OK - so it's not enough that I have to worry about the machine work from Crap-O-Motor, now I have to worry about magnetism attracting various bits of killer metal! It seems like it used to be easier than this!
David and Bill -
I've been thinking a lot about this bearing failure situation. I also re-read an ancient Smokey Yunick book and picked up a few tidbits.
Here's my new and improved failure analysis:
It seems that the lousy machine work and resulting rough and uneven bearing bores caused poor contact between the bearings and the bores - thus keeping more heat in the bearings instead of transferring it away. Since I was thrashing the car at the time it went south, the motor was already hot and excessive heat in the rod bearings could easily have started to make the oil wedge thin out. Then, since I was hammering it through an uphill turn and running higher rpms, I believe the oil both stacked up against the side of the pan and built up in the valve covers. This allowed the pickup to suck air for a heartbeat, and the excess heat in the bearings eliminated any margin for error. The result was fried bearings and enough debris to spread the misery around a bit.
So - assuming this is a correct analysis - then this time around:
- I've corrected the machining problem and should have better bearing-to-bore contact - plus the clearances are now on the tighter side so I'll get more consistant bearing crush - improving the contact even more.
- I'm considering swapping in a Milodon performance pan with some baffles to keep the oil in the right part of the pan.
- I'm still unsure about how to keep excessive oil from collecting in the valve covers unless I use restrictors, which I don't think are a good idea on a street motor - any ideas? (I wasn't running either a HV or HP pump - just stock Z-28 with a standard pressure spring)
'69 400SB, Richmond 5-speed