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Thread: Crank questions

  1. #1

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    Crank questions

    Looking for definations for the following, regarding crankshafts

    1) Trued, how can you tell if it is true w/ in tolerance

    2) Phase, how do you tell if the crank is in phase

    3) Index, what the heck is this?


  2. #2

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    Anyone?

    I took my crank to a shop the other day to check for trueness. All he did was put it on v blocks, use his dial gauges, and spin the crank? Is that all there is to it?

    And phase... I did some reading, and know how to find out if it is in phase while in the case, but what about out of the case?

    Isn't there a good educational article about cranks?

  3. #3
    96XPSS's Avatar
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    Sorry...I read this and was in hopes someone else would post? Come on Dan...quit being a chicken... So...here is my explanation.

    1) Trued, how can you tell if it is true w/ in tolerance?

    The less the crank is misaligned (crooked), then the faster it will spin. Laying the crank in the bottom case, and placing a dial indicator on the snout of the crank, and slowly turning it will check it for trueness (straightness). The same can be done at the rear of the crank. They have special jigs when they press a crank together to get it right. Optimum is .001" runout.

    2) Phase, how do you tell if the crank is in phase?

    Phase is just a technical term designed to confuse you...he he
    Each rod should be placed on the crank 180 degrees from the other, and anything else is considered "out of phase."

    3) Index, what the heck is this?

    The front (snout) of the crank has to be indexed, as in the keyway has to be in a certain location for the flywheel, and more importantly the mag cup, to align with the inductive pickup so that it fires the spark plugs at the exact time required for optimum power.

    Others will hopefully chime in now...

  4. #4
    Tool Bag water worx's Avatar
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    Sounds about right to me,RQ knows is chit.

  5. #5

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    Quote Originally Posted by 96XPSS View Post
    Sorry...I read this and was in hopes someone else would post? Come on Dan...quit being a chicken... So...here is my explanation.

    1) Trued, how can you tell if it is true w/ in tolerance?

    The less the crank is misaligned (crooked), then the faster it will spin. Laying the crank in the bottom case, and placing a dial indicator on the snout of the crank, and slowly turning it will check it for trueness (straightness). The same can be done at the rear of the crank. They have special jigs when they press a crank together to get it right. Optimum is .001" run out.

    2) Phase, how do you tell if the crank is in phase?

    Phase is just a technical term designed to confuse you...he he
    Each rod should be placed on the crank 180 degrees from the other, and anything else is considered "out of phase."

    3) Index, what the heck is this?

    The front (snout) of the crank has to be indexed, as in the key way has to be in a certain location for the flywheel, and more importantly the mag cup, to align with the inductive pickup so that it fires the spark plugs at the exact time required for optimum power.

    Others will hopefully chime in now...

    Thanks 96. I think I get it.

    To be out of true, the webs would have to be on the pins at an angle?

    The phase, after going out to look at a crank, it appears the entire web assembly would have to spin on the pins? What are some things that would cause this to happen? How can I prevent it? How can I check it while out of the motor to make sure they exactly 180* apart?

    Index, I see that the key way is lined up with the front rod at TDC. How the heck does it get out of index without taking it apart and putting it back together wrong?

    Any suggestions on where to buy a gauge and some v blocks at a good price? I also need a TDC gauge. Not starting a shop so nothing super expensive is needed. Just enough to get the job done right.

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