Page 147 - 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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Engine systems 131

Figure 2.99 Overhead valves (OHV): 1, rocker shaft bolt; 2, push rod; 3, lubrication passages;
4, exhaust valve; 5, cam bearing journal; 6, cam lobe; 7, hydraulic tappet; 8, turbulence ramp;
9, inlet valve; 10, rocker

Figure 2.100 Double overhead camshaft engine (DOHC): 1 and 2: tensioner wheels; 3, timing
belt; 4, inlet cam; 5, exhaust cam; 6, distributor drive; 7, valve

the valves via push rods and a rocker assembly, which acts on the valve stems
Key fact
( Fig. 2.99 ).
Overhead cam (OHC) refers to
Overhead cam (OHC) refers to the position of the camshaft in the engine; that
the position of the camshaft in the
is, it is positioned in the cylinder head. There are various designs using direct
engine.
or indirect mechanisms to convert the rotating cam motion into a reciprocating
motion, and then transfer this motion to the valve stems. These designs are
proposed to facilitate a close tolerance in operating clearances.

A further development, now employed extensively, is the use of twin or double
overhead camshafts (DOHC) ( Fig. 2.100 ). These can use direct or indirect valve
actuation and are well suited to multivalve engine designs, including those with
variable valve timing.