Hi everyone,
I have a 1929 194 engine apart, and the mains and rods have spalling. Sludge in the pan was high enough to plug up the oil pump screen. I'll say that's cause and effect. There were lots of particles embedded in the main bearings. Looks like a teenager's paint job, real heavy on the flakes. So should I have everything rebabbited as original or machine out the babbit for inserts? I've done that successfully on 216s. Crank looks good, but didn't mic it yet.
Bob ADler

Bob,
The mains are already inserts. They have a thicker coating of babbit than modern bearings. Though you might get "precision" bearings to fit the crank it is by far the best to get them line bored. That way you are sure that they are straight. And straight is more critical in a 3 main bearing engine than the later 4 and 7 main sixes.

The '29-31 rods have the thrust surface formed by machining the babbit. If they are inserted then thrust control becomes a problem. You can use '32 rods that have the thrust as part of the steel rod forging. They can be inserted relatively easily.

I personally have never inserted the rods. Because of the lack of an effective air cleaner, a relatively open crankcase and other means for particulate matter to get into the lubricating system I am a firm believer that the thicker poured (or spun) babbit is better than the hard metal backed thin babbit inserts. Particles that would damage the inserts and crank get buried into the thick soft babbit.

I have not observed the problem of pounding-out soft babbit causing rod or main bearing failure. All failures have been just the opposite. The babbit has become embrittled and fractures or chunks dislodged. I know that this counters the popular viewpoint.

Though I have not driven these babbit pounder 6s as many miles as some others, I do have many thousands of miles behind the wheel of an assortment of years and models. I regularly drive them on tours and may put up to 1000 miles on a given vehicle in a year. I don't baby them but attempt to drive smart and not over rev them or down shift excessively. Either can twist the crank to an extent that the center main is damaged.

Since you cannot significantly change the inherent weakness of the three main engines I would opt for the original bearing configuration and drive them within their limits. But the decision on what to use is up to you.

Chipper probably is right on with this situation, I hadn't given that much thought about the reverse stress on the crankshaft with a lot of down shifting going down hill, but it sounds reasonable, also the pushing in on the clutch and releasing it is a major effect on the thrust end to end on that old crankshaft, at least in my opinion. I also don't like the inserted rods because I don't think that they transfer the heat of friction away from the rod journals as well as poured bearings because of the extra surfaces between the insert and rod.(IMHO)

I believe that the babbited rods are better if your fitting them up to a crankshaft that has not been turned.They give you more to work with as far as fitting (adjusting) goes, both now and in the future.There just more forgiving.

I have a set of NORS standard size mains if you need them. It is unlikely that your crank is good enough to use them, but let me know if you need them.
Mike