Hey guys, tonight I took apart a 383 that I bought after the thrust bearing got munched because of a balloned converter. The short block itself only has 2000 miles since the last rebuild. The crank is cast steel and has been turned .010" on the mains, and 0.020" on the rods. All the bearings in this motor are Clevite 77 "P" bearings. The crank has ZERO markings or scoring.

Anyway, every single rod bearing cap has a spot in the center of the bearing where the copper layer can be seen. The rod side of the bearing doesn't have the copper showing on any of them. Then I moved on to the main caps and the cap side of the bearings have the same condition, but not the engine side of the bearings.

Since the thrust bearing was toast and I needed to teardown the short block to replace the thrust bearing anyway, I bought a whole new set of both main and rod bearings instead of reusing the ones already in it. So they are all being replaced anyway, that isn't the issue.

I am just wondering what would cause this? I was thinking it is the bearing material shed from the thrust bearing that might of caused it because of it being in the oil before the problem was noticed.

I am wide open to ideas. Thanks in advance guys!!

Running into detonation would be a factor. Any chance of that?

Jim

Detonation would have hammered the high side of the bearing, i.e., the half set in the rod itself. Check your rod side clerances and make sure there's at least .015". Hopefully one of the machinists here can shed some more light. I'm thinking theres a clearance off here.

There are a lot of things that can cause it. Too much clearance, oiling system problems, improperly sized, or out of round rods. Detonation, at least on the mains. I would think that if it was bearing material from the thrust, you would see marks around the entire bearing, not just half. Hard to tell exactly what to look for. Just check and double check everything before assembling again.

Look at the back of the shells. Have they been moving? (Shiney spots) Do they 'snap' into place? Would indicate rod / main bore sizes out of tolerance, like Bill said.

Cable,
I think you can rule out detonation. As Gene said, detonation would have shown up on the rod shell instead of the cap shell. Check your clearances very carefully, as I suspect this may be the problem.
Also, the top layer of Clevite 77 bearings is a very thin flash coat of tin/lead for lubricity. This layer should show a wear pattern on the center of each shell, which covers 2/3 to 3/4 of the bearing surface. This wear pattern should be consistant across the bearing shell.
In order for the copper to be showing, the tin/lead layer, as well as the Babbitt and the Nickle 'dam' would have to be worn through. Odd that this wear is showing up only on one side of the bearing. Check the concentricity of the case and the rods, with the fasteners torqued, then recheck with the bearings in place.

Originally posted by engineguy:
Check your clearances very carefully, as I suspect this may be the problem.I am guessing you mean the clearences were too tight? I planned on polishing the crank on the rod bearing surface before reinstallation. If you mean the clearences were too loose, should I run a 0.021" bearing instead of 0.20"?

Thanks for the help guys.


Another thought, after the thrust bearing was wasted the crank was able to "walk" quite a bit. Before the teardown I took a feelergauge and measured the thrust clearence at 0.030". If I remember correctly, 0.010" is suppost to be the max. Would the crank "walking" cause problems like this with the rod cap bearings?

Also, could this be a problem of everything not being torqued down enough or too much? I didn't assemble the motor the last time, a shop in Bakersfield did the short block work.

Cable,
Actually, too much clearance will usually cause the problem you are describing, with the wear in the "center" of the bearing.
The following statement really scares me: "I planned on polishing the crank on the rod bearing surface before reinstallation." Unless you have the proper equipment to do this without getting the crankshaft out of round, or tapered, you would be better off to leave it alone. If it needs polishing, have someone do it that grinds crankshafts. There are polishing belts available that do not really remove any metal, but they are meant to be machine driven. I have seen too many crankshafts ruined by a home polishing job.
Here is a good link to look at, I am surprised that Engineguy Bill did not recommend it smile.gif
http://www.clevite77.com/Motorhead/techstuff/bearings.html

Originally posted by BillK:
Cable,

The following statement really scares me: "I planned on polishing the crank on the rod bearing surface before reinstallation."No worries, I didn't mean myself personally doing the polishing.