Pistons and Connecting Rods - TM-5-4320-272-340029

CAUTION

holes, clogging, and distortion; replace a damaged

When you push the piston and rod from

screen.

the block, be very careful the connecting

(4) Inspect the gears for chipped or broken

rod does not scratch or mar the

teeth, scoring, and wear. Replace any damaged gears.

crankshaft journals or cylinder walls.

(5) Inspect the gear pockets of the body. If you

find them scored or excessively worn, replace the

(12) You can now remove the assembled piston

pump.

(18), rings (20, 21, and 22), and connecting rod (15) by

(6) With the gears (12 and 15) and shafts (14

pushing piston assembly up through the top of the

and 16) position in the body, check for excessive play

cylinder block.

of the shafts and for contact of the gears with the pump

body. If you find these indications of wear, replace the

NOTE

pump.

Disassemble the pistons and piston rods

(7) Inspect all parts for cracks, distortion,

in sets, and keep the sets together. You

damaged threads, wear, and other damage; replace

must also be sure each piston and piston

damaged parts.

rod set is installed in the cylinder from

c. Reassembly and Installation.

which it was removed.

(1) Refer to figure 3-7 and reassemble the oil

pump. Check that the drive shaft turns easily without

(13) Refer to figure 3-11 (items 11 thru 22) and

binding when assembled.

disassemble the piston and connecting rod.

(2) Install the oil pump in the reverse order of

removal. To secure the pump firmly in place, aline the

b. Cleaning and Inspection.

locking setscrew (27, fig. 3-13) with the hole in the

(1) Discard and replace the piston rings.

pump body. After installing the setscrew, also install

(2) Clean all parts with cleaning solvent (fed.

the slotted head pipe plug (26). You may need to tap

the pump into position with a plastic hammer.

spec. P-D-680); dry thoroughly.

(3) Install the key (13, fig. 3-7) in the keyway of

(3) Inspect the pistons for wear, cracks, distor-

the drive shaft (14). Aline the keyway of the drive gear

tion, broken ring bands and distorted grooves, loose

(2) with the key (13) before securing the gear to the

piston pin-to-piston fit, and other damage; replace

shaft with the lock nut (1).

damaged pistons. Refer to table 3-1 for wear limits.

(4) Check the piston ring groove side clear-

3-15. Pistons and Connecting Rods

ance, using new piston rings. If side clearance exceeds

a. Removal and Disassembly. With the engine

the limits given in table 3-1, replace the piston.

mounted on an engine overhaul stand, proceed as fol-

lows:

NOTE

(1) Remove oil filter from flywheel shrouding

Pistons and bearings are individually

(para 3-4).

checked and fitted to the cylinders at

(2) Remove the flywheel assembly from the

reassembly. Before reassembly, the

engine (para 3-5).

cylinder bores must be checked as

(3) Remove the flywheel alternator (para 3-6).

directed in paragraph c (1) below.

(4) Remove the carburetor and manifolds

(TM 5-4320-272-12).

(5) Inspect the connecting rods for cracks, dis-

(5) Remove the air shrouding (para 3-7).

tortion, and other damage; replace damaged connect-

(6) Remove the governor assembly (para 3-9).

ing rods. Refer to table 3-1 for wear limits.

(7) Remove the gear cover (para 3-10).

(6) Inspect the bearing shells (14, fig. 3-11) for

(8) Remove the idler gear and shaft (para 3-

scoring, wear, cracks, and other damage; replace dam-

11).

aged bearings. When replacing the bearing shells, you

(9) Remove the oil pan (para 3-12), oil filler

must replace a complete bearing consisting of two

(para 3-13), and oil pump (para 3-14).

halves.

(10) To ream the ridge of the top of each cylin-

der bore you will need a standard ridge reamer. Blow

NOTE

metal fragments from the cylinder with compressed

New bearing shells are smooth and

air.

highly polished. After a few hours of

(11) Remove hexagon nuts (11, fig. 3-1 1). Tap

operation, the bearing surface becomes a

leaden grey and develops minute craters

the ends of the cap screws (12) with a plastic hammer

so that the surface has an almost cellular

to remove them. Take care not to mar the threads.

appearance. This is normal, and is not an

Remove the connecting rod bearing cap (13) and bear-

indication of impending bearing failure.

ing shell (14) from the connecting rod.

3-13