Engine - Connecting Rod/Piston Weight Classifications
Group 11Engine
Bulletin Number
11 02 94 (3960)
Woodcliff Lake, NJ
April 1994
Product Engineering
This Service Information bulletin supersedes S.I. 11 29 82 (688) dated August 1983 which should be removed from your S.I. binder and discarded.
SUBJECT:
Connecting Rod and Piston Weight Classifications
MODELS:
All with M2O and M3O Engines
Situation:
The weight classification of replacement connecting rods which is stamped on the bottom of the bearing cap, i.e., A1-A9 or B1-139, is no longer used to match the weight of a single replacement connecting rod to the existing connecting rods of an engine. Replacement connecting rods which are ordered from the BMW Parts Distribution Centers all cover the entire range of weight tolerances and may be used together with any other weight class connecting rods regardless of the weight class stampings on the bottom of the bearing cap.
The weight classification of replacement pistons which is stamped in the piston crown, i.e. "+" or "-", is no longer used to match the weight of a single piston to the existing pistons of an engine if the replacement of individual pistons becomes necessary. Replacement pistons which are ordered from Parts all cover the entire range of weight tolerances and may be used together with other weight class pistons during repairs.
Notes:
^ When replacing piston(s), only install pistons of the same make.
^ Pistons and wrist pins are matched and should not be mixed up during repairs.
Warranty Status:
Information only.