Hello,

I recently dropped my 350 block off at a local machine shop to have the usual work done to it. Something that needed to be done was to have the small scratches removed from the crank journals. The shop determined polishing would do and the journals didn't need to be turned down. Sounded good to me as the bearings pulled from the block were in great shape.

Got the block and crank back, noticed there were still a couple scratches on a couple of the journals I can feel with my fingernail. Contacted the shop and they said polishing will not remove all of the scratches, but will knock down the edges of the scratch that could damage the bearing. This is a very reputable machine shop in my area. Kinda the go to place for everything from mild builds like mine to the big dollar drag motors. So I tend to want to believe what they are saying.

Are these small scratches ok or should I have expected a perfect surface on the journal? I can provide pictures if they will help.

Thanks guys!

 

Yes, pics needed.
You certainly won't get a better answer here with people guessing blindly, compared to the advice of the machine shop with the goods right before their eyes!

 

That would be my answer also.

When polishing the crank, they're only taking the high spots off. It it's sanded down too much the it becomes a thousand of an inch undersized it will increase the space between the crank and the bearings allowing lower oil pressure.

If we're talking normal bearing clearances of 0.003-0.005, removing 0.0005 of an inch off the surface will increase bearing clearance 0.001

If your old bearings had no damage then polishing the crank and still feeling small scratches with your fingernail isn't going to hurt the new bearings.

 

Here's some pictures. Like I said the scratches are very small but i want to make sure its right before I put the engine back together.

 

That doesn't look "polished" to me. What did they charge you for that "polish"?? You really may need a regrind.

BTW you can hand polish a crank w/400 grit and a leather strap - Chevy Power Catalog shows you how. And you can buy brgs +0.001" oversize.

How do much do want to spend on that crank? Good quality cranks are like less than $300.

 

look at my user name. i'm just a dumb shadetree wrench. First, i wouldnt pay any bill or take any more work to that machine shop. IMO, that crank needs turned. no way i'd go through building an engine with that. would you sleep good at night?

 

So the vote is to take it back to the shop? As i said this is a reputable shop. They did and excellent job on the block. Called them and said they will look at the crank and correct it if there are any issues.

 

I would take it back, this is a pic of the crank in the used motor I bought off craigslist...