Changed or Adapted Components

Furthermore, the following components have been changed or adapted on the new M5:


The S38 B36 employs the 1.2 Motronic, utilizing a hot-wire air mass sensor and an idle control valve. Basically, the system is similar to the one used on the M70 engine. It is fully adaptive and requires no maintenance or adjustments.


The pistons were modified as follows:

To compensate for the greater stroke, the compression distance (i.e. distance between wrist pin bore and piston top) was decreased. The width of the third (oil) ring was reduced to 2.5 mm; the piston bowl depth is now 3.35 mm.


The cast aluminum oil pan contains an oil deflector to collect the oil and divert it into the sump to improve overall mechanical efficiency and reduce oil foaming.


A double roller chain is used to drive the camshaft. To ensure operation at a low noise level and reduce oscillations, the chain tensioner rail and guides have been refined.

The oil filter housing is conveniently accessible from the top to provide the same easy serviceability as on the M30 engine.



The thermostat housing has been redesigned; it contains an annular slide valve which is actuated by a temperature-dependent expansion element containing wax.

Please note its proper position when reinstalling this element.


Note: The cooling system has been modified to match the increased engine power. A newly designed coolant reservoir requires a special filling/bleeding procedure. (Please refer to S.I. 17 01 90 (3037) and the Owner's Manual.)
The six separate intake runners have been increased in diameter and two additional vacuum connectors have been added to the respective pipes of the 5th and 6th cylinders. There is no idle adjustment screw since the system is maintenance-free.


For instructions on how to synchronize the separate throttles in case of an engine repair, please refer to the "Repair Manual" or microfiche "Repair Instructions for Construction Groups No. 9".

As part of the PDI (as well as with every engine washing), the bearings, balls and sockets of the entire throttle linkage assembly have to be lubricated with Molykote Long Term Grease.


In order to optimize the torque characteristics in the speed range between 4,120 RPM and 6,720 RPM, a new dual chamber ram air induction system has been developed. The six separate pipes connecting the plenum and the intake runners are made of plastic. They are attached to the plenum by rubber sleeves to eliminate vibration-induced noise and ensure a tight fit under all operating conditions.



A new oil separator is mounted underneath the plenum. It collects the blow-by vapors from the valve cover, separates the oil, and drains it into the sump.
The engine block, which is derived from the M30 crankcase, has an additional flange (in the area where the dipstick tube is attached), to accept the drained oil from the oil separator.


The new, forged steel crankshaft has 12 balancing weights; due to a weight reduction of the crankwebs, the balancing weights could also be reduced in weight. In addition, their design was streamlined to reduce frictional losses.


A torsional vibration damper bolts into the front of the crankshaft. It, too, has been reduced in weight and the circumferential reference (exciter) wheel has been revised for the higher maximum engine speed.


Installation Note: Use special tools 112240 and 113230 to tighten the center bolt.



The exhaust manifold is made of special steel and is equipped with air injection connectors and 6 separate connectors for a CO probe.


Installation Note: The special tool 116070 is used to loosen and tighten the exhaust flange nuts.
The camshafts were redesigned to improve volumetric efficiency.

The lift curve area was increased by higher cam lift (10.7 mm) and longer duration (264/110). The S38 B36 engine also uses redesigned camshaft sprockets.


The inverted bucket tappets were increased in diameter to 37.5 mm, the adjustment shims to 33 mm.

Both the inner and outer valve springs were modified to accommodate changes in the valve train and ensure positive closing of the valves up to the new redline of 7,250 RPM.


The connecting rods are the same as on the "old" S38 engine; the distance between the axes of the big end and small end bores is 144 mm.