DETROIT DIESEL 53
Main Bearings 1.3.4
Fig. 6 - Comparison of Main Bearing Shells
3. Remove one main bearing cap at a time and inspect the bearing shells as outlined under Inspection. Reinstall each
bearing shell and bearing cap before removing another bearing cap.
a.
To remove all except the rear main bearing shell, insert a 1/4" x 3/4" bolt with a 1/2" diameter and 1/16" thick
head (made from a standard bolt) into the crankshaft journal oil hole. Then revolve the shaft to the right
(clockwise) and roll the bearing shell out of position as shown in Fig. 4. The head of the bolt must not extend
beyond the outside diameter of the bearing shell.
b.
Remove the rear main bearing upper shell by tapping on the edge of the bearing with a small curved rod,
revolving the crankshaft at the same time to roll the bearing shell out as shown in Fig. 5.
c.
The lower halves of the crankshaft thrust washers will be removed along with the rear main bearing cap. The
upper halves of the washers can be removed for inspection by pushing on the ends of the washers with a small
rod, forcing them around and out of the main bearing support.
Inspection
Bearing failures may result from deterioration (acid formation) or contamination of 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.
Check the oil filter elements and replace them if necessary. Also check the oil by-pass valve to make sure it is operating
freely.
After removal, clean the bearings and inspect them for scoring, pitting, flaking, etching, loss of babbitt or signs of
overheating (Fig. 6). The lower bearing shells, which carry the load, will normally show signs of distress before the upper
bearing shells.
Inspect the backs of the bearing shells for bright spots which indicate they have been moving in the bearing caps or
bearing supports. If such spots are present, discard the bearing shells.
Measure the thickness of the bearing shells at point "C", 90from the parting line, as shown in Figs. 7 and 8. Tool J 4757,
placed between the bearing shell and a micrometer, will give an accurate measurement.
April, 1974
SEC. 1.3.4
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