Spun Bearing?

[AMXguy]

I just bought an untouched running '71 440 for my new project, but when I pulled it apart it has a spun main bearing on #4, it doesn't look too bad and the bearing doesn't show that much wear but it was defietly spinning . what's the deal with this? is it worth going any farther or should I just find another block since they aren't a high dollar deal? I've never had to deal with this before.

[Topcat]

Whats the journal look like? any pics?

[AMXguy]

Crank looks fine, it's the block anf cap I am worried about, I can't ever seem to get pictures to work on here.

[Topcat]

Send it to me. My e-mail is in my profile.

[Chryco Psycho]

usually the block can be align honed with no problems unless the main is deeply scored & chewed up

[AMXguy]

It doesn't look bad at all, I'm not argueing the line boreing can fix it but how can that be? do they use a bearings with a larger OD?

[71chally416]

It ends up being the same dimensions. They just cut some off the bottom of the caps and re-machine the ID.

[AMXguy]

That makes sense, thanks.

[71chally416]

I would avoid line boring if at all possible. It will raise the crank in relation to the cam and you might need a special shorter timing chain.

Bearings spin when they lose their "crush". If the other bearings just fall out when you take the block apart that's an indication the motor suffered detonation. They should require some effort to remove them from the block and the rods. They shouldn't curl up or just fall out, or stick to the crank journals. If it was caught early you might be able to avoid machining. Get a good machinist to look at it and measure the ID. If it checks out OK and the bearing tab locaters in the block and cap haven't been damaged just make sure the new bearing fits snugly in the block and cap and plastigage the bearing when you assemble the motor to double check the clearance 

[moper]

What makes you think it spun? just curious... Is it welded to the crank? are the tangs sheared off? Wish we had a picture. I align hone every engine I do, no issues with timing being erratic. The overall dimensional change between the crank centerline and cam centerline is less than .001" when it's done right. If indeed the bearing spun, get it align bored/honed.

[AMXguy]

I'm computer challenged and my wife is out of town this week or I'd put a picture up, but it wouldn't show much. the bearing had sheared the tabs and was spinning loose , but the crank and the block show very little wear. I took another bearing and put it in there and it held tight on it's own. like has been said it will need line bored but that would have probably been something the shop would do anyway, there is no discoloration or galling so I'm guessing it's going to be fine

[Chryco Psycho]

sounds like it , I guess it was shut down immediatly as soon as the oil pressure changed

[71chally416]

That's the key. Killing the motor immediately when it loses oil pressure or starts to make noise.

I had a neighbor that had a 63 Max Wedge car with the 426. He came over one night and had a rod bearing in his hand that had spun on the crank. It was paper thin and welded together. He insisted that I come to his garage and look at the crank and rod. I crawled under the car with the drop light and I'll be damned if I could see even a slight scratch on the crankpin or rod. I mic'd the crank and it was right on the money. He changed all the bearings under the car and ran the car for two years after that. It gave me newfound respect for the metal they used in those old cranks. The key was he cut it off the second it happened. The oil from the crank pin spraying on the failed bearing probably saved the crank and rod.     

[Topcat]

In case anyone hasn't seen one of these, they're cheap insurance when you get low oil psi. It kills the ignition once oil psi gets to a dangerous level.

http://static.summitracing.com/global/images/instructions/sum-g1438.pdf

Crank looks fine,

Sounds like you really lucked out.

[Aussie Challenger]

usually the block can be align honed with no problems unless the main is deeply scored & chewed up

  When the crank web is perfectly in line then the crank spins more freely, as mentioned before the movement up towards the cam is usually around .001 -.002" which is nothing if you are using a good chain and it is set up properly.       
  If the bearing doesn't make good back contact it will over heat.   
  Remember that the crank has to transmit the power/enery from the pistons back out to the drive train.