Bearings

[Jeremey]

What causes bearings to spin? I pulled the engine out of the Bird today to find 3 rods with spun bearings. I have an idea as to what happened but would like to hear some other ideas as well.

[WS6 VERT]

Don't confuse a "bad" bearing with a "spun" bearing. A bearing could be shot, yet not spun.
Bearings that have excessive clearance are "bad". Bearings that sieze (or temporarily sieze) and spin inside the component that is supposed to hold it, is considered "spun".

A "bad" bearing can usually be replaced, and the crank journal may be polished or may need to be turned (and undersize bearings used).

A "spun" bearing will require replacement, or re-sizing of the compenent that holds it, since a spinning bearing will wear the hole out larger or out of round. For instance, if you spin a rod bearing, the bearing stuck to the crank and spun inside the connecting rod, and wore the connection rod out. It will need to be resized or replaced.

As for causes, both are caused pretty much the same way, its just that a "spun" bearing is the worse extreme. Usually bearing failures are caused by low/no oil pressure, contamination (i.e. coolant in the oil, or dropped dirt...) and there are other factors too.

[ragtop88]

Detonation can also play havoc on the bearings....

[Jeremey]

The #1,3, and 5 cylinders spun the rod bearing. I know this because when I removed the cap the parting line in the bearing was turned 90 degrees out of position. When I removed the rod I found that it had chewed the lock off of both bearing halves and had spun in the rod. The big end of the rod is all chewed up as well. It scored the bearing journal up pretty badly and wore the side of the rod and crank down. You could twist the piston in its bore quite a bit. This engine has less than 1000 miles on it. All the parts were pretty clean as I thought they would be seeing how I changed the oil every 500 miles. After taking the first piston out I put my click type torque wrench in revese and slowly increased the torque to check what they were tourqed at. The 7 other rods were all torqued at 65 ft-lbs. Shouldnt they have been tourqed to 45? Here is a pic of one bearing half from #1.
http://www.fbody.com/members/b92z28/Mvc-007e.jpg

[ April 30, 2002, 23:26: Message edited by: Jeremey ]

[WS6 VERT]

Yes, the rod caps should have been torqued to 45 ft/lbs, but its hard to say using that method, that they were really origianlly torqued to 65, but it still sounds like it was high.

I'm not sure if the overtorque is what spun the bearings, especially since its on the odd cylinders only.

Is that the ONLY damage? Any main or cam bearings damaged? Is it possible that all the odd cylinders had the rod installed backwards?

[Jeremey]

The mains and cam bearings are in great shape. I did notice that one of the rod caps on a damaged rod was on backwards. I didnt notice the others. And if I remember right it wasnt the rod itself backwards, just the cap.

[WS6 VERT]

:eek: Sounds like its time to start over w/ some new rods. Who put the motor together?

[Jeremey]

A local guy who was known to be good with building race motors. It was after he built mine that I found out that he was hooked on several types of hard drugs. About a month after it was built he lost his business.

[irocbsa]

Man, that's rough. Nothing like finding out your engine guy is on lots of dope. S***, sorry to hear that. :(

[WS6 VERT]

That really sucks. Makes me glad I built my own now. I have probably over 4K miles on it, and it still have the same great oil pressure and no noise as when I first installed it.

[Jeremey]

I am going to assemble the next engine that goes in the bird. I have assemble a few stock engines and didnt have any trouble, but seeing how I knew that engine would be ran hard I decieded to pay someone else to do it. Oh well you live and learn.

By the way 100 POST! yipppppeeeeeeee :cool:

[WS6 VERT]

I have done countless "stock" rebuilds, and this was my first "hi-po" engine buildup. Alot of things are the same (assembly wise), its just that the math isn't laid out for you in a service manual. You need to figure out cam lift vs spring, rocker geometry, compression ratio, etc...