Page 144 - 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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128 Automobile mechanical and electrical systems

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Figure 2.93 OHC value rotator features: 1, exhaust cam; 2, inlet cam; 3, cam bearings;
4, rotator; 5, inlet valve; 6, inlet port; 7, exhaust valve; 8, exhaust port; 9, spring; 10, follower

Figure 2.94 Valves in position on a cutaway engine. (Source: Ford Media)

2.1.3.5 Valves
Inlet and exhaust valves are poppet-type valves with a circular sealing face
recessed in the cylinder head ( Fig. 2.94 ). The valves are located via the stem and
slide inside valve guides mounted in the cylinder head. Valve heads are exposed
to full, combustion chamber temperatures and pressures; the temperature of the
exhaust valve can be as high as 800°C. The incoming gas charge has a cooling
effect on the intake valve but, generally, heat dissipation from the valves is via the
stem and guides to the cylinder head. Combustion and fuel deposits can cause
problems on the valve; this can be avoided by the use of good quality fuels
and oils.
The total valve opening area is always greater for the inlet valves; this is to increase
the volumetric effi ciency of the engine since the pressure difference across the
inlet valve, when charging the cylinder, is much lower than the pressure difference