Engine - Revised Specs Cylinder Head Bolts/Piston
REF. NO. 01/22bTO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: May 1992
Revision:
Reference to engine 601.91 (non USA engine) removed from sections C and D
SUBJECT:
A. ENGINES 602.96, 603.96, 603.97
CYLINDER HEAD BOLTS WITH INCREASED TENSILE STRENGTH
B. ENGINES 601, 602, 603
REVISED TORQUING PROCEDURE FOR CYLINDER HEAD BOLTS
C. ENGINES 602.91
PISTONS WITH GRAPHITE-TREATED PISTON SKIRTS
0. ENGINES 602.91
CYLINDER HEAD BOLTS WITH INCREASED TENSILE STRENGTH
E. ENGINES 601, 602, 603
REVISED MAXIMUM LENGTH OF CYLINDER HEAD BOLTS
A. Engines 602.96, 603.96, 603.97
Cylinder Head Bolts with Increased Tensile Strength
To allow an increased torque preload on the cylinder head bolts, modified cylinder head bolts with increased tensile strength entered production as of the engine end numbers listed in the table.
When performing a R&R of the cylinder head on any 602.96, 603.96, 603.97 turbodiesel engine, the previous version cylinder head bolts must be replaced with the modified version.
The modified cylinder head bolt has a larger bolt head surface and increased tensile strength.
Identification
The modified bolt can be identified by the code number and ribs on the head.
Previous Version (A, Figure 1
Bolt head diameter 20.7 +/- 0.3 mm
Code number 85 or 850
Modified version (B, Figure 1)
Bolt head diameter 21.2 +/- 0.3 mm
Code number 95 or 950
Two ribs on bolt head (arrows, Figure 2).
Parts Information
B. Engines 601, 602, 603
Revised Torquing Procedure for Cylinder Head Bolts
A modified torquing procedure for the (M10) cylinder head bolt is valid for these engines, effective immediately.
The revised procedure allows the maximum clamping force to be applied to set the head gasket.
Note:
As always, it is extremely important to observe the cylinder head bolt tightening sequence (see microfiche job no. 01-415).
Torquing procedure
M8 cylinder head bolts are still to be torqued to 25 Nm.
C. Engines 602.91
Pistons with graphite-treated piston skirts
Pistons with graphite-treated skirts have replaced the previous pistons with lead-coated skirts. Piston code no.: 22
Note:
The graphite-treated pistons can also be installed in older engines. Only the new piston will be available as a spare part.
Parts Information
Part Name Part Number
Piston 601 030 22 17
D. Engines 602.91
Cylinder Head Bolts with Increased Tensile Strength
Starting 06/91 production, the naturally aspirated engines have higher tensile strength head bolts as the turbo engines have had since 05/90.
Note:
The new head bolts can also be installed on engines which have already been in operation. If one cylinder head bolt needs to be replaced on an engine with the old style head bolts. always replace all the head bolts. Remaining supplies of the old style head bolts can be used up on engines built prior to the phase-in of the revised head bolt. Only the new head bolt will be available as a spare part.
E. Engines 601, 602, 603
Revised maximum length of cylinder head bolts
Always check length (L, Fig. 3) of cylinder head bolts before reuse. If head bolt length exceeds maximum dimension, use new cylinder head bolts.
Dimensions of cylinder head bolts