BMW 3 (E46). Manual — part 29
Cylinder block and crankshaft
The cylinder block is cast aluminum
alloy (AlSi9Cu3) with cast iron cylinder
liners. The cylinders are exposed on all
sides to circulating coolant.
The counterweighted crankshaft rotates
in replaceable split-shell main bearings.
Oilways drilled into the crankshaft
provide bearing lubrication. Oil seals
pressed into alloy seal housings are
installed at both ends of the crankshaft.
The 2.5 liter crankshaft is cast iron. The
2.8 and 3.0 liter engines use a forged
steel crankshaft to accommodate the
higher torque. The crankshaft for the 3.0
liter engine is adapted from the S52 M3
engine.
Connecting rods and pistons
The forged steel connecting rods use
replaceable split-shell bearings at the
crankshaft end and solid bushings at the
piston pin end.
The pistons are of the three-ring type
with two upper compression rings and a
lower one-piece oil scraper ring.
Full-floating piston pins are retained with
circlips.
The 2.8 and 3.0 liter engines use a
graphite coating on the piston skirts to
reduce friction and noise.
Cylinder head and valvetrain
Cooling passages in the cylinder head
are designed for optimum coolant
circulation, allowing the head to operate
at lower temperatures than the cylinder
block.
The aluminum cylinder head uses chain-
driven double overhead camshafts and
four valves per cylinder. The cylinder
head employs a crossflow design for
greater power and efficiency. Intake air
enters the combustion chamber from
one side while exhaust gasses exit from
the other.
Oilways in the head provide lubrication
for the camshafts and valvetrain.
Valve clearance is set by self-adjusting
(zero-lash) hydraulic lifters for reduced
valve noise and the elimination of routine
valve adjustment.
Exhaust manifolds
Each exhaust manifold assembly
incorporates a catalytic converter. The
converters are mounted close to the
engine for faster heat up. Pre- and
post-catalyst oxygen sensors are a
mounted in each exhaust manifold.
Cooling system
The cooling system circulation is
designed so that coolant flows directly
from the coolant pump to the cylinder
head. The coolant is fed from the coolant
pump through a cast coolant feed
passage to the rear of the cylinder head.
From there it flows forward to the
thermostat housing, radiator and heater
valve.
The coolant passages in the cylinder
block are only connected to the coolant
supply through the holes in the head
gasket. A reduced volume of the coolant
flows through the cylinder block.
All models are equipped with a
DME-controlled electric cooling fan. On
some models, a supplemental cooling
fan is used. See
170 Radiator and
Cooling System
for specific configuration
and application information.
An electrically heated thermostat
controls the flow of coolant through the
radiator based on coolant and outside
temperature, engine load, and driving
speed, rather than just coolant
temperature.
The DME-controlled heated thermostat
allows the engine to be operated at
higher controlled temperatures during
low and part throttle. This optimizes
operating temperatures in both cylinder
head and block, reduces friction and
thereby fuel consumption.
The cooling system is designed to:
Reduce operating temperatures of
cylinder head. The result of lower
temperatures is increased torque
due to improved volumetric
efficiency.
Increase operating temperature of
cylinder block.
Lubrication system
The lubrication system is pressurized
whenever the engine is running. The oil
pump draws oil through a pickup in the
bottom of the oil pan, then forces it
through a replaceable oil filter and into
the engine oil passages.
The chain-driven oil pump is bolted to
the bottom of the cylinder block inside
the oil pan. A pressure relief valve limits
the maximum system pressure. A
bypass valve prevents the oil filter from
bursting and insures engine lubrication
should the filter become plugged. See
119 Lubrication System
for additional
information.
Resonance/turbulence intake
system
The intake manifold, made of molded
plastic, is configured as two sets of three
runners. This design enhances low end
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