26
Design and Function
Component specification
Cylinder block
The cylinder block is made of special alloy cast iron
and cast in one piece. Combustion induced tensile
stresses in the cylinder head screws are directed
through stiffened sections between the cylinder
block walls into the main bearings.
The camshaft bearings are bored to the correct di-
mension and aligned after installation.
Cylinder heads
The engine has a whole cylinder head. The cylinder
head surface is absolutely flat and therefore the
combustion chamber is completely extended to the
piston head. The seal between the engine block and
cylinder head is of the composite type. The cylinder
head is secured with 27 screws (31/32-series 19
screws). The screws are tightened by torque tighten-
ing in three stages with complementary protractor
tightening in two stages.
Pistons
The pistons are made of an aluminum alloy. The up-
per compression ring, which leads off the greater
part of the heat transferred by the piston rings, is
located in a forged piston ring carrier of high alloy
cast iron. This gives the piston ring groove long
service life despite the heat stresses. The piston
ring grooves for other piston rings are machined di-
rectly into the piston.
All engines have piston cooling. The pistons have a
channel inside the upper section of the pistons
through which the oil for piston cooling passes. The
intake is in the inner mantle by the piston bolt hole,
the drainage hole is in the upper section of the pis-
ton under the combustion chamber. The piston cool-
ing oil is sprayed from fixed nozzles, one for each
cylinder. Oil is sprayed from the nozzles up to the
piston cooling channel. The oil to the piston cooling
is allowed forward from a pressure valve which
opens when the oil pressure has reached 2.2–3
kp/cm
2
.
By piston cooling the temperature is reduced
by approximately 20°C measured at the upper piston
ring groove.
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