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Thread: Help Chevy Flexplate question

  1. #1

    Help Chevy Flexplate question

    Just pulled an engine out, it was shaken (not stirred, LOL) The car had a bad vibration. After getting out the engine, noticed the block was a BBC 427 with a internal balance dampner, but the flexplate looked like it was for an external balanced engine. The flexplate had a counter weight, is this correct? or is there another way to tell? I guess my question is will an internal balanced engine flexplate be smooth (no counter weight welded to the flexplate)??

  2. #2
    Senior Member RACING JUNKIE
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    You have a 454 flexplate.An internal balance will NOT have a weight. Are you certain it isn't a 454? The block is the same. The old 512 casting block was used on both 454's and 427's...just a different crank and pistons.

  3. #3
    Senior Member RACING JUNKIE
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    You hit the nail on the head,

    Who put on the flex plate?
    "Can't Means You Don't Want To"

    Haven't You Stomped A Ford,,,,,,,,,,,, Lately?

  4. #4
    Senior Member MASTER BUILDER
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    My engines internal balanced. I buy internal balance flexplates (without weights), and I get them balanced too. You'd be surprised how unbalanced they are to begin with.
    It Ain't Over Til Its NOVA - 634ci of S*#t Your Pants!

  5. #5
    Tod74, how can I tell which it is 454 or 427 the cast # 3963512 by the location of the crank? I did not install the old flexplate, but I will get the right one and a new ATI dampner (to be safe) then take both the flexplate, dampner, along with the rest (the lightest rod, bearing, piston, rings, crank)

  6. #6
    Senior Member RACING JUNKIE
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    You Can't.....You can find out what it was from the facvtory by the suffix on the front pad, but you have no way of knowing(without pulling a head or pan) what crank someone has put in it since,other than the balancer and flexplate.... If that is a 512 block I WOULD NOT have it in a hotrod. Depending on the casting date they can bring big bucks. If it has a late 1969 cast date then it is a ls5 or ls6...chevelle and vette guys will pay big bucks for it if the dates are right ...I have 2 of them.One IS A Dec 68 cast 427 4 bolt main and one is a December 69 LS5 2 bolt main...It came in a chevelle with a manual trans.....It is damaged from a lifter failure because I didn't know it was worth anything and had it in my race car...
    http://www.chevelles.com/forums/showthread.php?t=289174

    I think they used the 512 block for several years after 70 so it may be just another 454 but I would look at the dates on the block and see.

  7. #7
    Well just my luck the stamp numbers are gone, block must have been decked... the heads are 3873858. Are there any other numbers I can find on the block, now I have the heads off and droped the pan

  8. #8
    Senior Member RACING JUNKIE
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    Quote Originally Posted by jjam
    Well just my luck the stamp numbers are gone, block must have been decked... the heads are 3873858. Are there any other numbers I can find on the block, now I have the heads off and droped the pan
    The casting dates on the block is what you want to look at to see if it's a valuable one...if it is 1970 or newer they will be on the bell housing flange...the older ones are on the side of the block down close to the pan rail. It will be something like L 19 9 Which means December 19 of 1969. If the block has a tall boss around the distributor in the lifter valley, the block is 1969 or older...If there is no raised boss around the distributor hole in the lifter valley it is 1970 or newer...or at least late 69 . You can't mistake this area I'm talking about it is very obvious.

  9. #9
    Senior Member RACING JUNKIE BEAST477's Avatar
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    Well since you have the pan and heads off, Measure the bore and stroke. That will tell you what you got.
    BEAST477






    Only a rich man can afford to use cheap parts.

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