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  1. #1

    Good Compression, Scored Piston 65u 1200

    So long story short, I just picked up a used 1200 engine that has apparently 50 hours on it since it was gone through. It is in SBT engine. Anyways, I have got even compression across the board, 110, but I when I inspected the pistons through the exhaust ports, I noticed piston #3 was scored. From what I can see through the exhaust port, the cylinder looks and feels good, AND it has good compression. To top it all of, as a preventive maintence, I just replaced the cranks seals and found NO debris what so ever in the crankcase halves, and the cylinder walls looked great from that view.

    I am debating on whether or not I should tear down the top end and replace that piston? Have you guys ever experienced scored piston with perfect compression?

  2. #2
    Quote Originally Posted by FlMike View Post
    You should check with SBT before tearing down to see if its still in warranty. If it is you'll get a new engine for free. If you tear it down first you'll void the warranty.
    Yeah I am going to give them a call today and see what they say. I am not sure exactly how old the motor is. Is the warranty transferable?? I will be curious to hear what they say.

    It's just one of those things I guess. I am having a real hard time dropping this motor in and using it and being confident in its performance! My biggest fear is a chunk of the piston skirt breaking off and losing a bottom end. Kind of a bummer! I bought the the motor with the intention of it being a drop in but it has turned out to be a little more than that! At least I'll know what Im working with!!

  3. #3
    No warranty Just got off the phone with Lynn at SBT. Ran up awhile ago! It was worth a shot!

  4. #4
    Myself's Avatar
    Join Date
    May 2007
    North Central Arkansas
    How bad does the scoring look? Any pics? A scored piston will not affect compression numbers. The piston does not make the seal, the rings do.

  5. #5
    I believe it is perfectly acceptable to have a scored piston reused. in the shop manual you will see the method for cleaning up a piston if you are rebuilding the motor. I would assume that someone rebuilt the top end and maybe bored or honed the cylinders but reused the piston or bought a used piston and cleaned it up a little. I wouldn't touch a thing if the cylinder walls look good.

  6. #6
    Thank you guys for the advice!! I will snap a photo and post it so you can see what I'm talking about. I know the 65u is a GOOD strong motor and I want to make sure it lasts. Compression is even and the cylinder walls look good. I am thinking along the same lines as you guys.Previous owner rebuilt the motor, freshened it up with rings and used the scored piston. I am going to leave it as is and go ahead and install!! Oil injection block off kit and GENUINE OEM Mikuni carb kits are on the way!

  7. #7
    Here's a few pics...compression is good and cylinder feels smooth. I'll let you guys look and see what you think..

  8. #8
    boudin's Avatar
    Join Date
    Oct 2009
    Houston, TX
    If it has good compression, rebuild the carbs, check the reeds, and run it till it drops!
    Last edited by boudin; 03-18-2015 at 05:48 PM.

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  10. #9
    Myself's Avatar
    Join Date
    May 2007
    North Central Arkansas
    Ya, just run it. I've run worse than that before with no issues.

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  12. #10
    Thanks guys!!!

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