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Thread: Bearing Thickness

  1. #1
    Lead Engineer RWOLFEJR's Avatar
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    Bearing Thickness

    Question...
    Say you are using an aluminum plane or sleeve bearing and it is supported in a cast iron bore... like a engine block... Will changes in the bearing insert thickness make any difference to the load carrying capability? Would a .250" thick insert be any better or worse than an insert that's say .160" thick?

    I'm thinking zero difference in load carrying capablity regardless of thickness but I have somebody telling me otherwise. I'm thinking you either exceed the compressive yeild or you don't, and thickness wouldn't have any effect...? Am I wrong thinking this?

    Any input would be greatly appreciated...
    I need to make a move on this project one way or the other soon. I've been tackeling a little bit of ugly I encountered on my tractor and need to pick a path and run with it. My center crankshaft bearing bore is out of round and I am about to either ream or line bore. I can ream on target with the rig I made up, but a bearing manufacturer that sells .250-ish thick inserts that are proven to work fine... doesn't think going with .160-ish thick is a good idea? Line boring this thing is going to be a royal pain in the butt and add yet more cost to this money pit...

    Thoughts?
    Thanks,
    Bob

  2. #2
    Technical Fellow
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    Bob, Sorry to hear of the plight, but having done my share of jury-rigged projects in my youth, I would toss my hands up and haul it off to be line-bored. Think about it, this is probably the last time in 30-years it will need this. Reaming sounds like a temporary job to me and I hate doing stuff twice+.

    On bearing thickness, my opinion would be to go thinner rather than thicker, thus leaving less material to plastic-flow if that was it's wont at some point. However, if a bearing guy is saying 0.250" then I would go with him especially if he is selling both thicknesses -- and at around the same price. Theory is a start to a journey, experience is a legendary tale!

    Man, that hurts to "think."

  3. #3
    Lead Engineer RWOLFEJR's Avatar
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    Looking through some old TGP drops we have here and some bearings that have been on the shelf for years... The drive from a bore micrometer to add a little accuracy and a cutter and Voila... portable line boring. Just add drill... Store bought are around 2 grand and I'd still need to adapt it. But I'm still leaning toward the adustable ream and then hand mashie the thinner wall aluminum inserts to suit.

    Had a big epistle written up for a reply and decided not to post it cause when I re-read it I sounded like a lazy whiner. "But I don't want to line bore it.... wah... wah... It's gonna be so much more work... wah... wah..."

    I'm gonna NIKE out on this thing this weekend and just do it. Chips will be flying one way or the other. This situation gave me cause to pause, but it's time to make it happen. Worst case I screw things up and hang my head and take it somewhere.

  4. #4
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by RWOLFEJR View Post
    Would a .250" thick insert be any better or worse than an insert that's say .160" thick?

    Thoughts?
    Thanks,
    Bob
    More contact area is usually better - with limitations. If you where asking about a 3" bearing area vs. .160” one could say that more bearing are is still better, however that 3” bushing/bearing would be problematic to install.

    I think a 2:1 length vs diameter tends to work very well..

  5. #5
    Lead Engineer RWOLFEJR's Avatar
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    Hi Kelly,
    I'm sure I wasn't real clear on this but I meant... Two bearings of equal width and diameter but different thicknesses. Say both about 1-7/8" Wide and say a 4-1/2" I.D. but the O.D. or wall thickness varies from 1/4" vs. .160 wall.

    The bearing guy I've been dealing with is more of a machine shop... not an actual bearing house. from 1956 to 1959 Deere made two very similar tractors. Almost identical with exception of some minor details / improvements. the model 820 was 1957-58 and the model 830 was 1958-59. Both tractors used aluminum outer mains with approx. .006 clearance and roughly 1/4" wall thickness. The 820 center main is a laminated steel / bronze / babbit bearing at about .160 wall. The 830 changed to a center main of aluminum to the same dimensions as the outer mains except the width is about 1-7/8 and it's two piece.

    So when the fellow selling these aftermarket aluminum bearings suggested that .160 thick aluminum centers in this might not be good... I was keeping in mind that the "known" is the 830's bearing that are .250-ish. My thoughts are that as long as the load carrying capability of the bearing material being used isn't exceeded then either wall thickness wouldn't matter.

    But... Like Dave mentioned... With more or thicker walled material you could allow for more movement.

    There would also be a slight change in clearance that would be taken up when warmed up. The "hole" wouldn't close up quite as much with the thinner wall thickness aluminum bearing as the thicker aluminum bearing.

    Then there's the original laminated bearings... The book clearance calls out .0015min to ?? something I forget. So I figure I'll need to bump up to more like the .006 like is required on the outer mains.

    I'm just not sure why the fellow making these things had concern about using a thinner walled aluminum suited for my bore? Maybe it was more due to how much stroke he has available in his collet to machine these?

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