1937 248 Rear Main Bearing

[dayz239]

I am rebuilding my 1937 248 engine. I have purchased a set of later year 248 main bearings that are .020 undersize to fit my reground crankshaft. All these new main bearings fit my block perfectly except the rear main. It is about .250 shorter in length. With minimal modification to the locking detents in the block, it will fit right in. By using this complete set of bearings, I know that they all are in true alignment to one another.I have had them all but the new rear main mounted in the block with the crakshaft in place. and all clearences are withinin spec. and the crank turns freely and easily.If I take my original rear main shell and get it rebabbited and then bored to .020 under I am wondering if it will be in true relationship to the others in this new set of bearings I would like to use. The problem with the original rear main is there is no way to line bore it to the other bearings because the other main bearing journal sizes are different( smaller than the rear main )so there is no way to run a line bore through the all the crankshaft bearings to bore them true to one another. By using the available bearing set with the smaller length rear main this problem does not present itself. Has anyone else out there ever used these later main bearings in the 1937 248, instead of doing it the old fashioned way of rebabbiting the original shells, boring them idividually for the different size journals and scraping them in? Any ideas and feedback on this subject would be greatly appreciated

[BigRivy]

If the only difference is that the bearing insert is shorter by .250 I wouldn't worry about it. The engineers decided that they didn't need the extra length in later years so I don't think it will be a problem. The rear journal on the straight 8 is a mile wide by comparison to todays engines. There will still be way more than enough load carrying capacity on the shorter bearing. Make sure that the modifications to make the new rear shell fit will keep the oil groove in the bearing shell and the oil hole in the crank in alignment. As far as your other ideas, I don't know of anybody that rebabbitts old bearing shells. I think you are confusing poured babbitt mains with insert style mains. Two totally different set ups. A lot of what you are referring to in your post has to do with the poured babbitt and was made obsolete by insert style bearings. If you could re manufacture your existing shell to .020 under then yes it would fit fine. The babbitt on most bearing shells is just a thin facing layer. There is a lot more to bearings than babbitt. Research tri metal bearings and their construction. As far as align boring goes the fact that the journals are differing sizes makes no difference. once you establish your crankshaft centerline you can bore any main saddle, insert, or poured babbitt to any size you desire. How do you think that they manufactured the block in the first place? The tool is reset for every main saddle, not run the complete length of the block. You didn't mention if you trial fitted the rear shell with the rest of them. I'd put them all in and if they clearance fine and the crank spins fine and oil hole alignment is fine I'd use it and forget all the other stuff. Keep it simple. Good luck.

[jim.ketchum]

You can not use the later bearing in your 1937 engine. If you look at your old bearing you can see grooves and a hole. These grooves make the oil go to the hole and drain back into the oil pan. The 1937 engine does not use a rear main seal. If you use the later bearing your engine will leak. Egge Machine (800)866-3443 has one of these bearings in stock .020.