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    Default 650 750 crankshaft

    i've been doing some digging and i'm hoping somebody here has some experience with this.

    is a 750 crank the same as a 650 crank?

    ive got a trashed 650 crank and a good std journal 750 crank, the journals are the same diameter but i know theres more to it than that,
    whats your thoughts on this?

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    Quote Originally Posted by MadMike View Post
    i've been doing some digging and i'm hoping somebody here has some experience with this.

    is a 750 crank the same as a 650 crank?

    ive got a trashed 650 crank and a good std journal 750 crank, the journals are the same diameter but i know theres more to it than that,
    whats your thoughts on this?

    1. the 750 crank has a 30 m/m timing side bearing that makes it the same as the 71-72 650 crank but it's different from the 1970 and before cranks.

    2. there is a difference in the primary drive gear snout, it's longer because of the triple row primary chain.

    3. the balance is different too so you will need to get it re-balanced or just put it together and see what happens.

    4. the 30 m/m 750 crank journal can easily be turned down to the 1 1/8" pre 71 journal.

  3. #3

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    Jul 2012
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    If your 650 is late '71-onward,the timing-side main bearing is 30 mm,same as a T140.The crankcase will be stamped "M" (metric) on the inside.
    As far as I know,crank counter-weight didn't change between 650 and 750.The different weight of pistons and rods caused the change in balance factor.
    As Torch said,the T140 crank is longer at the rotor end,because of the triplex chain.Not that hard to shorten.

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