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change crank in sbc?

Discussion in 'The Hokey Ass Message Board' started by Dan, Feb 13, 2012.

  1. Dan
    Joined: Mar 13, 2001
    Posts: 2,370


    can the crank be changed without pulling the pistons out? thanks-
  2. sheltonk7
    Joined: May 30, 2011
    Posts: 46


  3. sy1356
    Joined: Dec 31, 2005
    Posts: 96


    Yes, Have done it many times
  4. whid
    Joined: Jun 20, 2008
    Posts: 452


    yes X2....whid

  5. sheltonk7
    Joined: May 30, 2011
    Posts: 46


    if you can stand the block bellhousing down on a couple of 2x4s makes it lots easier
  6. Sounds like a pia if your changing out the crank .. fitting main and rod bearings, pulling the clutch, frontend, etc and re-install on your back ..... why go this route? I assume you are talking, still in the car.
  7. Dan
    Joined: Mar 13, 2001
    Posts: 2,370


    not in the car, we plan to pull the engine out...
  8. Good, you had me skeered! LOL
  9. Dan
    Joined: Mar 13, 2001
    Posts: 2,370


    students are making the swap, trying to figure out the best way to get it done, with a dozen different kids having a hand in it, thats whats skeery :)
  10. chaos10meter
    Joined: Feb 21, 2007
    Posts: 2,191

    from PA.

    Not skeery, that's the way to learn.
  11. raengines
    Joined: Nov 6, 2010
    Posts: 227

    from pa.

    how are you going to get everything cleaned????
    this don't sound good
  12. I'm not liking the sound of this either.

    Changing the crank ???
    I'm thinking balancing problems unless the entire rotating mass is removed.

    If it was the original crank going back in then I would be a little more eager to say go ahead. If this is a teaching / learning opportunity then I'm thinking you're teaching bad habits from the start. Pull it all out, inspect, clean, repair as required and re-install.
  13. burnout2614
    Joined: Sep 21, 2009
    Posts: 612


    I have done this MANY times, don't recommend it. Use fuel hose (or some tubing) on the rod bolts to keep from denting the crank journals. Yes, denting, I never just scratched one. peace
  14. dirt slinger
    Joined: Jan 30, 2010
    Posts: 645

    dirt slinger

    I always thought it was necessary to line bore a block if you were changing the crank or at least make sure all clearances were proper. Is that true?
  15. Dan
    Joined: Mar 13, 2001
    Posts: 2,370


    The previous balancer came loose from the crank snout and buggered up the very end of the crank, the key way is damaged but that looks to be it. Is it possible to have the end of the crank welded up and have a new keyway machined in? The only reason I ask is that the rotating assembly is balanced - but if welding and machining on the crank would the "balancing" still be okay or is the whole mess gonna need rebalanced anyhow? This is a 350 block with a supposed 327 crank (we have to measure the journals and check the numbers) the rotating assembly on this setup balanced with the harmonic balancer in place? I agree I would like to tear the whole thing down and do it "right" but this is a kids engine and he has no money to put into it so I am just trying to get him by as cheap as possible - I know this is not the best option but it is the reality of the situation...
    If this is a large journal 327 crank would the 350 rods and pistons have been used? If it is a small journal 327 crank would some sort of spacers have been used in the mains or just special bearings??
    Its kinda an intersting engine, looks like at one time alot of decent, correct work had been done but now its been through a number of owners and alot of things are pretty shady...
  16. willowbilly3
    Joined: Jun 18, 2004
    Posts: 4,356

    Member Emeritus
    from Sturgis

    They are usually balanced with all the rotating mass. But, I would think just building the crank back up and machining in a new keyway wouldn't affect it much since that is so close to the center of the rotating mass and you really shouldn't be adding anything that wasn't there before. It won't be a high revver or a race engine but you are just trying to get some broke kid by and if he doesn't throttle jockey it he might drive it quite a while. I welded a harmonic balancer on for a guy once so he could try to get home across a couple states. He stopped in 2 years later and said he was still driving it every day. Not the kind of stuff we are proud of but sometimes you can get away with stuff like that.

  17. You only align bore or hone a block if it is necessary to make the bearing saddles straight. One makes the assumption that the saddles are alright in an engine that has been running. The crank doesn't have anything to do with bearing saddle alignment.

    To properly build an engine it is certainly desirable to check all clearances and rectify any or all of them out of tolerance prior to final assembly. But that is not to say that an engine cannot be screwed together without doing so. Many engines get packed without taking a single measurement, it is a common thing for a non professional engine builder to do.

    I have changed a crank or two without removing the head. These were normally an emergency situation just to get it running and away from where it was. I recall changing the crank in a Ford Ton van in the middle of tthe jungle in S mexico while I lived there. Some fellas from the states came unprepared and spun several bearings. The mamaged to get a crank sent to them from the states along with a new set of bearings. I layed on my back in the muck and patched it back together for them so they could go back with their tails tucked.

    The engine did fine all the way to Dallas. They called from there and said they made it home safe no rattles in the lower end and holding oil pressure.

    All that said it is a stop gap measure at best.
  18. dabirdguy
    Joined: Jun 23, 2005
    Posts: 2,404

    Member Emeritus

    External damage (outside the oilpan ) is the ONLY reason I might consider pulling just the crank.
    That is, of course, assuming all the debris from the problem fell outside the oil seals.
    Joined: Aug 7, 2009
    Posts: 2,069


    He'll have to buy a couple gaskets anyway, buy a complete gasket set for $10-$20 more & take the pistons out, let them all know, "it ain't no thang". The LEARNING EXPERIANCE is key!!!!

    FYI - I got a machined 60 over 327 unbalanced crank for $75 with bearing from a local rebuilder & used headgaskets, with some engine paint on them for sealing, in my 4spd chevelle about 150,000 miles ago. Still drives Bad Ass!!!
  20. SLAMIT
    Joined: Sep 9, 2002
    Posts: 929


    considering the situation I think what you are doing is fine. cranks are cheap. machine work isnt! id say go ahead use plastigage when screwing it back together to check the clearances. if it checks out button it up and run it. what is the worst thing that could happen? it's a smallblock. they will run! worst case is that the motor doesnt last long. then its craigslist time and find another 350 for a few hundred bucks and do another swap.

    By the way. good job helping the kids out. its why we should all be here to pass on the knowlege. and let them all get in and get greasy. it may take an extra few days if they all get in there but it will be a lifetimes worth of experience for them all and a memory that they wont forget. couple that with the self accomplishment and its a win all around
  21. jesse1980
    Joined: Aug 25, 2010
    Posts: 1,355


    if your going to do all that work you might as well put a new gasket kit and rings and bearings in too. just my opinion is all. you would be half way there and it would suck to have to pull the engine out for something stupid a second time.
  22. GassersGarage
    Joined: Jul 1, 2007
    Posts: 4,728


    I've actually done it on a '68 Corvette. However, I also pulled the pistons to re-ring it too.
  23. yes what he said, that will be the tough part,not nicking the new one

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