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GM bell housing bolt sizes

Discussion in 'The Hokey Ass Message Board' started by Voh, Aug 13, 2012.

  1. Voh
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    Voh
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    Can anyone tell me the sizes for the taps on a GM bell housing? The four that bolt the gear box on, the one for the clutch fork and the little ones for the inspection cover. Are they standard or metric? I know the four are larger than 3/8". I had one of those.
    Thx
  2. barslazyr
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    barslazyr Member

    The four that holds the box on are 1/2"x 13, Inspection cover is 1/4" x 20.
  3. squirrel
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    squirrel Member

    It would help if you tell us what GM bellhousing it is. If it's an old one, then it should have 1/2" coarse for the trans, and 1/4-20 or possibly 5/16-18 for the cover.

    If it's from some "modern" GM it might be metric, or a combination, or who knows what.
  4. Voh
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    Voh
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    Here is the number on my bell housing.

    Attached Files:

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  5. Voh
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    Voh
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    Have another question on it as well. Can it be run on a block that is tapped for a top bolt? Bell housing does not have a top/center hole.

    Attached Files:

  6. squirrel
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    squirrel Member

    Chevy hardly ever used the top hole. Six bolts is plenty.

    That's a normal chevy bellhousing. Make sure it's the right size for your flywheel, they made small and large. They also had a few other differences...make sure it fits the transmission "snout", some had a larger center hole in the bellhousing to fit the larger truck transmissions. If it's a loose fit the transmission could jump out of high gear. If it's too tight you can't put the transmission on all the way.
  7. Voh
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    Voh
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    So I got more questions. As it turns out the flywheel on the motor is a 168 tooth flywheel and the bell housing is of the "383" part number family.

    What do I need to do? I don't have the clutch yet so it can go either way. Do I go smaller flywheel/clutch or different bell housing?

    It will be a simple 283 not of high HP or anything. T5 transmission and a 1965 lemans axle, 3.08 gears.


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  8. oldolds
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    oldolds Member

    Starter matches flywheel. It bolts to engine not belhousing. Make sure the bell fits over the flywheel. I am not a numbers guy, I usually go by fit.
  9. gimpyshotrods
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    gimpyshotrods Member

    The 383 bellhousing fits a 153 tooth flywheel or flexplate, only. You will need a 153 tooth flywheel, and a 10-1/2-inch clutch, which is more than enough for all but the craziest of SBC's.
    Last edited: Sep 19, 2012

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