Cross Drilled Crank
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Cross Drilled Crank

  1. #1
    Senior Member Constant840's Avatar
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    Default Cross Drilled Crank

    I have heard pros and cons.

    Any opinions here?

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    never herd a negative, you got me curious too, i'm runnin a 4.25 stroke 4340 eagle that's crossdrilled for better oiling

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    It was thought....by many crankshaft companys (mainly Cola)...along with many professional engine builders...that crossdrilling cranks weakened them. So Cola quit doing that.
    Old school builders such as myself (admitted) insisted on cross drilling. So many crank builders continued to give the public what they wanted.

    However...I built a blown alcohol deal with a non cross drilled Cola crank.....and used 3/4 groove main bearings...and she is alive today never having a problem and the bearings look great.
    So there you have it. And Just a note here and then I will shut up. The "How to build a BBC" is not a bible. It is full of falsehoods and mistakes with the biggest one being the superiority of the BBC oiling system.

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    Senior Member Constant840's Avatar
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    I have heard that though they are supposed to oil better, at high RPMs they can have trouble over coming the centerfugial force of the engine and end up not oiling as well.
    Thus a HO oil pump is needed?
    I wonder... is there a specific minimum oil pressure that should be run with these cranks? I have heard 10lbs per 1k prms to overcome the centerfugial force in a regularly drilled crank.
    Last edited by Constant840; 04-25-2008 at 11:06 AM.

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    gn7
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    Quote Originally Posted by Constant840 View Post
    I have heard that though they are supposed to oil better, at high RPMs they can have trouble over coming the centerfugial force of the engine and end up not oiling as well.
    Thus a HO oil pump is needed?
    I wonder... is there a specific minimum oil pressure that should be run with these cranks? I have heard 10lbs per 1k prms to overcome the centerfugial force in a regularly drilled crank.
    You almost had this nailed down, but there is almost no need to over come centrif. force in a non cross drilled crank, if any thing most of the force is helping. On a cross drilled crank at high r's, the oil hole in the main journal, facing the main cap, is not being oil, hole on the other side is. So the oil column in the journal is trying to shoot straight thru to the other side instead of to the rod journal. In a non cross drilled crank, once the oil passes the center line of the crank, centrif is trying to throw to rod journal because it's the only place it can go. And there is some thought thar cx drilled cranks are stronger. Personally, I run 3/4 groove bearings and don't sweat it either way



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    "Personally, I run 3/4 groove bearings and don't sweat it either way."

    Yep.

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    058
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    I wouldn't cross drill a crank even if the company offered it for free....and thats for a Ford with 3" mains and 2.5" rod journals.

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    www.highflowdynamics.com LakesOnly's Avatar
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    Running a main bearing with a groove greater than just the half shell has a very similar (if not the same) effect as cross drilling....without the cross drilling.

    LO
    High Flow Dynamics
    Performance Components for the 429/460 Engine Family


    This post © Copyright 2007-2017 Paul Kane. No copying, linking, printing or otherwise without express written permission.

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    Senior Member Constant840's Avatar
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    Hhhmmm. So many mixed opinions.
    I ask because I have a forged 454/502 cross drilled crank sitting on the shelf.
    This is a GM piece. Would 3/4 groove bearings be a better alternative?

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    By all means run it. I like 3/4 groove bearings regardless. But some guys don't.

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    058
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    Quote Originally Posted by LakesOnly View Post
    Running a main bearing with a groove greater than just the half shell has a very similar (if not the same) effect as cross drilling....without the cross drilling.

    LO
    Not exactly, Paul. A 3/4 groove does not completly lose the hydrodynamic pumping action that the X drilled journal does. The groove still allows for oil to stack up against the end of the groove as the journal rotates. The cross drilled oil hole relys strictly on oil pressure the oil pump provides as there is an exit for the oil that eliminates the pumping action the turning journal makes. Cross drilled cranks are not much different than a full 360 deg groove bearing. It takes more oil pressure to lube the mains and rods with a full groove or x-drilled crank than if the crank was not cross drilled.

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    gn7
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    sorta what I was trying to say earlier, it isn't that cross drilled cranks need more pressure due to centif force, but due to the fact that the force doesn't help feed the rod and does help to shove the oil out the other side of the crank journal, where the force actually helps move the oil thats in the crank along to the rod after the feed has been shut off in a non X crank



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    www.highflowdynamics.com LakesOnly's Avatar
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    Quote Originally Posted by 058 View Post
    Not exactly, Paul. A 3/4 groove does not completly lose the hydrodynamic pumping action that the X drilled journal does. The groove still allows for oil to stack up against the end of the groove as the journal rotates. The cross drilled oil hole relys strictly on oil pressure the oil pump provides as there is an exit for the oil that eliminates the pumping action the turning journal makes. Cross drilled cranks are not much different than a full 360 deg groove bearing. It takes more oil pressure to lube the mains and rods with a full groove or x-drilled crank than if the crank was not cross drilled.
    I do believe we are essentially on the same page 058; allow me to clarify:

    Quote Originally Posted by LakesOnly View Post
    Running a main bearing with a groove greater than just the half shell has a very similar [<---3/4-groove] (if not the same[<---full-groove]) effect as cross drilling....without the cross drilling.

    LO
    High Flow Dynamics
    Performance Components for the 429/460 Engine Family


    This post © Copyright 2007-2017 Paul Kane. No copying, linking, printing or otherwise without express written permission.

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