Rod end gap clearance question
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Rod end gap clearance question

  1. #1
    1976 Sanger Flattie Running_on_Empty's Avatar
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    Default Rod end gap clearance question

    I am building a stoker bbc....its a gen 4....the crank is a 4.250....all parts were bought brand new from the same place....my question is this...mercruiser manual says .013-.023(service)...manufacturer says .018-.024....but my clearances are between .008 and .011....I personally have never herd of machining connecting rods....but maybe I'm missing something....or is there another spec for production? If I need a bigger clearance how would one go about attaining it?

    -thanks

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    Gone
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    Rod side clearance?

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    1976 Sanger Flattie Running_on_Empty's Avatar
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    connecting rod end play....the clearance between the two ends of the connecting rod on the same journal

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    1976 Sanger Flattie Running_on_Empty's Avatar
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    rod side clearance

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    hope this helps, rod cheek towards crank cheek with bearing radius to crank radius
    check to see if rods are on right pistons and that your rod and cap are not mixed up

    my book says .010-.012 on steel rod .020-.022 alum rod



    good luck..
    Last edited by flat601; 02-10-2009 at 07:21 PM. Reason: more info

  8. #6
    1976 Sanger Flattie Running_on_Empty's Avatar
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    any ideas of how to increase the gap if everything else is correct

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    Senior Member wagspe208's Avatar
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    Quote Originally Posted by Running_on_Empty View Post
    any ideas of how to increase the gap if everything else is correct
    Put them in a lathe and turn one side down. Of course that assumes you have a lathe. If one was to go thast route, one would want to make all the rods the same, so future matching would be easier. Then, well....some would worry about the balance.
    Stock rods I assume?
    Run it.
    Wags
    Check bearings first as posted.
    Run it. If you are not going to turn 8000 it will be fine.

  10. #8
    1976 Sanger Flattie Running_on_Empty's Avatar
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    there is a slight bind every 360 degrees of rotation....

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    Senior Member wagspe208's Avatar
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    Quote Originally Posted by Running_on_Empty View Post
    there is a slight bind every 360 degrees of rotation....
    Whoa....define slight. Because of ring drag? Rods still free to move the .008 to .011 back and forth?
    Wags
    Now, problem has to be found. Was the crank ground? New? Specs? Rod big end bore? Clearance? Did crank bind without rods on it?

  12. #10
    1976 Sanger Flattie Running_on_Empty's Avatar
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    gen 4 bbc
    4.320 bore (.070) over
    4.250 crank
    displacement 498
    Keith Black hyperutechtic pistons
    top ring - .0345
    2nd - .016
    oil rings - .016
    6.385 rods

    all brand new parts....balanced...naturally aspirated

    crank rotated fine
    installed piston and rods and there was a slight drag every 360 degrees

  13. #11
    1976 Sanger Flattie Running_on_Empty's Avatar
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    it will spin all the way around it just seems to be a little tight at one spot in the rotation

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    Senior Member wagspe208's Avatar
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    Quote Originally Posted by Running_on_Empty View Post
    gen 4 bbc
    4.320 bore (.070) over
    4.250 crank
    displacement 498
    Keith Black hyperutechtic pistons
    top ring - .0345
    2nd - .016
    oil rings - .016
    6.385 rods

    all brand new parts....balanced...naturally aspirated

    crank rotated fine
    installed piston and rods and there was a slight drag every 360 degrees
    Did you rotate the engine to check for drag every time you installed a piston/ rod combo?
    What piston is at the top of the bore? I assume it is a certain spot always.
    Are these pressed on pistons? Were they all free if so? Meaning piston rocked easily on the rod..very easily.
    Wags
    How are you turning it over? Do you have a breaker bar on a crank socket? Bolt on the end?
    Last edited by wagspe208; 02-10-2009 at 07:41 PM.

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    1976 Sanger Flattie Running_on_Empty's Avatar
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    free float...move very easily
    breaker bar on bolt
    seemes to be a drag just before tdc on 1

  16. #14
    gn7
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    Is this a forged crank? Take a rod cap off and look to see if the bearings are either chafered or narrowed. I don't think your rods are seating against the crank cheek, the bearing is edge riding on the fillet. If the bearings are narrowed of chafered they will say upper or lower, some may only have a "U" or "L" on the back side. If they don't, and you have a forged crank, there's your problem. AND MAKE ABSOLUTLY CERTAIN THAT THE CHAFERED SIDE OF THE ROD FACES THE CRANK COUNTERWEIGHT AND NOT THE OTHER ROD!!!!!!!



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    Last edited by gn7; 02-11-2009 at 07:53 AM.

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