Section II. CYLINDER HEAD AND VALVES

Table 4-1. Engine Fits, Tolerances, and Wear Limits--Continued

Dimension (in.)

Item

0.0007/0.0022

Ball bearing to seal plate (interference)

0.0004/0.0003

Ball bearing to crankshaft (interference to loose)

Section Il. CYLINDER HEAD AND VALVES

4-3. Description

a. The cylinder head is mounted on top of the

cylinder/block to seal the cylinder and to provide a

mounting for the spark plug. The cylinder head is

deeply finned to provide efficient dissipation of heat

caused by combustion in the cylinder.

b. The valves are mounted in the cylinder block

and are opened at the required time by cams on the

camshaft through valve tappets mounted in the

cylinder block. The valves are heavily spring loaded

to close when disengaged by the cams on the

cam shaft. The valves use positive valve rotators to

assure that the valves rotate a small amount each

time they are operated. This equalizes valve wear

and causes a wiping action which helps to assure a

good valve seat when the valves close.

4-4. Removal and Disassembly

a. Remove the pump from the engine (para 3-2).

b. Remove the spark plug, engine housing, and

the crankcase breather (TM 5-4320-259-12).

c. Make sure the engine is cooled to room

temperature. Remove the six bolts (1, fig. 4-1) and

flat washers (2) that secure the cylinder head (3) to

the cylinder block. Remove the cylinder head and

gasket (4).

KEY to fig. 4-1:

1. Cylinder head bolt

15.

Assembled washer screw

2. Flat washer

16.

Oil pan

3. Cylinder head

17.

Oil pan gasket

4. Cylinder head gasket

18.

Connecting rod cap screw

5. Spark plug insert

19.

Flat washer

6. Valve retaining pin

20.

Lock

21.

Connecting rod bearing cap

7. Intake valve

8. Valve rotator

22.

Compression ring

9. Valve spring

23.

Compression ring

10. Valve retaining pin

24.

Oil control ring

11. Exhaust valve

25.

Retainer ring

12. Valve rotator

26.

Piston pin

27. Piston

13. Valve spring

14. Oil pan drain plug

28. Connecting rod

Figure 4-1. Cylinder head, valves, and pistons, exploded view.

4-2