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Technical Sleeve it or bore it...

Discussion in 'Traditional Hot Rods' started by trey32, Aug 5, 2020.

  1. trey32
    Joined: Jul 27, 2014
    Posts: 297


    I got a 59 flathead block I'm getting ready to send off to the machine shop and all the cylinders are at 3.30X".
    My question for everyone is should I be born g this thing to 3 5/16"-3 3/8" or should I sleeve it and get it back to a stock size bore??
    It's getting a Merc crank and 29a rods just not certain the large piston size is the right answer. Would I be able to bore it again??
    Thanks for the help!!
  2. Marty Strode
    Joined: Apr 28, 2011
    Posts: 6,726

    Marty Strode

    I would bore it to 3 -5/16, with the Merc crank it will be 276", good combo.
    belair and Blues4U like this.
  3. swifty
    Joined: Dec 25, 2005
    Posts: 1,917


    But Marty that only gives him 12 1/2 thou to clean and true the bore. Is that possible or do-able? He could go 3 5/16 plus whatever oversize the machine shop needs to give him a good bore.
    olscrounger likes this.
  4. Sonic test & pressure test first. Offset grind the merc crank to 4 1/8 bore what it needs 21A or 91A rods & now you have a great engine.

  5. Marty Strode
    Joined: Apr 28, 2011
    Posts: 6,726

    Marty Strode

    Ross Pistons, made us a couple of sets 3-5/16 plus .030. Any competent machine shop could run a dial bore guage through the bores, and tell if it will clean up at 3 and 5.
  6. Do the smallest over bore that will clean it up.Remember you have 70 years of erosion working from the other side of the cylinder.
    AHotRod, Boneyard51, belair and 3 others like this.
    Joined: Jul 26, 2008
    Posts: 59
    from 14883

    Trey, I have a 8BA punched out to 3 3/8" it has many thousands of miles with no problems. I have noticed it gets 10-15 degrees warmer on long hills but never overheats. If you go that big be sure to check piston to head clearance. The head overhangs the bore and can hit the domed piston. Have fun,Chuck
    kidcampbell71 likes this.
  8. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,986

    jimmy six

    Make sure rings are available before you start anything. Pistons can be made any size; for me it’s the rings.
  9. sunbeam
    Joined: Oct 22, 2010
    Posts: 5,597


    Why worry about a rebore are you going to drive it over 100.000 miles?

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