Hi, anyone know where I might locate a 3912034 .009 undersize main bearing set or a 3911011 shim kit for my 66-327 mid year? Much thanks.
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Re: main bearings or shims
Mike-----
GM main bearings are not sold by the "set" as are many aftermarket bearings. They are sold as a "kit" which includes the upper and lower bearing half for 1 journal. The same is true for connecting rod bearings.
GM #3912034 was the .009 undersize kit for the REAR MAIN BEARING. Assuming that all of your journals are of the same undersize, you will also need 4 each of GM #3912037 for main bearings 1 through 4. Both of these part numbers are long-since GM discontinued and, unfortunately, the .009" US was not replaced with any supercessive part number. While you might be able to find one or two here and there, it's unlikely you'll find the 5 seperate pieces that you need.
The above-referenced bearings were GM Moraine-400 premium aluminum material. In my opinion, they were the finest for bearings for a STREET engine that were ever produced. But, they are no longer produced.
Most GM main bearings for early small blocks, with the exception of this particular undersize, are available under replacement part numbers. These replacements premium aluminum, are manufactured by Federal-Mogul and are, in my opinion, the next best thing for a street engine. You can purchase the Federal-Mogul bearings from many aftermarket sources and you can obtain them as a set. Purchased through aftermarket sources, they are a lot less expensive than through GM. From what I have been able to discern, the GM bearings and the aftermarket Federal-Mogul are the same except that the GM have "GM" stamped upon them (as well as the "F-M" identifying mark). Check with an automotive engine bearing supplier and you may even be able to obtain the undersize that you need. Just because GM no longer carries them does not mean that Federal-Mogul does not manufacture and market them.
As far as the shims go, the same thing is true, as above. Kit GM #3911011 is a shim kit for the REAR MAIN bearing only. For the other 4 positions, you'll need kit GM #3911010. And, you will need, perhaps, several of these kits. All are discontinued, although, once again, you can likely obtain the exact same thing from aftermarket sources. I don't like the use of shims, though.In Appreciation of John Hinckley -
Re: main bearings or shims
i have never seen .009 under bearing in the aftermarket only .010 under. GM used a lot of special size bearing to fit the cranks that were never sold in the aftermarket. i would take the block and crank to a good auto machine shop and have them check the line bore and the crank journals for size and see what they reccomend. the shims are not a good idea even if GM used them as a crutch to save blocks.Comment
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Re: main bearings or shims
thanks Joe and Clem for your help about the bearings.Comment
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