Lesson 1/Learning Event 1
FIGURE 35. HYDRAULIC VALVE TAPPET.
Hydraulic valve tappets are used on many engines. These tappets make minor valve clearance adjustments
automatically each time a valve closes. This way, all the tappet noise is stopped because the engine is operated
without any valve stem to tappet clearance.
Basically, a hydraulic valve tappet is made up of a cylinder fitted with a plunger or piston and a ball-check valve.
Oil under pressure is forced through the ball-check valve into the cylinder below the plunger when the tappet is
on the base circle of the cam. This raises the plunger which, in effect, increases the tappet's length and
removes all clearance in the valve linkage. When the lobe lifts the tappet, oil tries to flow out
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