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Thread: crankshaft thrust bearing installation

  1. #1

    crankshaft thrust bearing installation

    Tryed to install the rear main bearing today. With no cap there's 0.008 end play. After cap installation, there's 0.007. So bearing halves are not aligned or something else is wrong. Tryed to move crank back and forth many times, no help. Any ideas what to try next?

    BBC Gen V 502 block and crank.

  2. #2
    Senior Member DYNO OPERATOR
    Join Date
    Jan 2004
    central Illinois


    If the difference is only .001" that is acceptable. .006"-.010" is normal depending on auto or manual trans.

    If you want to try again, snug up the rear main only and carefully pry with a big screwdriver forward and back and then torque and see if it changes any.

  3. #3
    Senior Member RACING JUNKIE curtisreed's Avatar
    Join Date
    Feb 2004
    I do it a little different than Mark. I do check with the bottom half only as the OP did, then install the cap and take a plastic mallet and tap the crank forward to get the halves even with one another. This is just to set the thrust then torque the cap down. If after doing this you still can't get what you want you can sand the thrust down by laying very fine wet or dry sand paper on glass or a surface plate and carefully sanding the thrust surface down.

    I do check total movement back and forth like Mark has posted by prying.


  4. #4
    Late night at the garage yesterday. We also tryed the sanding trick to the bearings, put them on the straight table and rubbed against 400 paper and got now 0.009 without cap and 0.0085 with the cap. Also, now the thrust bearings are much cleaner looking, no black stuff on them anymore. I will mic the bearing halves again when I got more time to make sure they're ok.

    I also found that if you have oil (20W50) between thrust bearing, it will eat up 0.001-0.00015 out of clearance when you move the crank just with you hands. Of course with a breaker bar or similar tool you can break the oil film out.

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