HT4100 MAIN BEARING USAGE UPDATED REVISIONS LISTED

MODELS AFFECTED: ALL WITH HT4100 ENGINES

With the introduction of the 1987 model year, minor revisions have been incorporated in the HT4100 main bearings which dictated the following revisions to the bearing usage chart from page 3 of Serviceman Bulletin T-84-5C.

Service Bearing Edge Part Part Application Position Color Number* Number** Status

Original Production #1 None 18006622 18009086 Obsoleted by 18012316 2nd Design Production #1 Purple 18012275 18012316 Obsoleted by 18014329 3rd Design Production #1 Red 18014079 18014329 Service Only O.S. #1 Blue 18012276 18012317 Obsoleted by 18014307 (2nd Design) Service Only O.S. #1 Blue 18014306 18014307 (3rd Design) Original Production #2 None 18006622 18009086 Obsoleted by 18013442 2nd Design Production #2 None 18013016 18013442 Original Production #3 None None 18009088 Obsoleted by 3634715 (2nd Design Production (#3) (None) (1640033)(3634715) 1987 1/2) Original Production #5 None None 18009087 Obsoleted by 18013793 2nd Design Production #5 Pink None 18013793 (Use In Longitudinal Engines Only) Service Only O.S. #5 Blue None 18012878 (Use In Longitudinal (2nd Design) Engines Only) (3rd Design (#5) (Green)(19013607)(18013789) (Use In Transverse Production 1987) Engines Only) (Service Only O.S. (#5) (Black)(18013608)(18013790) (Use In Transverse 3rd Design) Engines Only) (Updated information in parentheses )

* Part number is number stamped on back of bearing shell. Use this number for identification.

** Service number is number GMSPO (GM Service Parts Operations) assigns to part and prints on box. Use this number for ordering parts.

Main Bearing #3 (Thrust Main) -----------------------------

While no significant revisions have been incorporated in this bearing, a new supplier has been selected which has necessitated a new part number. This change is scheduled to occur sometime during the 1987 model year, however, establishing a breakpoint is not required since both parts can be used interchangeably.

Main Bearing #5 ---------------

A revised #5 main bearing entered production at the start-of-production 1987. This 3rd design bearing can be identified by a green edge color and lack of a 2nd oil groove at the edge of the bearing facing the rear main seal. The purpose of this 2nd groove is to channel oil away from the rear main seal. Research at Cadillac has shown that the one piece rear main seal on transverse HT4100 engines does not require this feature. The 2nd design parts should be used on longitudinal engines and the newer 3rd design parts restricted to transverse applications only. The GMSPO parts catalog will be revised to reflect these changes.

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.