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  1. #1
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    Plastigauge says clearance too large on New crankshaft

    Hi,

    I am plastiguaging my brand-new Scat 3.58 stroke crank (5.2L V8) with brand new (+0.000, Sealed Power 5095MA) bearings.

    I get 0.002 inches on the 1 and 5 bearings. I have not tried measuring the others.

    This is larger than allowed: No. 1 is supposed to have 0.0005 (min) to 0.0015 (max) --- according to Chrysler book.

    Tried removing the cap and lightly sanding the mating surface with a honing block to remove any hard gunk. Did tighten to 85 ft-lbs. Measured mains at 2.5005 exactly.

    I am still over 0.0015. I was really expecting a value close to the minimum since all the components are brand new.

    Can anyone help?
    Last edited by paulsheer; 05-20-2015 at 11:10 PM.

  2. #2
    Forum CONDUCTOR Man Z88Z's Avatar
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    Just a bump for ya....


    Did Scat recommend those bearings, or did they not give a recommendation? Either way, maybe contact Scat and see if they have ay ideas?

  3. #3
    Member dukefromthecave's Avatar
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    Do you have a caliper that will measure the crank journal?

  4. #4
    Member dukefromthecave's Avatar
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    I plastigauged the bearings when I assembled my bottom end and I seem to remember the internet consensus being that a little on the loose side like that is out of spec but reasonable to leave. Might have a tiny bit less oil pressure. if you rotate crank 180 and check again it shows if crank is not perfectly straight. i think I would be more concerned if the installed/torqued crank spins freely.

  5. #5
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    Quote Originally Posted by dukefromthecave View Post
    Do you have a caliper that will measure the crank journal?
    I wouldn't trust calipers for .0000 resolution. Micrometer HIGHLY suggested.

    - - - Updated - - -

    OP, don't rule out "plus" bearings. They are bearings +.001


    If you haven't lived for something, you'll die for nothing.

  6. #6
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    Well here is the update. I am putting in all the details in case anyone wants to use this as a reference.

    (BTW the 0.0020 above is hopeful reading -- it was probably closer to 0.0025)

    I used a dial bore gauge and digital micrometer (huge relief that I previously bought these --- thought I was never going to need them).

    Summit Racing recommended phoning the Sealed Power support line. Sealed Power gave me the spec on the cap bore diameter. This is 2.6925 to 2.6930. He said sometimes this diameter can widen

    on an old engine. Is this true? How can it???

    I measured my cap bore. It was slightly over in the vertical axis, but exactly right on the horizontal axis. Huh?? Weird!

    I used a 1000 grit Japanese honing block (for sharpening knives, but these things are amazing) to clean _both_ cap mating surfaces.

    Tighten up and measured again and I get 2.6925 in both directions. Yippee!

    Then I re-installed and plastiguaged again.

    This time I get 0.0020 exactly --- still out of spec.

    Now I ordered overnight shipping of Mahle Clevite MS1344P.

    The clevite bearings plastiguage at 0.0015. (Clevite's come shrink wrapped so there were no scratches. Sealed power came with no plastic -- bounce around in a flimsy box - *growl*.)

    So I'm keeping the clevite, and all is good.

    BTW the plastiguage is surprisingly accurate -- dial bore gives the same.


    I bought the ebook "How to Modify Your Mopar Magnum" by Larry Shepard for a few bucks. It says 0.0025 for racing engines. It says nothing about stock engines.

    I'm building a daily driver, not a racing engine; and the Chrysler-Jeep manual says it should be 0.0005 to 0.0020 except for No. 1 which should be 0.0005 to 0.00015. I also measured the

    journals and they are 2.5005 -- they are supposed to be 2.4995 to 2.5005 so the crank is _perfect_.

    One can check the Sealed Power bearing thickness -- but you need a round-headed micrometer for that -- I don't have one. The sealed power bearing at the crown is supposed to be .0957 for

    1, 2, 4, and 5, and .0959 for No. 3.

    Doing the math gives a clearance of 0.0006 -- huh??? How did we get from 0.0006 to 0.0020?????

    Something is uber phishy with these.


    I think the lesson here is:

    1. Use a honing block on the cap mating surfaces before install.
    2. Dial bore your caps before putting the bearings in.
    3. Trust your plastiguage if clearance is too large.
    4. Don't trust _any_ manufacturer to ship you a single working thing.

  7. #7
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    Good to hear you have it cleared up.


    If you haven't lived for something, you'll die for nothing.

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    Quote Originally Posted by Z88Z View Post
    Just a bump for ya....


    Did Scat recommend those bearings, or did they not give a recommendation? Either way, maybe contact Scat and see if they have ay ideas?

    i did not look for the recommended bearing when i bought all these.

    i assumed since they were stock size journals, and since it was not the "requires narrow bearings" type of crank, that any stock bearing would work.

  9. #9
    Member SilverXJ's Avatar
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    Scat seems to undersize their cranks a bit. Same issues with their 258 cranks for the stroker.

  10. #10
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    Quote Originally Posted by SilverXJ View Post
    Scat seems to undersize their cranks a bit. Same issues with their 258 cranks for the stroker.
    By how much? I do have a spiffy 1/20,000 digital micrometer and all journals are at the maximum end of the allowed range.

    Also note that I don't have the fancy crank -- just the cheep cast one.

  11. #11
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    Unless you just found out your micrometer was off by 3/10,000 because it was not calibrated. So the crank was 2.5002 all along.

    Well that still leaves the question open.

  12. #12
    Member dukefromthecave's Avatar
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    Gah! That's the problem with precision measuring tools, you almost need two. How did you verify?

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    The micrometer has a 2.0000" calibration billet. You measure it and it hit the Zero button.

    Before I hit the zero button it said 2.0003. So where that Scat was 2.5005 it must have really been 2.5002. Which is "normal".

    I should say for anyone looking at this thread in the future that my mistake doesn't resolve the question.


    But the engine is complete, so it's off my radar. Actually, just finished rebuilding the transmission.

    Now I'm waiting for transfer case parts... and then it will be hoisting time.

  14. #14
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    I found a way to measure the sealed power bearings. I have a 2.4" diameter billet from my seal-install kit. I measured the billet diameter with and without the main bearing against it.

    It seems these Sealed Power main bearings really are 0.00025 too thin. If you times 2 that's 0.0005 extra diametric clearance. This makes sense because the clevite was 0.0005 tighter than the Sealed Power. This means the Sealed Power bearings are measurably out-of-spec compared to figures their agent gave me.

    Mystery solved.
    Last edited by paulsheer; 07-01-2015 at 11:09 AM.

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