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  • July 1, 2011 12:29 a.m. fasted58 HalfDork

    Assembling a '91 4.3L V6 Chevy street performance engine. Stock crank polished, several small journal grooves, crank Mic'd in spec so using Std. size bearings. Engine had 55K on it before 0.030 flat top rebuild.

    Was just going to install Clevite tri-metal bearings but been reading up on bi-metal bearings in forums and mfg. sites. The greatest benefit I see w/ bi-metal bearings would be their 'polishing effect' on this older crank but while giving up the embedability of tri-metal.

    My old school engine machinist says tri-metal.

    What says GRMers

  • Zomby woof

    July 1, 2011 12:39 a.m. Zomby woof SuperDork

    Won't matter. Use what's available.

  • GregW

    July 1, 2011 6:26 a.m. GregW New Reader

    Listen to the machinest. Tri metal will allow the crud that hides in old engines to get out of the way.

  • foxtrapper

    July 1, 2011 7:01 a.m. foxtrapper SuperDork

    If I actually had the choice, I'd chose tri-metal. Many times, you just have to run what you can get.

    If the engine is built properly, and you maintain it properly, you wouldn't run into any bearing problems for a long long time anyways. Regardless of the bearing selection.

  • erohslc

    July 2, 2011 3:33 p.m. erohslc Reader

    If the bearing is touching the journal then you have problems, and bi or tri will not make any difference.

  • July 2, 2011 7:54 p.m. ncjay Reader

    I am curious as to how any engine bearing can have a "polishing effect" on a crankshaft that has already been polished, ar any crank at all. Bearings shouldn't be touching the crank, and if they do, polishing it is not what would happen, more like scuffing.

  • July 2, 2011 9:00 p.m. fasted58 HalfDork

    http://www.summitracing.com/parts/SLP-5085MA/

    "These Sealed Power MA Series main bearings can actually polish the journals on your crankshaft. That's because there's a small percentage of silicon mixed in with the aluminum and tin that make up the bearing-surface alloy. The silicon is there for wear resistance, but its toughness actually smoothes the journals of a crank whose surface hasn't been optimized! This special surface alloy is laid over a high-strength 1010 steel backing and delivers improved seizure and corrosion resistance, as well as better control of wall variance. It also helps to minimize debris embedding, which can score the crank's surface."

    Bimetal bearings are new to me, I've always relied on trimetal.... but after reading this I had to wonder if it would help an older crank w/ several small minor grooves.... hence my original post.

    Like many others here (see the recent Summit love fest post) I've relied on and trusted Summit for over 25 years w/ no regrets or discrepancies.... should I doubt them now?

    BTW, those were their words, not mine.

  • KATYB

    July 2, 2011 10:08 p.m. KATYB HalfDork

    go with trimetal!!!! bimetal are oem bearings or great for all new they are also more brittle and if tolerances are not realy tight are more prone to failure or through abuse more prone to failure. get some clevite 77's and be happy.

  • July 2, 2011 11:33 p.m. fasted58 HalfDork

    KATYB wrote:

    go with trimetal!!!! bimetal are oem bearings or great for all new they are also more brittle and if tolerances are not realy tight are more prone to failure or through abuse more prone to failure. get some clevite 77's and be happy.

    Yup, trimetal it will be, made my mind up last night. It wasn't broke so no use fixin' it... the original factory trimetal brgs did their job and were normal for 55K.

    Did some more research on bimetal brgs. While there are certain advantages for their use in specific hi-perf situations I can't help but get the feeling that one reason for the switch to bimetal by OEMs is purely the elimination of lead from mfging and the environment.

    My engine machine shop buddy said he's been sending out tons of later model cranks to be welded up / reground... gotta wonder if these weren't bimetal bearing cranks as these bearings won't embed like trimetal, so the crank takes the hit.

 
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