1.3 MULTIJET 16V
(75 & 90 HP)
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3.2.4 CYLINDER HEAD
The cylinder head is of the single-structure type and is made from aluminium and silicium
alloy.
Two overhead camshafts, made of ductile cast iron, are housed within an overhead; the drive
is of the combined chain-gear type.
The four valves per cylinder (parallel and vertical) are located in their respective guides and
driven by rocker arms actuated by the cams of the cam axles and kept into contact with the
valves by means of hydraulic tappets.
The valve guides are driven into the respective cylinder head housings by interference. The
inner diameter is optimized, after assembling, by means of a special boring machine.
Compared with the cylinder heads with precombustion chamber, the entire combustion
process takes place in the combustion chamber obtained on the piston.
The gasket between the cylinder head and the engine base is made of metal; moreover, the
cylinder head shall not be retightened during the entire engine life.
On the versions fitted with the 90 HP engine, the combustion system has been necessarily
modified in order to improve the input and output flows.
The inlet duct design has been modified by increasing the flow capacity; at the same time,
volumetric efficiency at high speeds has been improved, following a reduction of the swirl
level.
The combustion chamber design has been modified, by increasing the chamber diameter and,
as a result, reducing the compression ratio from 18:1 to 17.6:1.
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