CRANKSHAFT, 51-54 or 55-56?

Lee ODell
Lee ODell Senior Contributor
edited February 2011 in HUDSON
I have a 1955 308 engine and I wanted to know if it had a 51-54 or 55-56 crankshaft. This information is for all with same question about there engine.

Thanks to Walt Mordenti I have the answer.

If there is a 1/2" spacer between the crankshaft and flywheel it is a 55-56 crankshaft.

Mine didn't have the flywheel mounted. So:
Measure from back of block, by the seal, to the flywheel side of the crank flange.
If it measures 1 1/2" it is 51-54 crankshaft.
If it measures 1" it is 55-56 crankshaft.

Now I know my 55 engine has the 51-54 crankshaft.

Thank you Walt, you get more Karma for this information.

Lee O'Dell

Comments

  • bob ward
    bob ward Senior Contributor
    This won't help you tell which crankshaft is which, but they also have different flywheel bolt patterns.
  • Lee ODell
    Lee ODell Senior Contributor
    edited February 2011
    bob ward wrote:
    This won't help you tell which crankshaft is which, but they also have different flywheel bolt patterns.

    You are right Bob, it does't ID bare cranks. But it does help if the intent is to instal a 55-56 engine into a stepdown. Especially, since the 56 only had one crankshaft and the 55 came with both 51-54 and 56 type crank.

    It would be helpful to be able to ID a bare crankshaft at a swap meet or anywhere else. That brings up some new questions.

    What are the differences between bolt holes? Measurements.

    Would the measurements I mentioned be close, if measuring from the crank flange to the rear seal surface of the crank? If not what would the measurements be.

    Are there any other differences that may be measured?

    Is there a part number on the cranks?

    Will someone provide the information to ID a bare 308 chankshft?

    Lee
  • bob ward
    bob ward Senior Contributor
    Its a while since I've looked at the ends of 308 cranks, but I think there are 2 different flywheel flange diameters as well. That would be one sure fire method of on the spot crankshaft ID, I'm sure someone on here will know what the differences are.

    Another ID method would be to know the 2 dimensions from the flange to the rear bearing journal, there will be 1/2" difference between them.

    I've always assumed (dangerous I know) that Hudson made the ends of the stepdown and hash cranks different to prevent the incorrect interchange of flywheels and flexplates.
  • [Deleted User]
    [Deleted User]
    If it has 6 holes and bolts through them it's a 51 to 54. If it has threaded holes, it's a 55 or 56. Walt.
  • Lee ODell
    Lee ODell Senior Contributor
    walts garage-53 wrote:
    If it has 6 holes and bolts through them it's a 51 to 54. If it has threaded holes, it's a 55 or 56. Walt.

    Can't get any simpler then that. Thanks Walt.

    Lee
  • dougson
    dougson Senior Contributor
    walts garage-53 wrote:
    If it has 6 holes and bolts through them it's a 51 to 54. If it has threaded holes, it's a 55 or 56. Walt.


    So are the diameters the same?
  • [Deleted User]
    [Deleted User]
    What's the difference, can't use the flywheel from one to the other. Walt.
  • dougson
    dougson Senior Contributor
    walts garage-53 wrote:
    What's the difference, can't use the flywheel from one to the other. Walt.

    Wasn't my question.
  • bob ward
    bob ward Senior Contributor
    The flywheel flange on a 55/56 308 crank is 4.5" diameter. Can't help on the stepdown variety at the moment.
  • [Deleted User]
    [Deleted User]
    51 to 54 crank flange measures 4.000 to 4.025. I have 2 and this is what each measures. Doesn't mater as the flywheel has a larger opening, up to 4.075 Walt.
  • [Deleted User]
    [Deleted User]
    another simple identifier is the stepdown crank flange has one hole that is unequally spaced on the pitch circle and hash are equidistant.
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