Main Bearing Bolt Hole - Revised
Number: 83-I-54Section: VI
Date: April, 1983
Subject: MAIN BEARING BOLT HOLES 1983 V6 DIESEL ENGINE (VIN CODES "T" AND "V")
TO: ALL CHEVROLET DEALERS
Main bearing bolt hole thread pitch for number 2 and 3 main bearings have been changed from 1.75 mm to 1.76 mm on V6 diesel engines. The main bearing bolt has not changed. This results in an interference fit with the last few threads when the bolt is screwed into the hole. This interference spreads the load throughout the bulkhead rather than concentrating it at the surface. blocks that have a main bearing bolt hole pitch of 1.76 mm for number 2 and 3 main bearings are identified by a stamped letter "G" behind the cast part number. The cast part number is located on the top rear of the block next to the oil pump drive assembly. When installing these bolts it is essential that engine oil be applied to the threads to prevent galling. It is normal for the bolt to tighten up slightly during the last few turns upon installation. Do not attempt to "clean up" number 2 and 3 main bearings block threads by retapping with standard tap size M12-1.75. The M12-1.76 tap used is not a standard tap size.