Technical data

19
9
The specified tightening operation for the
connecting rod bolts must be adhered to
precisely. Tightening the bolts three times to
the same tightening angle gives rise to a
certain training effect (work hardening) in the
connecting rod bolts, resulting in increased
pretensioning force and simultaneously in
pretensioning force spread. Disregard of or a
mix-up in the bolt tightening instructions can
lead to 100 % engine damage by connecting
rod bolts working loose.
Pistons
The piston is cast from aluminium
(Al Si12CuNiMg). Since an aluminium piston
is an unfavourable friction partner for an
aluminium cylinder, the piston skirt is coated
with a galvanic ferrous layer (Ferrostan) at a
layer thickness of approx. 10 µm. An additional
approx. 2 µm tin layer serves as a running-in
layer.
Camshaft
The camshaft mounted in nine bearings is a
hollow chill casting (GGG 60). For the first
time, the wheel for the camshaft sensor is cast
on the camshaft on the S85. An M12x1 thread
is integrated in the camshafts for the central
screw connection of the VANOS gear
mechanism.
Valve springs
Conical valve springs are used on the S85.
The same springs are used for the intake and
exhaust.
Valve cotters
The valve cotters are designed as single-row
clamping-type cone cotters. In contrast to the
three-row valve cotters, these clamping-type
cone cotters prevent the valve turning during
operation as neither a cleaning effect nor
running-in is necessary thanks to the clean
and efficient combustion and the very close
production tolerances. An advantage of the
clamping-type cone cotters is their low weight
(approx. 50 % lighter than the three-row valve
cotters).
In addition, the force of the valve spring is not
transmitted positively but rather non-positively
via the grooves in the valve stem. At a stem
diameter of 5 mm, this arrangement protects
the material more effectively.
3 - Installation direction of connecting rod