Is there any practical reason why the 4th main bearing couldn't be a pressed in bronze sleeve, i.e. SAE 660 bearing bronze instead of babbitt?
My engine has new main babbit, a floating transmission shaft and a freshly aligned pan (Thanks Erik in Auburn!). I just don't see why bronze couldn't be used.......but I've also been divorced twice, so my judgement isn't always good.
Disadvantage is bearing bronze isn't as soft like Babbitt. Babbitt is able to embed particles that otherwise can grind and score.
Your crankshaft rides on Babbitt, the tail shaft IMO should ride on Babbitt too. Ford way.
There's a sealed ball bearing ball cap available from most of the usual places.
The main reason is; The center of the hole in the Babbitt is not necessarily the center of the 4th main housing but is centered to the machined ring on the engine side. If you look at the engine side of a 4th main you will see a machined ring around the cup behind the flange.
This machined ring may or may not be centered with the tube part the Babbitt is pored into. Meaning when the Babbitt is pored and bored it may not be centered in the tube so the hole might be off center to the tube.
My 21' Roadster has a bronze 4th main. Recently, the engine was pulled to rebuild the transmission... and stuff. Out of all the transmission parts, the only parts that were reused, were the output shaft/drive plate and the 4th main. The clearance was still "in spec." after 25K miles. I think my Touting has bronze too. God only knows how many miles are on that car... lots.
As Mark points out however, the bronze, (or babbitt), must be machined concentric with the pilot diameter of the 4th main cup. So, if you use a 660 bronze bushing, get one with an undersized I.D. and machine it to fit your output shaft & also to be concentric.
Jerry good point. Lots of things ride in bronze bearings. Some at higher speeds with less lubrication.
When Herm was active on the forum, he s##t canned the whole idea of a bronze 4th bearing saying it would never work. But in saying that I've come across 2 in the years of re-building T engines and trans, one was completely flogged out and one had been in for more than 30 years and fine, back in it went.
Thanks for all the input guys. I think I'll try it when I get to that point. A good press fit, followed by boring to spec. along with the oil hole in the right place.
The reason I bring it up is that I've put bronze bearings in many things over the years, and with proper lubrication they work well and serve longer than babbitt. They are particularly suited to the shaft speeds of a T.
As for babbit allowing dirt to "embed" well, yes it does. But I intend to keep my oil clean, clean, clean! (A Ford Faithful oiler is planned as well)
I have a couple bronze 4th mains hanging on nails. They work fine IF everything is straight. Crank, tranny, pan. If not and there is too much run out have seen multiple cranks break.
If you want one will box up and sell cheap.
I used the ball bearing kit available from the parts suppliers. Went in without modification to the tail shaft but I had to cut a little off the ball housing so that it would not hit the bearing at the extreme end of travel of the rear end. The kit includes a seal so no oil will leak into the universal joint or rear end, as long as you remember to install the little disk in the center of the tail shaft and use some gasket seal.