"Overlap Cycle"

Discussion in 'Engine, Fuel and Exhaust' started by 90FXRS, Apr 12, 2011.

  1. 90FXRS

    90FXRS Junior Member Contributor

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    What is meant by this term? It's mentioned in the instructions when installing adjustable pushrods.
     
  2. TripleJ

    TripleJ Senior Member

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    I believe it refers to a short period while both the exhaust and intake valves are open at the same time.
     
  3. R_W_B

    R_W_B Senior Member

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    That's what I was thinking but I've never adjusted pushrods so I figured it meant something specific to them. It might be referring to staying away from that part of the cam-crank rotations as far as setting the gap. In other words I would think to set the gap it would have to be when the valve was not being lifted.
     
  4. Hoople

    Hoople Account Removed

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    Since there is 720 degrees of rotation for a complete cylinder cycle, there are two Top Dead Centers for each complete cycle. One is at TDC of compression when the spark fires when both valves are fully closed. There is also another TDC at the end of the exhaust cycle. This is the overlap TDC when the exhaust valve closes while the intake valve is opening.

    You would not want to adjust the push rods while on the TDC of valve overlap because the lifters would not be on the base circle of the cam.
     
  5. 90FXRS

    90FXRS Junior Member Contributor

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    So just do it the way I've always done it. Watch the intake close and rotate the motor to TDC, adjust that cylinder. Repeat for the other cylinder.
     
  6. Jack Klarich

    Jack Klarich Expert Member

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    Best and only way to avoid a bent valve:s