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Bearing Knock On
Chrysler Products Engines with Air Conditioning
Chrysler, Dodge and Plymouth vehicles equipped with air conditioning may develop a slight bearing knock due to the additional load placed on the front crankshaft main bearing by the drive belts.
The noise is most pronounced at idle, or slightly above idle, with the transmission in gear. The intensity can be increased or decreased by tightening or loosening the drive belts. This noise will not cause a bearing failure. However, should it be necessary to reduce the noise to satisfy a complaint, the condition can be minimized by select fitting of the No. 1 main bearing. Bearing clearance may be checked with plastigage (range .001 to .003) following the instructions included in the plastigage package.
CAUTION: Plastigage readings are only accurate within the .001 - .003 range specified.
(Insert Illustrations)
To avoid the noise associated with high belt loads, the No. 1 main bearing clearance should be .001 to .0015. The clearance can be checked with plastigage in the lower shell if the drive belts remain tight. (Plastigage instructions mention the weight of the crank will give an erroneous reading if the crank is not supported.)
Fitting The Main Bearing With Plastigage
If the No. 1 main bearing clearance is:
1. Over .0015: Replace with new standard upper and lower shells. (Loosen the drive belts to roll out the upper bearing shell.)
2. With new shells; still over .0015 but less than .0018: Install one .001 undersize shell (upper or lower) and recheck clearance.
3. Over .0018 but less than .0025: Install .001 undersize upper and lower shells and recheck.
The AERA Technical Committee
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