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Thread: Has anyone had an success re-using a crankshaft thats' spun a bearing?

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    Forum User Feedback Score 0 Roy's Avatar
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    Has anyone had an success re-using a crankshaft thats' spun a bearing?

    I've never re-built one of these engines, and its been quite a while since I've read a thread about this on that other site about these cars.

    So, has anyone spun a bearing, gotten their crank turned, and re-used it without spinning another bearing shortly after?

    I tore apart a spare motor tonight so I can start building it for my single turbo car. I'll buy a new crank if I have to, but I'd rather not make a table lamp out of this crank if it can be re-used.

    This is the bearing with the most damage:




    EDIT: Damn beer, made a typo in the title and I can't edit it. herp derp derp.
    Last edited by Roy; 02-06-2011 at 01:27 AM.
    1992 Mitsubishi 3000GT VR4 - Single Turbo - http://roycormier.net

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    afaik, it's been done numerous times. it should be entirely safe assuming it's reworked properly.

    fysa, i'm offering nitriding & cryo-treating for forged cranks. $250 & it includes return shipping.

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    Is that a cast crank?

    Trouble with a spun crank is it will need to be turned. You will have to remove the oil galley plugs out of the crank to properly and thoroughly clean both the spun bearing material and the crank turning material. And if it's cast it ain't worth it any way.

    Personally I never re use a spun bearing crank. Not worth the trouble.

    -Chris

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    LW fears my posts Not Verified Feedback Score 1 (100%)
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    I've done it with my old turbo Eclipse. That car however was a daily driver, hardly any mods at all. It was still going strong 30k+ miles after I rebuilt it. I haven't done it with a 6g72, but I don't see why it wouldn't work either.

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    Forum User Feedback Score 0 Roy's Avatar
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    Its' forged, but that does sound like quite a bit of work.

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    Quote Originally Posted by Roy View Post
    Its' forged, but that does sound like quite a bit of work.
    The forged TT cranks are nitride hardened and turning the crank will remove it. The service Imperfect is offering should make the crank even better than new at a much lower cost. Just be sure the crank is straight (or can be straightened) before it is treated. It's also a good idea to turn the crank to .005" bigger than finish size before nitriding, then do the final grind/polish after treatment. I've got two 16G motors at 600+ AWHP with cranks treated just that way and I know of 3 others and no one has had a problem. The key is making sure everything is clean and blue printed during the rebuild.

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    If you take material off the crank make sure you get the bearing clearances correct. And don't just use plastigauge. It is too vague. Use mics and bore gauges.
    .0020"-.0015" is good for the rods.
    .0025" is fine for mild builds on the mains. If making big power I suggest .0020

    If rods are too large it's simple and pretty cheap for a "good" machine shop to resize the rods. They will cut the cap down, torque to the rod, and re hone to size.
    If the mains are too large you will need a line bore which is expensive.

    If you have more than one set of bearing measure them all, even mix halves as that may help you get in the spec you want.

    If you have more than one block, read the block stamps that tell you what size the mains are, and read the crank size. Sometimes you can mix and match to tighten it up.

    I had a mix of good parts for the last rebuild I did on my car and I mixed my largest used forged crank (polished) with my smallest block (clearances stamped on block) and got the mains to .0020". Had the rods resized to .0018"-0020"

    -Chris
    Last edited by Ninja Performance; 02-06-2011 at 10:43 PM. Reason: spelling

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    Well thanks for the replies, lots of good info...

    Right now I'm trying to decide between rebuilding the 6g72 with better internals, or doing some sort of stroker. The block is a 2-bolt so I'd probably try to find a 4-bolt block if I don't go for a stroker. Then I just have to figure out what to do with the heads, I've heard of the headlift fix where some passages are welded up, or also o-ringing the heads. Though I was told the heads would have to be re-torqued often if I got them o-ringed, so that doesn't sound like something I'd want to do.

    Quote Originally Posted by inperfectdarkness View Post
    fysa, i'm offering nitriding & cryo-treating for forged cranks. $250 & it includes return shipping.
    I might have to talk to you about that if this is the route I decide to go.

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    imho, keep the 2-bolt block UNLESS you go for a stroker. the limits of the 2-bolt are established; they're north of 800awhp. and even then, you can get a stud kit to fix the issue. if your goals are anywhere <700awhp, you're not at risk at all by sticking to a 2-bolt. hell, 99%+ of these cars are running less than 700awhp; so that's kinda saying something.

    personally, i would have probably kept my 2-bolt block if i was going for a 3.0L build.

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    Would a 2-bolt block with different studs be able to handle 1000AWHP? My turbo and fuel system will be able to handle it, so I'd like to build a motor that can as well.

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