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 TM 55-1905-219-14-5
3-97. CRANKSHAFT.
The crankshaft maintenance instructions are as follows:
DESCRIPTION
PARAGRAPH
Crankshaft Bearings
Crankshaft
Crankshaft Seals
3-97.1. CRANKSHAFT BEARINGS.
a. The crankshaft main bearings shells are precision made 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.
g. Bearing failures may result from deterioration (acid formation) or contamination of
the oil or loss of oil. An analysis of the lubricating oil may be required to determine if
corrosive acid and sulphur are present which cause acid etching, flaking-and pitting.
Bearing seizure may be due to low oil or no oil.
3-1710
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