Chevy 350 fresh rebuild crank won't rotate

Discussion in 'GM Powertrain' started by Crawdaddy, Jan 21, 2013.

  1. Crawdaddy

    Crawdaddy has no brakes Staff Member 5+ Years 1000 Posts Platinum Contributor

    My cousin is working on rebuilding his Chevy 350 small block. His original motor was completely trashed, and he got this one out of a junkyard and had a machine shop clean and hone the block. Among other parts, it has a new crank. We're in the process of putting it together and we have 2 sets of main bearings: a standard set and a set of .010 over. Drop the standard set in, and the crank rotates freely, but according to the plastigauge has far too much clearance. We dropped the .010 set in, and the clearance shows right, but even with one bearing run down hand tight locks the crank up to where you can't turn it by hand. I've never seen this before and was wondering what ya'll thought.
  2. Pikey

    Pikey Moderator Staff Member 3 Years ROTM Winner 5000 Posts

    I have seen something like this happen one time. It was when I was in school and we were rebuilding a 350. With he standard size bearings the crank would rotate. When we went to the oversized it would not. I noticed with the stock sized bearings that the rotation felt weird, like it was catching. We pulled the new crank out and put a micrometer on it, we discovered that the crank was not machined properly. It was not round, it was an oval. We measured it one way and then rotated the mic 90 degrees and that is when we noticed the inconsistency. The crank was replaced for free by the company where we purchased it. It turned out that they had hired a new grinder and he did not have the crank setup in the machine perfectly when he ground it. I am not saying that this is your issue, but it may be worth looking into.
  3. Crawdaddy

    Crawdaddy has no brakes Staff Member 5+ Years 1000 Posts Platinum Contributor

    The crank is one that was purchased through AutoZone. It was also supplied with bearings. The crank bearings supplied are the .010 over and the rod bearings are .020 over. That's definitely an idea. A quick googling on my phone seemed to indicate the block may need to be align-honed. I would hope that's not the case.
  4. Crawdaddy

    Crawdaddy has no brakes Staff Member 5+ Years 1000 Posts Platinum Contributor

    Had AutoZone swap the crank for another one, and that one does the same thing. Even tightening down one bearing to nowhere near torque spec is enough to lock the crank solid in the block. We have no clue what the issue is, but it's gotta be in the block. The whole affair's been tabled until he can get the money up to send it off to a shop to have them figure out what's wrong.
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Your thoughts on line honing might be right, doesnt have to be out of alignment by much to stop the crank from rotating.

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