[Dragncar]

Originally Posted by johnta1

Really easy sometimes.



Never had a main spin but when a rod bearing spins it will usually get hot enough to do major damage.

Basically the bearing shell starts sliding under the other shell , if the 'clearance' is on the upper part, that makes the crank closer to the head/deck of block. (wedges the crank up when the bearing goes under the other bearing) I have heard they will squeal a little before they do it?

A 455 I bought from a guy had bearings "stacked" on one journal. Cast rods. I told him not to mess around with cast rods, but he did. Ran 12.20s. Block is great, crank needs checked and ground.
It never seized, shut it off just in time.

[Sirrotica]

FWIW, In almost 50 years or repairing cars, and racing them, I once had a customer bring me a seized 360 AMC V8 in a 79 Wagoneer. Even though he had been warned repeatedly about revving a cold engine, he started it up and revved the crap out of it daily when cold. It finally caught up with him on a winter day, and he spun a rod bearing, and that bearing stalled the engine and locked it solid.

Of all the engines I've spun bearings on myself, and all the customer engines I've worked on, that was the only one I ever saw locked up. Most just destroy the rod/block, crank, and bearings, but continue to run, and don't lock up. The 360 was also a rod bearing, not an main, so if a rod can lock up an engine under just the right circumstances, a main also could under the right circumstances.

The AMC engine only required a crank kit because the engine stopped immediately, the rod was still round. Like the main in the picture it only moved about 1/2 inch. New crank kit, and down the road it went until it rusted out. That is the only engine I've ever repaired with a spun bearing that didn't require at least one rod to be replaced. Unless it was a main that spun, which I have also seen, but that one ruined the block, it didn't stall and lock up, it kept running.

Hopefully the damage is fairly benign, and the damage can be repaired cheaply.

[HWYSTR455]

My imagination or the one piston pic in post 75 looks like a valve contacted the eyebrow?


.

[chiphead]

He did say this was the first real run. So if the thrust main got hot and turned enough to close off the oil hole, that would cut off oil supply to the thrust main and related rods. Everything starts to seize up from lack of lube. Then he gets off the interstate just before it starts making noise, pushes in the clutch and the engine stops instantly. Best outcome in that situation, really.

What were bottom end clearances? Hopefully .0025-.0032" on mains and .002-.0025" on rods. Those aftermarket rods should have had .022-.030 side clearance. Crank endplay .005-.008" is where I'd want it all.

[77 TRASHCAN]

Originally Posted by HWYSTR455

My imagination or the one piston pic in post 75 looks like a valve contacted the eyebrow?


.

I saw that too, wondering if the valve reliefs were correct for the heads?

[NeighborsComplaint]

Originally Posted by HWYSTR455

My imagination or the one piston pic in post 75 looks like a valve contacted the eyebrow?


.

I saw that too? The Impression of the valve head slightly off-register with the valve relief.

These are not domed pistons, they are dished. If the piston were to come into contact with cylinder head, the perimeter of the piston would smack quench area (flats) surrounding the chamber with plenty of clearance for the plug electrode. Also, if the pistons hit the three plugs and closed their gaps, where are the witness marks in the tops of the corresponding pistons.

The phraseology of spun bearing is just that. The bearing turned (spun) in its journal and the tang on the back of the bearing causes the bearing clearance to close up and wedge the bearing tight against the crank. The bearing and crank heat up wedging eve more tightly and in conjunction with oil supply due to the bearing advancing and restriction or even fully covering the oil hole, the engine seizes. The the inertia of the camshaft turning (slack and free play in the rollers) while the crank stops abruptly sheered the corner of the keyway off.

Also, there is a lot more metal in the oil pan than a chip from the corner of the keyway would create, plus it would still be pretty much intact as the the motor was stopped dead in its tracks when it would have dropped.

[chiphead]

He needs to check for rod small end to piston boss contact. On the motor I just built, I had to have the small end narrowed about .045" to have enough clearance when the crank and rod endplay stacks to one side. That may not lock it up, but it would make metal.

The ferrous metal may be bearing base metal or it may have come from the journals themselves. Could be from rod side clearance if it was much too tight. Can't really tell until you pull it all apart and inspect.

When this thing goes back together, I would check the main saddle clearances and everything soup to nuts.