Spun Main Bearing Advice

[scca28]

Hi all, haven't been on in a while. My last big project was a rebuilt 4.0 for my '88 Laredo, and one or two of you were working on the same thing at the same time. Got to share in some good advice back then. Now it's been almost a year, the rebuild is humming along just fine. Thought I'd finally get around to tearing down the old motor to see what the noise was all about. Pulled the timing cover and the chain seemed kind of slackish. Too easy. Pulled the pistons, just the usual wear. Undid the front main cap, and there's the seam of the two bearing halves pointing down! Got it all apart, and while the rest of the mains looked okay for 119k, the front bearing had really scored up the cap and the block, and of course the crank. Well defined hills and valleys, like running your thumbnail over the face of a shiney new quarter. Yeh, that bad...
My question at this time, do I throw the block in the dumpster, or is there a resonably priced procedure to repair this at a shop? The reason I say "resonably priced" is because engines are still pretty cheap at the u-pull-it, and I'd hate to spend a lot on a major surgery just to make this one useable again. It's really a shame this thing got beat up like this, because the rest of the block, cylinders, etc look great. I had visions of cleaning it up and offering it for sale, or keeping it for another project. Too late to bring it back for a core charge at the yard (besides, he knocked off half the core anyway).
Thanks for any advice you have!

 

[scca28]

Just that quick I found the repair procedure online for anyone who wants to check it out:
http://chevyhighperformance.automotive.com/10317/0708ch-block-repair-basics/index.html
While it's amazing how they can restore what would normally be junk to most people, it also looks very time consuming, and time equals money $$$. Oh well, guess I should start looking to buy a boat to go with this anchor I have...

 

[Durango-Bob]

An engine machine shop can align bore the case and then you only need oversize bearings to make it all work. This is cheaper than an new block.

 

[igotanxj]

Yeah, they should be doing that to all engines anyway. They may have to do it a little longer, but I don't think it would call for a new engine.

 

[92DripCherokee]

Youd have to gauge how deep the scoring is to determine if your old block is salveagable, and if there are over size bearings in that range.

the engine in this chevy article had shallow damage to a main bearing saddle, within tolerances to machine and hone out. After the machining, the crank was going to be something lke .005 closer to the cam, a bit loose but within limits.

 

[scca28]

After the machining, the crank was going to be something lke .005 closer to the cam, a bit loose but within limits.

That was the interesting part. I never would have thought they could mill down the saddles and actually reposition the centerline of the crank. I guess by doing that, you really don't need that much bigger of an oversize bearing, compared to just cleaning up the holes in their original location? Pretty cool.

 

[5-90]

That was the interesting part. I never would have thought they could mill down the saddles and actually reposition the centerline of the crank. I guess by doing that, you really don't need that much bigger of an oversize bearing, compared to just cleaning up the holes in their original location? Pretty cool.

Especially considering the typical "oversize" bearing isn't mean so much as to clean up where the bores had to be opened up, but to take up the space left when the crank has to be reground. An "oversize" bearing complements an "undersize" crank.

Fortunately, the caps can be sanded down slightly at the mating points, and then the whole bore redone by any competent machine shop. It's similar to what would be done if a block is to be "blueprinted" or if a main cap has to be replaced - since main caps are matched to the saddle they're initially machined to anyhow (and any time one is swapped on purpose, it has to be rebored/reground to fit.)

But usually, the "oversize" on a bearing shell is on the inside, not the outside. Small but important difference.