DIESEL ENGINE SERVICE INFO. MISC. PARTS AND SERVICE

A. Main Bearing Bolt Holes - V6 Diesel (VIN Codes "T & "V")

Main bearing bolt hole thread pitch for number 2 and 3 main bearings has been changed from 1.75 mm. to 1.76 mm. on V-6 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. Engine 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 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 slightly during the last few turns upon installation. Do not attempt to "clean up" 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.

B. Diesel Injection Pump Repair Parts

Diesel engine injection pump repair parts are now available thru WDDGM. Repair parts available are listed in the current parts catalog groups 3.300 thru 3.340.

C. Engine Miss and Exhaust Smoke at Highway Speeds - V6 Diesel (VIN Codes "T" & "V")

An engine miss followed by a puff of blue smoke out the exhaust may be caused by engine oil leaking into the intake area of the cylinder head. The pipe-thread plugs that cover the upper Torx head bolts may be the source of an oil leak if not fully seated.

D. Diesel Engine Drive Belts 1980-1983 V-8 Diesel

A crankshaft pulley torque compensator, similar to that used on the V-6 diesel engine is now being used on the V-8 diesel engine. The torque compensator reduces the torque variations being transmitted to the drive belt and will increase drive belt life.

The torque compensator is available for 1980 through 1983 V-8 diesel models, with A/C, that use a two groove crankshaft pulley. The torque compensator, and four belts required for installation are available through WDDGM. Part number is 22521773.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.