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  1. #1
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    Default externally balanced 383 flexplate

    Long time reader first time poster.
    Quite a few years ago i had a mild 383 stroker engine built and dynoed . It made 435 fp torque at 3500 and 389 hp at 5100, so a mild street engine. After the dyno runs and tuning the guy told me to get a externally balanced flexplate and bolt it into the car .Fast forward to now ,i have been working on the car again and have been thinking about the balance of the engine. How did he balance the engine without the flexplate ,is this possible with a externally balanced engine and do i need to rebalance it with the new flexplate

  2. #2
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    hi
    U need to follow the instructions by the original engine builder. Was the engine originally balanced with an external balanced flex plate ?? Install position and weight is dedicated to that rotating assembly .

  3. #3
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    Thanks swampy .He had his own flexplate that he ran on the dyno. Dont know how it was balanced , The only instructions i was given was given was you need an externally ballanced flexplate. I can see on the balancer several holes drilled into the weights but can it be balanced without the flexplate you are going to use

  4. #4
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    Are you fitting a new flex plate & you are worried about differences in balance between old & new? If so, get the new FP balanced to the same specs as the existing one.

  5. #5
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    No ,i didnt supply a flexplate as i didnt have one ,the engine was out of a manual car so i dont know what it was balanced with.

  6. #6
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    Hi
    U need to find out who the builder is/was..
    Are 383 always externally balanced ??? This is the only reason you need a weighted flex plate/flywheel.
    Also cranks canbe balanced differently front to rear . Is yours ??

  7. #7
    casual poster Willie's Avatar
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    400 Chev motors are externally balanced. If your crank is an original Chev crank you may need to externally balance the motor- flex plate and harmonic balancer. Some aftermarket 400 cranks are balanced however.

  8. #8
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    The crank is a eagle cast crank which is externally balanced ,it has dowl pins on the crank so the flexplate can only be installed one way ,the balancer is a romac with counterweights on the inside of the hub . When i picked up the engine i was not given a flexplate and from what i have read a externally balanced engine that is not stock needs the ballancer crank and flexplate to be balanced as a unit. I suppose the question i am asking is if i bolt on a off the shelf externally balanced flexplate will i be right or does the engine need to be disassembled and rebalanced
    It has been that long since the engine has been built that if the guy who built the engine is still in business i would doubt he would have any records of my engine

  9. #9
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    HI
    A lazy balancer will external and other end internal . I have had this from balancing quotes for my forged steel chev . Performance is considered all internal.
    Some cast cranks are designed to be external balance F & R
    Which ever end is external balanced it has a flexplate and /or balancer that's corresponding . If ever these parts are replaced they must use the exact same balanced parts [done at machine shop] and installed in the same way .


    If u miss place the balancer and or flex plate yep it would be an issue . Need to speak to a competent builder with balancing facilities .
    Last edited by swampy; 13-07-2019 at 02:01 PM.

  10. #10
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    Thanks for the replies, i will see if i can get in touch with the engine builder and see how they balanced it and if that fails talk to a decent engine builder .looks like it might be comming apart again

  11. #11
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    If it is an externally balanced 383 then a 400 flexplate will sort it out for you.

    MOST balance jobs retain standard external counterweighting for this exact situation.

    JMHO

  12. #12
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    hi
    Struggler
    If the use of a 400 flex was suitable . Does this make the assumption the balance is not really that accurate anyways . 1 size fits all approach ?

    eg quote from Repco was 10 gram+-
    eg speed shop 6 gram street car and under 2 gram for high revving mtr

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