Page 146 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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130 Automobile mechanical and electrical systems

Figure 2.97 V6 cylinder head with two cams in position. (Source: GM Media)

Figure 2.98 Cam profi les: 1, pointed cam; 2, cam with steep profi le; 3, trailing face; 4, leading face

improved signifi cantly via a temperature reduction of up to 100°C. These valves
are also known as bimetal type. Note that a sodium-fi lled valve of this type must
be handled with care as sodium exposed to air is fl ammable and will self-ignite.

2.1.3.6 Camshaft
Key fact
The camshaft, on most modern engines, is mounted in bearings formed into
The camshaft has cam lobes for
the cylinder head via an in-line boring process ( Fig. 2.97 ). The camshaft is
each valve. To ensure the correct
forged from steel or cast iron and the bearings and cam surfaces are a smooth,
sequence of valve timing, the
machined fi nish. The camshaft has cam lobes for each valve and to ensure the
camshaft is timed and synchronized
with the crankshaft position. correct sequence of valve timing, the camshaft is timed and synchronized with
the crankshaft position.
The cam lobes have a specifi c profi le that consists of a base circle and lobe to
provide the correct valve opening and closing characteristics ( Fig. 2.98 ). The
cam profi le is not necessarily symmetrical and the profi le may allow progressive
opening of the valve but with a sharp closing action depending on the
characteristics and optimization parameters of the engine.
Overhead valve (OHV) is used to describe an engine where the valves and
operating mechanism are located in the cylinder head. The valve gear transfers
reciprocating motion from the cam followers and camshaft. It is then passed to