Construction
0---15
40--- 5
Cylinder head
645---engines have two cylinder heads which are exchange-
able with each other. Each cylinder has its own inlet and
exhaust ports located on either side of the head. Between hot
exhaust valves a cool inlet valve is fitted to balance the ther-
mal load.
Cylinder head bolts are high tensile bolts which are tightened
up to yield limit using angle tightening principle. Due to the
large stretch the tightening forces are kept constant during
the whole lifetime and retightening is unnecessary.
The injector locations are machined directly into the cylinder
head. The inlet and exhaust valve guides are identical and
can be interchanged. In addition, the inlet and exhaust valves
are equipped with replaceable valve seat inserts.
Valve mechanism
The valve mechanism is operated by the camshaft which is
located in the cylinder block. The drive is transferred with the
help of tappets and pushrods. The camshaft gear wheel is
fitted with a press fit and fixed with a key. Each bearing is lubri-
cated by the force feed lubrication system through drilled oil-
ways in the motor block.
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 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. In addition, the front end of the crank-
shaft has splines for the hub of the ribbed V---belt pulley. An
oil deflector ring is fitted between the hub and gear wheel.
The crankshaft is supported on the cylinder block by main
bearings which are placed on both sides of each cylinder.
Thus there is one main bearing more than cylinders. The
crankshaft thrust washers are placed in both sides of the rear-
most main bearing.
At the rear end of the crankshaft there is fitted a flywheel on
which is a press---fit a starter ring gear. The forged connecting
rod has an
I
---section cross---section. The bearing location at
the bottom end of the connecting rod is angle split, and the
bearing cup is secured by two special elongated bolts. 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 an 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 piston has three rings. The upper molyb-
denum---coated ring has a wedge---shaped cross---section.
The middle ring is tapered and it fits into its groove. The taper
taking up the clearance. The oil control ring is spring loaded
and it has a two---stage, chromed scraping edge.
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.
Содержание 645 Series
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