What is Tappet Clearance? How to check And Adjust tapper clearance?

 What is Tappet Clearance Or Valve tappet clearance adjustment?

>Tappet clearance is a space between the top of the valve stem and the rocker arm. 
>Its purpose is to allow for some mechanical expansion and lengthening of the valve stem and push rods as the engine warms up. This clearance is also called valve lash.

 Why Tappet Clearance Is Given?
   >Tappet clearance is taken to ensure positive closing of the valve and for thermal expansion of the valve.

How To Check Tappet Clearance
1. Taking all safety precautions.
2. Make sure the piston is on TDC.
      i. From the marking on the flywheel.
     ii. From the fuel cam.
    iii. Push rod should be free. (both the valve should be close at this stage ie at the end of compression stroke)
3. Make sure the engine has cooled down.
4. Loosen the lock nut of the rocker arm.
5. Now adjust the tappet clearance between the rocker arm & valve stem by tightening or loosing the nut below the lock nut.
6. Use feeler gauge to adjust the suction valve clearance as .35mm an exhaust valve clearance as .45mm

Must Read:>Why Concentric Springs Are Fitted For Auxiliary Engine Head

                 What will happen if tappet clearance is less:

i.    Valve will open early & close late
ii.  Air induced through inlet valve may leak out. So, less air for combustion.
iii. Power will be reduced.
iv. Fuel consumption will increase, engine may become unbalanced, exhaust temp. will be very high.
v. In worst condition, valve may remain open, resulting in  loss of compression pressure, burning of exhaust valve, T/C fouling will increase.

What will happen if tappet clearance is more:

i.   Valve will open late & close early.
ii.  Lesser heat energy to T/C, so reduction in scavenge air & hence power.
iii. No proper removal of gases.
iv. Hammering of valve stem-may cause damage to valve stem.

 Image credit:dieselgenerators.tpub.com

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  1. nice post..good to learn about it, thank you.

    1. Glad to hear you got something from us... keep visiting.....

    2. This comment has been removed by the author.

  2. really usefull for me... thank you for this post :)

  3. Thanks for the knowledge sharing, really appreciated!

  4. I think u have confused the problems of tappet clearance. How can the valve open early and close late when tappet clearance is low and vice versa..

    And how can air leak out if the clearance is less. I think it would leak out if u provide more space to it (increasing the clearance).. Kindly answer me this question.


    1. v/vs open only when the rocker arm pushes it down... just think that clearance is too high that means time taken to reach rocker arm to the top of the v/v stem is increases that leads v/vs open late and vice versa......

      tapper clearance less means time period for valve being open is increases...At compression stroke inlet v/v remain open for some more time u can think what will happen then...! that leads air escapes... hope u got it... thkz for reading it..

    2. I got ur first point about the clearance being large..
      But when the clearance is less, the valve will open more quickly and obviously it will close quickly as well. So how could one expect that the air escapes out even when the inlet closes in less time. I think air will escape when the inlet remains for a longer time and allow the air to escape and this happens when the clearance is large..

      Isn't it???

    3. If tappet clearance is less then the valve will open early and close late.

    4. you are correct it will open more quickly.... but closing late...

    5. How is it going to be closed late? Can u please elaborate?
      It should take the same time to close as it takes to open...

    6. Mr.Mudassir, it is difficult to elaborate in words to u as u are keep on questioning without knowing the construction & working. To make u understand, u have to be elaborated practically. you must know the fuel cam profile, push rod, rocker arm and how all they connected & working. Then only u can imagine how the valve open early & CLOSE LATE is correct for tappet less.

    7. Hello Priyan,,

      I have recently studied the valve mechanism and all about tappet as I'm a mechanical engg student.. I have seen the working but this thing has gotten out of my mind that's why I can't get myself clear with the idea..

    8. Dude learn about cam nd follower

  5. Replies
    1. muddassir
      veenith is right , when clearance will be less, valve will be in open position for long period and closed for shor period.
      if clearance will be high valve will be in open position for short period and closed position for lond period.
      Hence opening of long period resulted for loss of air fuel mixture and short period means less mixture in cylinder

  6. Hey muddassir
    I have ans for u
    U knw one thing how valve get closed in engine, due to the spring force
    If clearance is less the contact duration between rocker arm and valve stm will be more so the valve will close late ... if all is normal than push rod push the arm and arm pushes the valve for opeing and when push rod stop pushing frther than sprind force closes the valve ...

  7. it is simple:
    less clearance : large area of contact between rocker arm & valve stem hence valve will remain open for long time , hence close late. rocker arm push the valve down for more time.
    more clearance: area of contact less between rocker arm & valve stem hence valve will remain open for less time but close for more time.hence open late

  8. Mr.Mudassir....little knowledge is dangerous....so before going into any arguement....pls study...

  9. What procedure should be used to check valve clearances on bmc 2.2
    Many thanks

  10. That is profound!

    Thank you for these engagements

    I am just learning


  11. That is profound!

    Thank you for these engagements

    I am just learning


  12. Great explanation, specially the symptoms....i was in search of the symptoms of bad tappet. This is the perfect answer on the internet..keep it up

  13. Great explanation, specially the symptoms....i was in search of the symptoms of bad tappet. This is the perfect answer on the internet..keep it up


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