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 TM 55-1905-221-14-3
6-28. CRANKSHAFT AND MAIN BEARINGS.
The maintenance instructions for the crankshaft and the main bearings are contained in the following paragraphs:
DESCRIPTION
PARAGRAPH
Crankshaft Bearings
Crankshaft
Crankshaft Seals
Crankshaft Timing Gear
3-32.1 CRANKSHAFT BEARINGS - MAINTENANCE INSTRUCTIONS.
a. The crankshaft main bearings shells are precision make and are replaceable without machining. They consist of
an upper bearing shell seated in each cylinder block main bearing support and a lower bearing shell seated in each main
bearing cap. The bearing shells are prevented from endwise or radial movement by a tang at the parting line at one end
of each bearing shell. The tangs on the lower bearing shells are off-center and the tangs on the upper bearing shells are
centered to aid correct installation.
b. The bearing caps are numbered 1, 2, 3, etc., indicating their respective positions and when removed, must
always be reinstalled in their original position.
c
An oil hole in the groove of each upper bearing shell, midway between the parting lines, registers with a vertical
oil passage in the cylinder block. Lubricating oil, under pressure, passes from the cylinder block oil gallery by way of the
bearing shells to the drilled passages in the crankshaft, then to the connecting rods and connecting rod bearings.
d. The lower main bearing shells have no oil grooves; therefore, the upper and lower bearing shells must not be
interchanged.
e. Thrust washers on each side of the rear main bearing, absorb the crankshaft thrust. The lower halves of the two-
piece washers are doweled to the bearing cap; the upper halves are not doweled.
f. Main bearing trouble is ordinarily indicated by low or no oil pressure. All of the main bearing load is carried on the
lower bearings; therefore, wear will occur on the lower bearing shells first. The condition of the lower bearing shells may
be observed by removing the main bearing caps.
6-484
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