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  • Engine: Crankshaft Quality

    The machine shop performing the machining on my stude short block and crank called me this morning and gave the following comment on the qualilty of a Stude 289 crank I sent them out of a GT 289 engine. Said the crank quality was on the level of a Sonny Bryant racing crankshaft. Not bad feedback for an OEM forging.

    This was the second crank I delivered to them. They rejected the first crank because it has been turned wrong on the rod radius journal by a previous machine shop many years back. Shows that all machine shops have different values on quality of the work so Beware!
    Start and Stage Your Studebakers

  • #2
    My understanding is that when having a crank ground you need to specify "radial grind" for best crank strength. You will pay more!

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    • #3
      As said...just depends on the overall quality of the shop..!

      The two shops I use will always go as large a radius as required by the rpm being used.

      Normally, for a race like application, .125" is average. .070"/.090" is fine for the street.
      But if that can't be done, actually a .010"/.015" deep "undercut" at each end of the bearing surface also works very well. You just need a good "stress relief" area in the 90 degree corner for flex to take place without adding any damage.

      And I've seen pictures of crank flex....! Even the 90ish pound Top Fuel crank shafts flex.

      BUT....remember...stock bearings will NOT clear a race inspired... .125" radius. You must chamfer them yourself.

      Mike
      Last edited by Mike Van Veghten; 08-17-2011, 11:08 AM.

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      • #4
        They rejected the first crank because it has been turned wrong on the rod radius journal by a previous machine shop many years back.
        My understanding is that when having a crank ground you need to specify "radial grind" for best crank strength. You will pay more!
        The two shops I use will always go as large a radius as required by the rpm being used.
        FWIW, on a usual .010" to .020" regrind, the grinder cannot materially increase the radius. With so little material being removed, the regrind can't add much radius, but they can screw it up by removing whatever radius is there and leaving a square corner. As Mike said, that isn't a good thing.

        Having said this the Studebaker V8 crankshaft is so strong, on a stock rebuild or typical street hop up, you'd never see any difference in durability.

        jack vines
        PackardV8

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