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Babbitt main bearings


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I enjoyed the commentary on babbitted vs. inserted rod bearings. What about main bearings? Are repoured modern babbitt mains vulnerable to pounding out, like babbitt rod bearings are? Specifically, I have a '35 Auburn 8 with inserted rods and repoured mains, as we couldn't find inserts to fit the mains.

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I will take the bait and put my vote in for rebabbiting the mains as a very viable practice for your Auburn. I am buckled in ready to take the scud from my Packard counterpart.<P>The Pierce 8 cylinder engines have thick bronze mains which can be rebabbitted and align bored. This works terrific- and I speak from experience on several 8 cylinder engines with thousands of trouble free miles. My friend that does the pouring and machining has done at least 15 Pierce engines and I dont believe that a single bearing has failed-!!! <P>I decided to back out of the last string of opinions (with a few facts intermingled). There is really no debate about the best material for the bearing surface, as most all inserts also use a babbit overlay. Babbit has moderate strength, great embedability, resistance to scoring and resistance to corrosion. It is great for journal bearings. Using the wrong alloy, using the wrong tinning process, using the wrong bearing thickness all yield the same results- which lead people to speculate on alternate solutions, sometimes successful, sometimes not.<P>I think that a big advantage to rebabbiting the mains, or rebabbiting main inserts (only if they are very thick wall), is that you can align bore the block. With a retrofit to conventional inserts, there is zero chance of align boring. Your babbit is only .002-.003" thick on the inserts!! Once you go through that, you are on your way to a siezed bearing.<P>This align boring is particularly critical on engines with aluminum crankcases with bolt on cylinders. These crankcases can and will distort which will misalign the main bores. You MUST have your cylinders bolted to the crankcase when the align boring is done.<P>The other challenge that one would face with trying to retrofit inserts into a block with poured mains would be dealing with the thrust loading. One or more of the mains must carry the thrust loading from the clutch.<P>As a final note, - rather than send you looking for some SAE paper which wouldnt seem to relate to this topic anyway, for those interested, check out the book "The Internal Combustion Engine- In Theory and Practice Volume 2" by CF Taylor MIT Press. It has a great section on bearings, bearing materials etc. I have been a member of SAE for over 20 years and havent seen too many articles which I see applicable to pre war cars.<P>Good Luck with your Auburn. I had a 1929 8-90 Convertible Sedan! It was a great car. <P>Greg wink.gif" border="0

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I agree with the previous posters. At approx 250,000 miles I had to rebuild my 1930 Pontiac engine. I was impossible to find new shells for my main brgs. I had them re babbitted and align bored. I now have 470,000 meles on it and have never had a problem. I used 10 weight oil for about fifty thousand miles and then switched to 20 weight. I change the oil every three thousand miles and the filter (bypass type) every second oil change. I was averaging nearly a thousnd miles a month (untill my differential pinion shed it teeth about eight months ago). On the highway I always drove around 55 mph and with my rrear end and tires what made the engine run about 2800 rpm which is about 1000 rpm above the optimum of 1200 ft/min piston travel. I had absolutely no trouble with the brgs.<BR>Happy hobbying

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Yes...as to MAIN bearings...of course I agree. I have never heard of anyone having trouble with PROPERLY re-babbited MAIN bearing shells operating with CORRECT clearances. Whole different set of dynamics than the brutal operating enviornment of a connecting rod "big end"...........they will work just fine !<P>Pete Hartmann<BR>Big Springs, Arizona<P>'36 American La France V-12 800 cu in.<BR>'38 Packard V-12 473 cu in.<P>Both engines have been PROPERLY over-hauled using conventional over-haul/shop practices....and I have beaten the crap out of both ever since ( a few years ago, I drove the La France to New York and back...at sustained extreme speeds...in AUGUST !

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All,<BR>This may sound dumb but would anyone of you have pic's of babbit bearings. I know what bearings look like for a modern days engine but was curious what a babbit bearing looks like. As you can tell I have never had to do a rebuild on a older engine as of yet.<P>Thanks<BR>Tom Malas

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Tom,<P>I don't have any pictures handy, but they look similar to bearings in a modern engine, but are thicker and non removable. They are poured in place using molds a little undersized. The caps are then attached with shims in between. Then they align bore the block to the correct clearance for the crank. As the babbitt wears, you can remove a shim and tighten up the engine.<P>If I run across any photos or links, I will post them.<P>Hey. look what I found. No real good photos of the bearings themselves, but good photos of the process.<BR> <A HREF="http://users.michiana.org/rosss/modela.html" TARGET=_blank>http://users.michiana.org/rosss/modela.html</A><p>[ 06-14-2002: Message edited by: MODEL A HAL ]

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Model A Hal,<P>Thanks that what I was looking for to see how that process was done. I figured there would of have been some kind of form to poor the material in.<P>Tom<BR>1931 833 Packard

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