Section IV. MAIN BEARINGS AND CRANKSHAFT

f. Temporarily install the connecting rod cap

e. When securing the connecting rod (28) and

(21, fig. 4-1) on the connecting rod and torque the

cap (21) in the crankshaft journal, check that the

cap screws (18) to 12 foot-pounds. Use plastigage

match marks on the parts are alined and that they

or other means of determining the running

are toward the bearing plate end of the engine.

clearance between the crankpin and the connecting

Refer to figure 4-6. Make sure the bearing journal

rod. Running clearance shall be 0.001 to 0.0025

is thoroughly lubricated.

inch. If running clearance is excessive, check the

dimensions given in table 4-1 to determine if the

crankshaft or the connecting rod must be replaced.

g. Secure the connecting rod cap (21) to the

connecting rod (28) with cap screws (18), flat

washers (19), and the lock (20). Torque the cap

screws to 12 foot-pounds. After tightening, bend

tangs of the lock against a flat of the screws to lock

them in place.

h. When installing the oil pan (16), be sure to

use a new gasket (17). Tighten the cap screws (15)

evenly and alternately to prevent gaps in the gasket

which could result in oil leaks.

i. Install the cylinder head on the engine (para 4-

6).

j. Install the centrifugal pump on the engine

(para 3-4).

Figure 4-6. Connecting rod and cap matching and positioning

marks.

Section IV. MAIN BEARINGS AND CRANKSHAFT

4-11. Description

piston assembled, minimizing vibration as the

a. The crankshaft rides in two ball bearings, one

crankshaft rotates. The toothed segment of the

at each end of the crankshaft. The bearing at the

crankshaft engages the camshaft gear to drive the

power takeoff end of the shaft is seated in the

crankshaft and governor.

bearing bore of the cylinder block. The bearing at

4-12. Removal and Disassembly

the flywheel end of the shaft is seated in a bearing

a. Remove the air cleaner, muffler, fuel tank and

plate which is bolted to the cylinder block. Both

lines, and carburetor. (TM 5-4320-259-12).

bearings are lubricated by splash as the dipper on

b. Remove the centrifugal pump from the engine

the connecting rod cap dips into the engine oil in

(para 3-2).

the oil pan with each revolution of the crankshaft,

c. Remove the piston and connecting rod (para

dispersing oil throughout the interior of the engine.

4-8).

b. Since both ends of the crankshaft extend from

d. Remove the flywheel and magneto (TM 5-

the crankcase, it is necessary to provide shaft seals

4320-259-12).

to prevent oil leakage around the shaft. These are

e. Remove the four cap screws (2, fig. 4-7), lock

lip-type seals, one of which is pressed into the

washers (3), and flat washers (4) that secure the

cylinder block bore and the other into the bearing

bearing plate (5) to the cylinder block (23).

plate bore.

Remove the bearing plate. If necessary, use a puller

c. The crankshaft is counterbalanced to

as shown in figure 4-8 to remove the bearing plate.

counteract the weight of the connecting rod and

Remove the gasket (6, fig. 4-7).

4-6