Engine - Knocking Noise When Cold
90bmw21 Group 11 EngineBulletin Number 11 12 90 (3154)
Woodcliff Lake, NJ November 1990 Service Engineering
SUBJECT: Piston Replacement
ENGINE: M30 (B35)
Situation: Isolated reports have indicated that a knocking noise may be heard from the engine during the first 2-5 minutes of operation when cold. The noise is most noticeable when the engine is under a load.
Due to unfavorable manufacturing tolerances in conjunction with country-related operating conditions, pistons produced by Nueral/Alcan should not be used on 3.5 liter engines when piston replacement becomes necessary.
Correction: Whenever the above complaint is received all possible basics should be checked, i.e., valve adjustment, fuel quality, etc., before considering a piston replacement. If no external engine faults are found, further internal engine checks should be carried out to determine the piston manufacturer. If Nueral/Alcan pistons are installed, they should be replaced with six new Mahle pistons.
Note: New pistons and wrist pins come as a matched set.
Only install pistons of the same make and weight class. The manufacturer and weight class are stamped in the piston crown.
Parts
Information: Nueral/Alcan pistons have been frozen in the PDCS. The new Mahle piston part numbers are:
Part number Nominal size
11 25 1 717 137 92.000 mm ("0")
11 25 1 717 138 92.080 mm ("00")
11 25 1 717 139 92.250 mm (+0.25)
11 25 1 717 140 92.500 mm (+0.50)
All Nueral/Alcan piston part numbers have been superseded to the above listed Mahle piston part numbers.
Warranty
Information: Covered under the terms of the applicable BMW New Car Limited Warranty.
Defect code: 11 25 00 41 00
Labor operation: 11 25 000
Labor allowance: as applicable
For quality and product observation reasons please contact your District Service Manager before conducting the piston replacement.