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Walt Fricke's Avatar
 
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#8 bearing sleeving

Does anyone know what metal is used in the #8 (nose) bearing? Given the cost of replacements for this big piece, I wonder if a guy who does his own machine work could fabricate inserts, machine the bearing ID, and heat shrink them in. If the inserts had lips and the bearing has an additional cut made for the lip, they ought to stay in place - there is very little axial movement, and that only produces a minimal friction load axially. It is some sort of non-ferrous metal, looks like aluminum, but alu comes in all sorts of flavors.

I checked the three I have for the 9 bolt crank engines and earlier, and all have IDs above the wear limit.

Probably has a machining cost making it uneconomical to have a shop, machine or engine, do this. But for the rest of us, if we can have use of a lathe, seems right up our frugal alley. But should be the right - or at least an appropriate - material.
Old 01-27-2018, 01:49 PM
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Sounds like you have a plan. I don't think it much matters what the original bearing is made of, probably some babbett type alloy.

At any rate, I wonder if there is an off the shelf bearing that would work as an insert. A cam bearing from a small V-8 maybe?

If I was going to do it, I would find a piece of brass pipe or tubing appropriately sized. Machine it and the OE piece to rough size and press it in. Finish machining, then have the brass insert coated with something appropriate for a bearing.
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Old 01-28-2018, 09:36 AM
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Walt, I was told 35 or more years ago that #8 shows near no wear because it’s under such oil flow.
This was discussed with a long, now retired, Porsche machinist.
I think you should check the crank for straightness, or runout.
Bruce
Old 01-28-2018, 11:13 AM
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And the bearing is like $175 if it needs to be replaced. How can you make a sleeve cheaper than that and sell it, I don't know. And I am in the business of selling parts.
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Old 01-28-2018, 11:41 AM
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Bruce - that's of course what I thought, though I don't recall reading of oil flow as the reason. About all is supports are IS gear loads (symmetrical and offsetting due to the boxer architecture?), the distributor (has to be negligible), and the fan/alternator (too much belt tension might bias this?). But nothing like the regular mains.

However, a quick check with a caliper (I could get out the bore and snap gauges to be a bit more accurate) showed a bore of 31.115mm (actually 1.225" on the gauge I used) on each.

Here is what the spec book (Wayne copied this into his book)says. It seems to show a wear limit for the crank, but for the bearing just says "inspect." Rod and regular main bearings don't get a wear limit spec, it seems, which makes sense - "while in there, why not replace" as they are a wear item.



I may be misreading these specs - They are for the SC, not the 2.7 crank, but the ID/crank od specs are the same. I take the top of the given range of 31.084 as being the limit. The wear limit a line down has to be for the crank at d3. But I suppose I could take the +0.048 into account? Measure the crank (the one I just had checked and cleaned etc. was within spec, though at the narrow end, which should be fine for a race motor - and straight, too, though it never saw the three #8s I just checked)and the bearing ID and see if within 0.048mm?

However, the bearing surfaces of all three feel rougher than, say, the OD. I don't think anything this large is made of Babbit metal. That's just a coating over something else and then steel for regular bearings, and used for its embeddability. Aluminum of some flavor is adequate as a bearing surface for some level of loading - the sand cast cases had no IS bearing inserts at all, and you don't - at least I haven't, though I am far from the best eye for this kind of stuff, on my several sand cast cases - see wear on that surface.

Anyway, there is no need to use a "real" bearing or bearing material, and you don't find many bearings which aren't split, do you? Adapting a split bearing - and actually two of them - to fit inside a tube wouldn't work, as they need crush etc. Or would involve a split carrier, which was then inserted. Much more work than what I am imagining.

As to flow, the #8 supplies half of the rod bearings (not so many if you have added center journal rod bearing flow). It has me wondering if the surprisingly low pressures I saw on my SS2.8 (before a piston pulled in half, unrelated to oil issues) might have been related in some way to this. This experience led to a long discussion here about oil pump specs, which has a lot of helpful stuff generally. So I'd think excess clearance here could be problematic.

It would be interesting if guys with #8s sitting around on their shelves were to measure IDs on some and share. Including if anyone has a brand new one.

I think it still would be good to know what flavor of aluminum these are made of, though. Or whether for this application it really doesn't matter, you don't need T6 or something, and so on, and just about any ordinary bar stock of appropriate OD would work?
Old 01-28-2018, 12:06 PM
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Are you talking about putting the nose bearing in a lathe, and removing the material to fit a sleeve in, plus making the sleeve itself to press in?

My only reservation is keeping everything concentric. But, it should be straight forward.
Old 01-28-2018, 12:57 PM
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Tippy - that's just what I had in mind. Maybe adding a ridge (so it presses or heat shrinks in only to the right depth) is superfluous?

Catorce - I'm not in the business. Pelican shows this bearing from Porsche at $429, and others at $240 and $219. One of these less expensive aftermarket bearings has two glowing reviews other than a quibble about the depth of the locating pin hole. I don't know how guys in the engine building feel about these non-Porsche bearings, though it doesn't look like a complicated part to me (though I'd not think of making my own from scratch).

12" of 2.5" 2024 bar stock is $73 plus shipping from Grainger.

So far, though, no suggestions on what the right material is.
Old 01-28-2018, 01:26 PM
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Oh, I guess that concentricity could be dealt with by making the ID of the sleeve undersized, and then reboring or honing to size after it was pressed in? Like valve guides?

If the insert impinged on the two oil drain back holes, maybe that would be OK if maybe half of the circle were left open? Those are plenty big, one would think, to avoid excess pressure on the nose bearing seal.

And 1.75" bar stock would be better and cost less - 2.5" is about the OD of the whole bearing.

All this might well cost more than $200 for a commercial operation - send in your bearing and get it back = postage. Machinist time (and I don't suppose a guy with a CNC mill is apt to charge less? got to pay for the machine)? Handling time. The bar stock would appear to be the least of the costs. But for a DIY guy, saving $100 plus making something has its own values.
Old 01-28-2018, 01:37 PM
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https://en.wikipedia.org/wiki/Babbitt_(alloy)

https://www.rotometals.com/babbitt-bearing-grade-3-super-tough-alloy-ingot/?gclid=EAIaIQobChMIt8iDgOz72AIVG7XACh1EkAQ_EAQYASA BEgIHqfD_BwE

https://www.summitracing.com/parts/cle-sh506s?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-clevite-engine-parts&gclid=EAIaIQobChMIhru-vvP72AIVyrbACh2CGAruEAQYBSABEgIAS_D_BwE
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Last edited by Trackrash; 01-28-2018 at 03:23 PM..
Old 01-28-2018, 02:50 PM
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Gordon - so someone does make full circle babbit faced bearings. Finding IDs for Clevite/Mahle circular cam bearings is a chore, as it seems typically only the OD is speced - you purchase for the specific Detroit iron engine, with its set cam ID. The snout of the 911 cam is about an inch and a quarter in diameter (bit less), and I think only maybe a Briggs and Stratton one cylinder lawn mower cam might have a base circle that small. But there might be other options. For instance, maybe an Ooilite bronze impregnated bearing, turned a bit to get it just right OD and ID? But is that better than the aluminum surface of the stock bearing, or even as good?
Old 01-28-2018, 07:45 PM
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https://www.mcmaster.com/#babbitt-bearings/=1bbzeax

If you could get just the bearing, in 1 3/16" ID, I think you would be in business.
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Old 01-28-2018, 08:31 PM
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Hmmm might try it on some old nose bearings? It is an important to oil flow, if you loose oil at this bearing one end of the crank doesn't get fed...sleeve it and hone to size should be pretty easy.
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Old 01-29-2018, 09:04 AM
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