1.3.6 Cylinder head
A three cylinder engine has one cylinder head.There is one cylinder head in four cylinder engine. A six
cylinder engine has two cylinder heads. The 98 engine has two cylinder heads: one for three cylinders
(front) and one for four cylinders (rear). Every cylinder has four valves and in the middle of the valves there
is a place for the injector. The injector is located vertically in the centre of the cylinder and in the middle of
the combustion chamber. This ensures accurate and homogenous mixing of fuel and air and leads to clean
and low emission combustion with good efficiency.
Each cylinder has its own inlet and exhaust ports located on either side of the head. Every inlet valve has
its own inlet port but there is only one exhaust port for every two of the cylinder’s exhaust valves. There
are no water holes on the inlet side of the cylinder head. This eliminates the possibility of water entering
the inlet air.
Cylinder head bolts are high tensile bolts, which are tightened up to yield limit using the angle tightening
method. Due to the large stretch, the tightening forces are kept constant during the whole lifetime and
retightening is unnecessary.
The injector and its side feeding pipe locations are machined directly into the cylinder head. The port for
the side feeding pipe is located between the inlet ports. The inlet and exhaust valve guides are identical
and can be interchanged. Inlet and exhaust valves are fitted with separate valve seat rings.
1.3.7 Crank mechanism
The crankshaft is forged from chrome alloy special steel and is induction hardened at the bearing and
sealing surfaces. This makes it possible to grind bearings four times and 98 engine two times without a
new heat treatment. Gear wheels are located at the front end of the crankshaft. They are a press fit, and
drive the idler wheel and oil pump. The belt pulley/vibration damper is fastened to the crankshaft with a
cone joint. An oil deflector ring is fitted between the hub and gear wheel. The 98-engine has larger cone
and an additional seal ring.
The crankshaft is supported on the cylinder block by main bearings, which are placed on both sides of each
cylinder. There is therefore one main bearing more than there are cylinders. The crankshaft thrust washers
are placed in both sides of the rearmost main bearing.
A flywheel, on which there is a press-fit starter ring gear, is fitted at the rear end of the crankshaft. The
forged connecting rod has an I-cross-section. The bearing location at the bottom end of the connecting rod
is fracture-split, and the bearing cup is secured by two special elongated screws. The upper part has a
wedge-shaped bearing location, in which the piston pin bearing bushing is fitted with a press fit.
The piston is made of a eutectic aluminium alloy. In the upper face of the piston there is a combustion
chamber. The shape of the chamber is intended to maximise the mixture of air and fuel. The upper ring
location is formed in a cast iron ring, which is cast in the piston. In addition, the piston is graphite-coated to
ensure correct running-in.
The piston has three rings. The upper molybdenum-coated ring has a wedge-shaped cross-section. The
middle ring is tapered and it fits into its groove. The taper takes up the clearance. The oil control ring is
spring-loaded and it has a two-stage, chromed scraping edge.
Four-cylinder engines are equipped with a balancer unit. The eccentric weights, which rotate at twice the
engine speed, even out the vibration forces exerted by the movement of the pistons and the crank
mechanism.
1. Introduction
1-14 4th Generation Engines
8370 79492
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