SHOP MANUAL MT26-31 - 06.2005
Engine
Tier-3 710655-
Ch 1 page 46
The purpose of the valve mechanism is to actuate the
valves, causing them to open and close at the right times in
relation to the position of the crankshaft and piston.
The camshaft is located high up and driven by the timing
gears at the rear end of the engine so that it rotates at half
the speed of the crankshaft.
The camshaft cams (lobes), two for each cylinder, actuate
the valve tappets.
The pushrods have one end in the tappets and the other
end, via the rocker arms, transfers the movement from the
camshaft cam to the valves.
At one end of the rocker arm is an adjusting screw, the
spherical lower end of which rests in the pushrod so that the
tappet follows the camshaft at all times.
The correct clearance can be set with the adjusting screw to
ensure that the valve will close properly during combustion.
The valves seal against valve seat rings which are pressed
into the cylinder head to make a tight fit.
The valve seat rings are made of extremely durable material
to give them a long service life.
Should it be necessary, they are replaceable.
With four valves per cylinder, the total valve area becomes
greater, making it easier to fill the cylinder with air. At the
same time, less energy is consumed in forcing out the ex-
haust fumes.
The effort required for gas flow is reduced and engine ef-
ficiency is improved. This in turn leads to a reduction in fuel
consumption.
The injector can be located centrally, which improves com-
bustion and results in reduced emissions and lower fuel
consumption.
Valve mechanism
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