Section VI. CAMSHAFT, BUSHINGS, AND DRIVE GEAR

TM 10-3930-621-34

(4) Check counterbore for cleanliness and

Caution: The crush for any given seat and

freedom from burr edges.

engine combination is a very critical dimension.

(5) Using a pair of forceps or a hooked wire,-

Attempts to over-crush seats frequently result in the

quickly lift the chilled seat from the dry ice bath and

seat loosening during service.

locate it over the counterbore so the chamfer of the seat

(a) Subtract the original counterbore diameter from the

lower edge is entered squarely.

original seat diameter.

(6) Start the driving mandrel pilot in the valve

(b) Measure the diameter of the new seats and

guide, bring the driving face against the seat upper

subtract the figure obtained for the crush ( (a) above).

surface accurately, and tap the mandrel firmly with a

medium weight hammer.

obtained above and enlarge the counterbore.

(7) If severe hammering is required, the

(2) Place seat in a container filled with alcohol or

counterbore is not the correct size, the seat was not

gasoline and several chunks of dry ice.

chilled enough, or the seat was not started into the

(3) Slip a sturdy washer-like driving plate, somewhat

counterbore straight.

larger than the seat, over the madrel pilot of a seat

driving tool.

Note. Peening seats in position is no longer a standard

production procedure, and therefore is not necessary.

Section VI. CAMSHAFT, BUSHINGS, AND DRIVE GEAR

3-21. Description

3-41), timing gear cover (para 3-37a), and distributor,

The camshaft runs in steel backed babbit shells located

fuel pump and valve covers (TM 10- 3930-621-12).

in the three main crankshaft bulkheads. The camshaft

b. Raise valves and springs (1, 4, fig. 3-6), and keep

drive gear is pressed and keyed on the front end of the

them raised with wooden blocks or other suitable means.

camshaft. Two spiral gears are provided, one to) drive

c. Raise tappets (8) to clear cam lobes on shaft. Keep

the oil pump and the other to drive the distributor. An

tappets raised with tape, wire, cord or by other suitable

eccentric, toward the rear of the camshaft, actuates the

means.

diaphragm type fuel pump. Camshaft end play is

d. Remove the two thrust plate screws (15) through

controlled by a thrust plate (19, fig. 3-6) located between

holes in drive gear (16).

the shoulder of the rear cam journal and the face of the

e. Gently withdraw camshaft from its sleeve bearings

drive gear hub (16). The drive gear is secured to the

(9, 10 and 22). See figure 3-7.

camshaft by a retaining ring (17).

Caution: Do not allow cam lobes to catch or,

3-22. Removal and Inspection

be scratched by, or scratch, sleeve bearings.

a. Remove oil pan (para 3-40), oil pump (para

3-10