Crankshaft Main Bearings - Modifications
Group1
Number
8410
Model
928S
Part Identifier
1350
December 17, 1984
Subject:
Crankshaft Main Bearings
Various modifications have been made to crankshaft bearings and related engine parts. These changes have been introduced into production in steps.
A Thrust bearing 3 (1st modification)
B Thrust bearing 3 (2nd modification)
C Crankcase
Upper and lower section, assembling
Tightening procedures
D Crankshaft
E Main bearing, bottom 2, 4 and 5
F Main bearing 1
The following changes to the No. 3 thrust bearing, crankcase and crankshaft were made beginning with engine number:
81 E 00148 (manual trans.)
81 E 05344 (automatic trans.)
Thrust bearing 3 (modification 1)
The diameter of the axial bearing surfaces on thrust bearing 3, Part No. 928.101.141.00, was changed from 90 mm to 97 mm.
The new thrust bearing also made it necessary to change crankcase and crankshaft in the area of bearing No. 3
The diameter of the cut on bearing seat No. 3
in the upper and lower sections of the crankcase was changed from 93 mm to 100 mm.
Crankshaft
The diameter of lateral bearing surfaces at bearing No. 3 was changed from 90 mm to 97 mm.
The following additional changes were also made to the No. 3 thrust bearing, beginning with engine number:
81 E 00296 (manual trans.)
81 E 05718 (automatic trans.)
Thrust bearing 3 (modification 2)
The oil bores have been located further out and the width of the radial bearing surface was increased by 4 mm to 22 mm.
The total width of the thrust bearing, measured on the axial surface, was increased by 0.05 mm.
Main bearings 2, 4 and 5
Smooth bearing shells, Part No. 928.101.132.06, are installed in the lower section of the crankcase for main bearings 2, 4 and 5 (beginning with engine numbers listed above). These new bearing shells have only short oil groove shoulders and do not have oil bores.
The upper bearing shells, Part No. 928.101.132.03, have not been changed and remain with a continuous oil groove and oil bores.
Main bearing 1
The design of the No. 1 main bearing was changed to conform with the new lower bearing shells 2, 4 and 5 beginning with engine numbers:
81 E 00589 (manual trans.)
81 E 06817 (automatic trans.)
Spare Part Survey (standard size)
Note
The new thrust bearing 3, Part No. 928.101.142.01 (also 928.101.141.00), can only be used in conjunction with crankcases having a 100 mm dia. cut and crankshafts with 97 mm dia. bearing surfaces.
The new smooth bearing shells, Part No. 928.101.132.06, can be retrofitted to lower crankcase sections of all engines.
The bearing shells with an oil groove, part No. 928.101.132.03, must still be used in the upper sections of crankcases. This is also applicable for engines with a split main bearing no. 1. These engines require the use of four bearing shells for each bearing.
The new main bearing No. 1 can be retrofitted in all engines with a singlepiece bearing.
Crankcase upper and lower sections, assembling
Work sequence
- apply a thin coat of Loctite(R) 574 on lower section of crankcase
- mount lower crankcase section to upper
- screw on mounting nuts finger tight
- mount oil pump body and tighten both M8 bolts as follows:
Step 1 15 N-m (11 ft.lb.)
Step 2 20 N-m (14.5 ft.lb.)
Note
This will locate upper and lower sections of crankcase laterally.
- tighten mounting nuts to final torque in specified order as follows:
^ main bearing nuts, M12
1 to 10
Step 1 20 N-m (14.5 ft.lb.)
Step 2 40 N-m (29 ft.lb.)
Step 3 60 + 5 N-m (43.5 + 3.5 ft.lb.)
* Step 3 75 + 5 N-m (54 + 3.5 ft.lb.)
^ main bearing nuts, M10
11 to 22
Step 1 20 N-m (14.5 ft.lb.)
Step 2 40 + 5 N-m (29 + 3.5 ft.lb.)
* Step 2 50 + 5 N-m (36 + 3.5 ft.lb.)
* Crankcase with "X" next to case pair code and all crankcases with singlepiece main bearing No. 1:
Crankshaft Information
An additional centering pin for take-up of the flywheel is installed in the rear crankpin of crankshaft, Part No. 928.102.011.26.
The additional pin locates the flywheel with the crankshaft sensor gear ring on 1984 models.
If this crankshaft is to be installed in engines prior to the 1984 models, the centering pin must first be removed as the flywheel will not have a corresponding centering bore.