1.3.4 Main Bearings
DETROIT DIESEL 53
The lower main bearing shells have no oil grooves; therefore, the upper and lower bearing shells must not be
interchanged.
Thrust washers (Fig. 1) 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.
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 main bearing shells may
be observed by removing the main bearing caps.
If main bearing trouble is suspected, remove the oil pan, then remove the main bearing caps, one at a time, as outlined
below and examine the bearing shells.
Fig. 4 - Removing Upper Main Bearing Shell
(Except Rear Main)
Fig. 5 - Removing Upper Rear Main Bearing Shell
Remove Main Bearing Shells (Crankshaft in Place)
The bearing caps are numbered 1, 2, 3, etc., indicating their respective positions and, when removed, must always be
reinstalled in their original position.
All crankshaft main bearing journals, except the rear journal, are drilled for an oil passage. Therefore, the procedure for
removing the upper bearing shells with the crankshaft in place is somewhat different on the drilled journals than on the
rear journal.
Remove the main bearing shells as follows:
1.
Drain and remove the oil pan to expose the main bearing caps.
2.
Remove the oil pump and the oil inlet pipe and screen assembly.
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