve guide should not exceed 0.0020 inch total indicator

(3) When worn or damaged tappet is found,

reading.

always check camshaft lobe (para 3-19). Valve tappet

(9) Clean all traces of grinding compound from

running clearance in the crankcase is from 0.002 to

the valve chamber and ports, oil the valve stem and

0.0005 of an inch.

install. Remember to install each valve in the same

(4) Replace damaged parts as authorized.

position from which it was removed.

c. Installation. Oil the tappet and install, checking it for

d. Installation.

free movement in the block. Install camshaft (para 3-

(1) Insert valve in guide (2, 3, fig. 3-6) and cap

24).

to which it has been fitted.

3-20. Valve Seats

(2) Install spring (4) and retainer cap (7),

a. Removal.

compress spring and insert wedge shaped locks (6)

(1) If seat is peened in position, use a suitable

between concave side of retainer cap and groove in

cutter to remove the metal from the block that is peened

valve stem.

over the seat.

(3) Releasing the spring holds the locks (6) in

(2) Using a seat puller, remove seat from the

place and holds the spring on the stem. (4) Install valve

engine block. Discard seat.

covers and cylinder head (TM 10-3930-621-12).

b. Cleaning. Using a suitable cutter with a radius of

3-18. Guides

0.015 to 0.020 of an inch smaller than counterbore, clean

Description. Valve guides are tubular inserts

up the counterbore. There must be no sharp break

designed for press fit insertion into the engine block.

where the counterbore wall meets the bottom surface.

b. Removal. Refer to TM 10-3930-621-12 and

c. Installation.

remove cylinder head. Refer to paragraph 3-17 and

(1) Enlarge the seat counterbore as follows to obtain

remove valves. The guide may be reamed to leave only

the correct size or crush for the new over- sized seat.

a thin shell. Collapse the shell to remove the

3-9