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  1. #1

    785 - can I replace just one out of the 3 pistons with a 750?

    A while ago I purchased a 97 pro 785. It has a few nice parts including a 93 octane head. The MAG cylinder let go after MUCH abuse. I am looking to rebuild that one cylinder with a 750 piston like most people do, however, I cannot find in a search if anyone has ever just replaced one piston with the 750? It seems like most do all 3. I'm thinking there might be a weight difference between them, which is why all 3 are necessary.

    What is my best bet for repairing the cylinder itself? Should I get it sleeved? The gouges are pretty deep, I'm not sure a bore would take it far enough to get past them. Plus, I'd probably have to go so far over that I'd have to do the other 2 cylinders to match.

    When the cylinder went, it took the (I think it was Ocean Pro) head with it, the top of the mag portion is pretty banged up. I'm assuming my best bet for replacement there would be a stocker as I don't want to pay for an aftermarket replacement.

  2. #2

    Join Date
    Sep 2006
    Kanchanaburi Thailand for the next 2 years
    The cylinder is Nikisal plated any cannot be sleeved. You would have to send it out to be replated, US chrome had a 785 cylinder on eBay for 259.00 Your other option is buying a used 785 cylinder. Is the damage into the plating itself ? First try some mutric acid, and see if the bore cleans up. I did at one time just replace one piston with a wsm 750 piston to get ready for a race, worked, but to do it right, would replace all pistons with same weight piston. On the head, the dome should be replaceable, Bob, (lugs 785), Art, Kevin, etc, should have a dome for you. I'm sure the same guys will chime in as well, as they know 785's.

  3. #3

    Join Date
    Aug 2006
    Homer Glen Il.
    You can sleeve them but to me it's a waste of money and I would renicasil the cylinder and no I would not advise running a 750 piston with two,stock pistons the 750 piston is much lighter .I have good used cylinders and new and used factory pistons to sell also and I have new domes for your head also pm if interested

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