BEARING INSPECTION AND INSTALLATION

TM 10-3930-644-14&P

journals for out-of-round and tapered condition. The limit

Some models use tri-metal bearings which, when

is .0005".

new, are smooth and highly polished. However, a

very few hours of operation will change their

If the crankshaft is scored, or worn enough so that new

appearance completely.

The bearing surface

bearings will not fit with the required clearance, the

becomes a leaden gray 'n color and develops minute

crankshaft should be reground.

craters, almost cellular in appearance (Figure 6-5)

which follow the pattern of the matrix.

This

Standard crankshafts may be reground to decrease the

appearance is a natural characteristic of this type

diameter a maximum of .040". When reground, the fillet

bearing and in no way indicates failure.

radii must be within dimensional limits and must be

perfectly blended into thrust and bearing surfaces

Refer to Figures 6-6 and 6-7 for the appearance of

(Figure 6-4).

corrosion and scoring damage to bearings.

D. BEARING INSPECTION AND INSTALLATION

1. General

Both the connecting rod and main bearings are o" the

steel-backed, precision type.

Due to the close

machining of this type of bearing, no fitting, filing,

scraping, boring or other adjustment is required or

permissible.

Replacement must be in complete

bearing units. Never replace only one-half of a

bearing. Service bearings are available in .010",

.020", and .040" undersize for use on reground

crankshafts. Never attempt to adjust a bearing by

filing, grinding, or lapping the bearing cap. The

bearing seats are precision ground with the caps in

place. Any metal removed from either side prevents

Figure 6-6. Bearing Damage Due to Corrosion

the proper fit of a connecting rod bearing in the rod,

and in the case of a crankcase, makes the entire

crankcase unsuited for further use.

2. Bearing Inspection

NOTE

Inspect the bearing shells and

crankshaft journals. If there is any

indication of distortion, scoring or

actual wear, the bearing shells must

be replaced.

Figure 6-7. Scored Bearing Due to Dirt of Lack of

Lubrication

If the visual inspection appears satisfactory, bearings

should be removed and checked for thickness using a

ball micrometer.

To remove the upper half of the bearing shell use a

special tool obtainable at

Figure 6-5. Appearance of a Good Bearing.

R-104-1

3-18