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Projects Tapping a 60s Chevy crankshaft

Discussion in 'The Hokey Ass Message Board' started by IowaTom, Oct 30, 2019.

  1. IowaTom
    Joined: Jul 23, 2018
    Posts: 26


    Guys - I'm rebuilding a '65 vintage 283 and trying to get the harmonic balancer on without a big hammer. I was able to tap a 3/8 by 24 thread in the crank end but I'm afraid it wasn't strong enough and I'm having to re-tap to the next larger 7/16 by 20, as the factory did on later engines. I'm having trouble getting the tap started even after drilling the hole out with my 3/8ths bit. I hesitate to use anything larger, because it'd be a 7/16ths and that won't work if I want to thread a bolt in, that size. Is there a secret to getting a tap started? I prefer to press this balancer on rather than whack away at it. and crank steel is anything but mild! :)
  2. DDDenny
    Joined: Feb 6, 2015
    Posts: 14,854

    from oregon

    It may not be the cheapest approach but paying to have someone machine a sleeve that slides over the crank snout with a piloting hole is about the only way to ensure maintaing a "true" center short of disassembling the engine and having the work done on a lathe.
    With removable pilot bushings it could be used as both a drilling fixture and a tapping fixture.
    Hnstray likes this.
  3. Hnstray
    Joined: Aug 23, 2009
    Posts: 12,021

    from Quincy, IL

    There is a tool for that purpose. I am thinking has such a tool available. If not there, the tools is available elsewhere. Worth looking for to get the job done accurately. Just had it done at my local high performance automotive machine shop on my 250 Chevy six build.

  4. Mimilan
    Joined: Jun 13, 2019
    Posts: 843


    Don't tap it, Just heat the balancer in the oven.

    Then use a piece of tubing large enough to go over the crank snout ,and bash away!
    You can hear to tone change when it is hit home.

    If you use some Aerosol "freeze spray" on the crank, you could probably push it on by hand

  5. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,695

    Member Emeritus

    Never had any issue driving a dampener on with a cut section of 3" thick, 4" diameter round stock, and a good sized hammer. Keep the block of steel centered, and hit it in the center, and methodically. And yes, the tone change tells you it's set. I don't even have the "install tool" for cranks that are tapped; they get their dampener driven on also. The only thing is, the dampener then has to be repainted. I am Butch/56sedandelivery.
  6. Hnstray
    Joined: Aug 23, 2009
    Posts: 12,021

    from Quincy, IL

    BRUTE FORCE is Traditional! :D
    Last edited: Oct 31, 2019
  7. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 1,335

    Tickety Boo
    from Wisconsin

    To cut a 7/16 20 thread, drill hole depth 1st with a letter U Tap drill, your tap should start easier ;)
    For any other size, check a drill and tap chart to cut correct hole size :)
  8. IowaTom
    Joined: Jul 23, 2018
    Posts: 26


    Really? I won't risk messing up crank thrust, seals or bearing seats by whacking on the balancer?
    It's got a rubber cushion and I hesitate to stick it in my oven. Guess I'm over cautious. Thanks all!
  9. krgdowdall
    Joined: Apr 3, 2015
    Posts: 108

    from Alberta

    The Tap Drill for 7/16-20 thread is 25/64 Purchase the correct size drill ( Good Quality ) and tap
    along with some "Cool Tool" or "Rapid Tap" tapping fluid. You may have to go to an industrial supply to find these rather than the hardware store. Use plenty of fluid both drilling and taping.
    Keep the drill square with the snout and the Tap and handle square while tapping. Turn in 1/8 to 1/4 turn and back out to clear the chips. You may need a "Bottoming Tap" depending on the bolt length. hole depth required.
    j-jock and Hnstray like this.
  10. 01mikep
    Joined: Jul 26, 2014
    Posts: 125

    from California

    I have a 327 in the works right now and the crank is not tapped. When I dropped the block at the machine shop I asked them to tap the crank too ($80 fee). I asked for this not for ease of install but to prevent it walking off (even if it's rare).
    Hnstray likes this.
  11. Mimilan
    Joined: Jun 13, 2019
    Posts: 843


    I wasn't referring to a furnace. 200 degrees max
    Engines get up to 200 deg constantly. The 4 rubber contact patches on racecar tyres get over that.

    What you're trying to do is install a warm balancer onto a cold crank snout [before the temps equalize]

    You're hitting on a 6 pound damper with a 3 pound hammer onto a 45lb crank
    How much force is transmitted to the crank trust bearing? [you can always wedge a block of wood between the rear crank flange and the engine stand]
    Last edited: Oct 30, 2019
    Hnstray and j-jock like this.
  12. Hammering a dampener on is terrible advice, it’s a fantastic way to totally fuck up a thrust bearing and endplay.

    Sent from my iPhone using H.A.M.B.
  13. Driver50x
    Joined: May 5, 2014
    Posts: 140


    Hammering a balancer on is not the best way to do it, but I’ve seen it done plenty of times without a problem.
  14. There’s plenty of shit that happens supposedly without problems, doesn’t make it right

    Sent from my iPhone using H.A.M.B.
    Truckdoctor Andy likes this.
  15. deucendude
    Joined: Oct 31, 2008
    Posts: 598

    from norcal

    If you heat it to 200 degrees in a oven it should tap on rather easily.
  16. chargin03
    Joined: Jan 8, 2013
    Posts: 491


    Beat it to fit and paint it to match.
  17. coilover
    Joined: Apr 19, 2007
    Posts: 650

    from Texas

    There is a guy on the Stovebolt Forum that goes by the handle Hot Rod Lincoln that has a guide set up for crank drilling/tapping that I think he rents out for a very reasonable sum.

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