Engine: Big end shell spining in rod -------- Why

[compsec]

Had a knock develop on my straight six flathead (Studebaker) got the sump off today and found one of the big end bearing shells had spun in the rod end hence the knock--------------- any ideas why ?

[PackardV8]

Usually a spun bearing was caused by oil film breakdown, which causes the bearing to overheat, which causes the bearing to weld to the crank and spin in the rod. Once a bearing has spun, it often overheats the big end, so it's better to get another rod, have all six resized, have the crank reground and start over.

It would also be a good idea to determine what caused the problem in the first place:
1. Old oil or low oil level.
2. Too much RPM for too long.
3. Coolant overheated
4. Debris in oil
5. Crankshaft worn oval, tapered or flat-spotted.

What did the oil look like and smell like when drained? How long since the last oil change?

jack vines

[starliner62]

I found # 1 rod loose in my son's 58 Commander which had the original 259. If my thinking is correct, number one rod is the last rod to get oil and I heard my son crank the car cold many times and instantly rev the engine. I think he has learned his lesson. The car now has a nice running full-flow 259 that runs 25 degrees cooler than the old engine, uses no oil (yet) and runs so much better than the old power plant. The oil in the old engine always turned black quickly and it used quite a bit, mostly out of the left bank. The gas mileage went from about 16 to almost 20mpg since the swap. I would guess that the old engine had some compression issues as well.