Tappet Clearance

Tappet clearance is to allow expansion of valve spindle usually exhaust valve tappet clearance is greater than inlet valve tappet clearance.

For for measuring and adjusting tappet clearance :-

  1. Pushrod should be free (that is both inlet and exhaust valve closed). This takes place when engine is at firing TDC, check marking on flywheel.
  2. Open cam case cover and ensure that roller is on the base circle of cam.
  3. Fuel pump have a sleeve marking, topmark is beginning of injection and bottom is and off injection. Check the beginning of injection ( to be taken when engine is warm).
If Clearance is more : 
(hammering of valve stem)

  • Inlet valve opens late (blowdown decrease, loss of power, poor combustion).
  • Exhaust valve opens later (quality of air decreases, loss of power, smoky exhaust).
If Clearance is less

  • Valves opens early ( loss of compression,Pmax decrease, valve burning occurs.

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