Wasted main

[larrym]

So a buddy of mine had used motor he was installing in a roller he had. It was running when he pulled from the other car.
 He was just going to change the rear main on the stand and the bearings looked a little suspect we both felt it looked like contamination.
He pulled the crank and took it in for a polish apparently 1 rod journal was out of round. When we pulled it apart we saw no evidence on any rod bearings but the machinist is very anal so he had the rods turned .010 and the mains polished.
Put it together it lasted 3 weeks clearances were all around .020 when assembled and now one of the caps is loose in the register main bearing on the cap side is toast. It fit tight when assembled and needed a persuasion to come apart.
Rods seem fine so starvation seems unlikely   
Bent crank?
Cracked block?
Cracked crank?

[Scoobum]

3.8? Steel or stock caps?

[larrym]

3.8 stock caps and fasteners

[Steve Wood]

sounds like the bolts lost tension and the cap walked

[larrym]

They appeared to be torqued when disassembled I'm going to stop by and have a peek tonight. 

[TexasT]

Did he use a torque wrench to break em loose? That would tell a story if it didn't take much to break it loose.

Might torque the caps back on ans hit em with a  spring gauge across several different angles to see if any out of round.

[larrym]

I just left his place the 2 centre bears are cooked got very hot.
He said the fasteners were tight coming off. If there was an oiling issue would it not show on the rods also?

[Scoobum]

I'm very specific when I have my engines built. A machinist should check the mains with an elongated dial indicator. Each main is checked at 12, 3. 6 and 9 o'clock. If plastigauge showed evenly across the face of each main for clearance...an d the crank turned freely...then I'm at a loss to explain what happened. The main "tightened" up for some reason. The block, cap and crank will have to be magged for heat cracks.

[Steve Wood]

No oil,  or too tight of clearance

[Scoobum]

Larry...ask your friend if those 2 caps have the chamfer in them that fit into the block. I've seen this before.

[larrym]

 I inspected number 3 cap pretty closely it looked ok I did not see any thing that looked chipped cracked or abraded where it fits into register. It was very loose number 2 was tight.

[Scoobum]

Larry, I saved the 4 main caps from the block I had to scrap last June due to the cracked cylinder. If we haven't sold them...do you want the two center caps? If they aren't sold...you can have 'em.

[larrym]

Thanks Brad if the block checks out he will probably go with billet caps either way  he would need to have the cap fitted to the block and a line bore. Should know more by the weekend as to what direction he is going to go.
I just want to figure out what happened the block could be a boat anchor.   

[Scoobum]

Be sure to inspect the new caps for the chamfer to match the block. Bought an engine from one of the locals a few years back. He kept taking the mains out of it on startup...3 times. He reluctantly sold me the engine. Had a look at it...and the two steel center main caps didn't have the chamfer on 'em. His machinist torqued the caps down each time...and align honed it...degreased it...and handed him the block each time. If his machinist had of loosened the caps and then retorqued them and rechecked...li ke your suppose to after and align hone/bore...he would have noted they were tight/loose all over the place like I did when I checked them. I took the caps/block to a friends machine shop and had the caps machined to fit the block...and had an align hone done. Engine is still in service to this day.

[larrym]

So would a couple backfires from a bad coil pack be enough to bend a crank?
He is going to check the crank tonight, if it was bent that would explain the hammered cap pulling the edges out of the register or would the heat be enough to distort the cap, its not blued.