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Thread: How Easy Should Crankshaft Spin

  1. #1
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    How Easy Should Crankshaft Spin

    I have taken apart my 1973.5 911 T engine with 123k miles. I am trying to figure if I need to ship my crankcase out west for align bore. I gave it a good enough rough cleaning, then cleaned the bearing journals, old shells, and crank shaft real well, to do the spin test. I gave the shells a thin wipe of moly assembly lube, but then thought maybe that's too thick so layered in a film of oil to boot. To get an idea of the base line friction, I put the crankshaft in the open half and gave it a spin by hand with a couple flywheel bolts for grip. It turned easily but not so much that it would keep turning hardly at all past where I let go even with a hard turn. Torqued up the case and seems about the same, but I can hear slight friction at about a third of the rotation. Still spins the same I think. I read that sometimes crankshafts can keep spinning for a few seconds. If that is the standard, I am miles away, but still totally free. Good enough or is this case going out west? thanks!
    Member #3896
    1973.5 911 T
    1974 911
    1974 CB750K

  2. #2
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    just send it to Ollie's in Arizona and get the case align bored. You do not want to rebuild it again . And have the crank serviced as well
    1. Chris-Early S Registry#205
    2. '70 911S Tangerine
    3. '68 911L Euro Ossi Blue

  3. #3
    Most, if not all, mag cases are not longer in spec once they have been taken apart. They kind of warp when you split them.

    Having it measured is the minimum you should do. While at it get your crank inspected, magnafluxed and cleaned. If you know that your crank and case are good you kind of know that you probably don’t have to split it any more in the future unless there is a failure.

    Richard
    searching for engine (case) 903742

  4. #4
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    After you have torqued everything right, a short, dry hit with a copper hammer at the flywheel side to loose possible tensions. But not a hit destoying the shaft ! Then test it again.

  5. #5
    The crank will not keep spinning for a few seconds. But you do need to test with NEW bearings.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  6. #6
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    How much rotation is enough?

    Quote Originally Posted by edmayo View Post
    The crank will not keep spinning for a few seconds. But you do need to test with NEW bearings.
    I will try with the new bearing for sure. Keep spinning for a few seconds does seem like quite a lot. But should I at least get a quarter turn past letting go? Even with a quick turn by hand I get almost nowhere past letting go. Many thanks for the help!
    Member #3896
    1973.5 911 T
    1974 911
    1974 CB750K

  7. #7
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    Assembly lube is thick and sticky. I'm no engine builder but I wouldn't expect it to spin down like a lightly lubed ball bearing with assembly lube on the crank bearings.
    A part isn't purchased until paid.

    The 9 Store LLC.

  8. #8
    Senior Member uai's Avatar
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    I'd say it won't spin at all.
    Just a gut feeling new crankshaft with break in oil perhaps 4-6Nm (only crankshaft)

  9. #9
    Quote Originally Posted by Chickenstrips View Post
    ... and gave it a spin by hand with a couple flywheel bolts for grip... I read that sometimes crankshafts can keep spinning for a few seconds...
    It could with a flywheel attached, and it depends on how hard you spin it.
    Without a flywheel, I wouldn't expect it to continue spinning very much on momentum alone.

    Jon B.
    Vista, CA

  10. #10
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    I have done this a few times to check mag cases. New bearings with motor oil, a proven std/std straight crankshaft. Bolt and torque the case through bolts and check crank rotation by turning with a wrench on the crank pulley bolt. If the case is straight, the crank should turn smoothly, with little torque with no binding.
    Tom Butler
    1973 RSR Clone
    1970 911E
    914-6 GT Clone in Progress

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