Hydraulic Tappets

Hydraulic Tappets or Lifters are not new for automobile industries, many automobile companies such as Bentley Volks Wagon are used this system in their vehicles way back 70’s.

Why Hydraulic Tappet?

To know this first we have to no the construction of Valve Mechanism. In normal solid tappet system cam lobe pushes the lifter upwards and due to its upward movement Push rod also moves upward because its directly connected to the lifters when and other end of the pushrod was connected to Rocker Arm which helps to open the Valve by pushing it downward against it’s spring. When engine runs for a while it will get heated due to combustion and mechanical action, due to this metal parts of the engine expends a little. Following diagram shows valve terrain.

In this diagram you can observe Valve clearance or Valve Lash, when we adjusting valve we must keep small clearance (around 0.15mm) between valve and rocker arm because when engine is cold there was in metal parts so it will run properly but after a while when it starts to heat the metal parts starts to expand and when it leads further pressure on valve and it does not allow the valve close completely to avoid this valve clearance is necessary.



Hydraulic tappet is mainly consists following parts.

1. Body
2. Plunger Assembly
3. Pressure Check Valve





Working:

When engine runs oil pump supplies oil to the hydraulic lifters body through oil channel, lifter consists a small hole on it’s body and through this hole it gets oil supply from the bore and there after passes inside the plunger through plungers oiling hole. When plunger filled with oil it pushes the check ball against its spring and enters into the pressure chamber.

Now the whole lifter was filled with oil when cam shaft rotates its lobe pushes the lifter body upward with pressure when lifter get pressure from the lobe it tries to move upwards so it pushes the check ball and spring due to this action ball moves upward and closes the oil supply hole of the plunger now the oil stuck between lifter and plunger i.e. in pressure chamber is acts as a cushion. Cam lobe pushes the lifter body further upwards now the whole body acts like a solid Tappet / Lifter and moves upwards and push the valve against its seat via push rod and rocker mechanism.

When cam lobe turn downwards it withdraw pressure from the lifter body now the valve spring pushes the whole mechanism i.e. rocker arm, pushrod and lifters down wards.

In this system there was no need to keep valve clearance or lash because whether engine is cold or hot there Hydraulic lifters always get oil and according to the pressure it self adjust the clearance. So these tappets are called self adjusting tappets.

Merits:
1. Self adjusting Tappets / No adjustment is required
2. No clattering noise at cold engine condition
3. No power loss at hot engine condition
4. Smoother operation


To proper trouble free working of hydraulic lifters oil should be changed in correct period. Dirty oil cause to spoil the lifer body and plunger mechanism and it also leads to blockage of oil supply hole and it leads to improper working of lifters. When installing brand new tappets it must be it must be initially filled with proper grade of oil, oil strainer cleaning / changing also made in proper intervals.