I know this is an old topic, but just wanted to throw in my 2c.
When I was running Model A's with Babbitt bearings, I made the mistake one time of getting one too tight. I was on a date heading to a show, when about 10 miles into the trip, a rod bearing melted out. Fortunately a buddy was behind me heading to the same place and picked us up.
Jerry's thing about tinning the iron so the babbitt wouldn't spin out was taken care of on the Model A Ford with a few blind holes drilled into the block and cap to lock the poured material in place. I knocked the worn out Babbitt out of one engine and didn't find any evidence that the block had been tinned at all, just pegs of bearing material where it had flowed into those holes. I had one engine redone at a shop in Fresno, probably long gone by now, as that was back in the late '60s.
Done properly, a Babbitt job can last a long time, removing shims to keep the clearances proper (but don't get them too tight). As was mentioned, they will embed pretty large particles and not damage the crank journal enough to require grinding.
I haven't torn into my 216 on the '51, and don't necessarily plan on it. It runs pretty well as far as I can tell, but I haven't put a load on it. We shall see when it comes time to get it on the road again.
