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A tappet is a component of an engine’s valve train that comes into contact with the camshaft’s lobes to actuate the opening and closing of the engine’s valves.


  • Tappets are also known as lifters or cam followers.
  • They transmit the motion of the camshaft to the valves.
  • When the camshaft rotates, the lobes on the camshaft push against the tappets, causing them to move up and down.
  • This motion is then transferred to the pushrods or directly to the rocker arms, which ultimately open and close the valves.


  • There are various types of tappets, including flat tappets, roller tappets, and hydraulic tappets.
  • Flat tappets have a flat surface that contacts the camshaft.
  • Roller tappets have a rolling contact surface, reducing friction and wear.
  • Hydraulic tappets contain a hydraulic mechanism that automatically adjusts for valve clearance.


  • In engines with adjustable valve clearances, the tappets can be adjusted to maintain the correct clearance between the valve stem and the rocker arm or camshaft.
  • This adjustment is typically done using a screw mechanism located at the top of the tappet.
  • Proper valve clearance ensures optimal engine performance and longevity.


  • Tappets are often made of hardened steel or other durable materials to withstand the repetitive motion and high loads experienced in the engine.


  • Regular inspection and maintenance of tappets are essential to ensure proper valve operation and prevent premature wear.
  • In engines with hydraulic tappets, periodic checks of the hydraulic fluid level and condition may be necessary to maintain proper adjustment.

Overall, tappets play a critical role in the operation of an engine’s valve train, translating the rotational motion of the camshaft into the linear motion needed to open and close the engine’s valves at the correct timing.

See Related Terms

  • Barrel tappet
  • Bucket tappet
  • Cam follower
  • Flat tappet
  • Hydraulic tappet
  • Mushroom tappet
  • Valve tappet
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