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  1. #1

    Join Date
    May 2008
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    Phoenix,AZ
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    Help with diagnosing piston problem- updated pics page 2

    Hi,
    My 97 slt 780 was rebuilt 2 summers ago and since then like clock work I have lost all three pistons. Maybe 10hrs apart or less. First the mag, then the center and now the pto. They all looked like the pictures I am attaching. the engine builder here in Phoenix says that it is detonation/lean condition. He checked the carbs says OK. On this last one I also pulled the fuel pump but before I go back to him I wanted some advice from you all.

    I did search here and that is how I found the pictures, they look exactly like my pistons and head, the thread suggested that it was piston slap or crank bearings causing the pistons to clatter. The thread is fom September 06 and I haven't come across a similar one yet. I am still searching but I thought I would try this way also.

    Thanks,

    Chuck
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by MohaveChuck; 05-13-2008 at 06:47 PM. Reason: Updated Pics


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    What grade of fuel are you using?
    Old gas, or water in the tank?

    Has the compression been increased from stock?

    Were all three pistons that clean on top when you pulled them out? No carbon pattern at all?

  3. #3

    Join Date
    May 2008
    Location
    Phoenix,AZ
    Posts
    8
    I always used the same fuel from the same Chevron station 92 octane. I use it in a 93 Kawasaki 750 standup and in a stock 454 carburated boat engine. Fresh gas and my son was just cruising definately not WOT since we were still breaking in the last piston.

    I don't think they increased the compression. I didn't ask for it and it was never mentioned the other two times I took pistons in to them. I spoke directly with the engine builder.

    The other two pistons are not clean on top, about 90% covered in carbon and maybe a little rougher than they were new. I can take pictures this weekend.

  4. #4
    pm me the builders name

  5. #5
    ps it looks like a slap issue or a contact issue how was the small bearing? and how's the crank?
    is the builder fixing these for free?

  6. #6

    Join Date
    Jul 2007
    Location
    Alabama Gulf Coast
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    206
    I'm not at home so I can't show pics but that piston and head looks an awful lot like mine when I lost the wrist pin bearing. Hmmm?? Are you still running the oil pump or have you converted to premix for assurance of oiling?

  7. #7

    Join Date
    May 2008
    Location
    Phoenix,AZ
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    8
    small bearing looks fine.

    I don't know how to check the crank it looks OK.

    I am still running the oil pump but I had extra oil in the gas because I was still breaking in the center piston that went at the end of last fall. 3 tanks of gas with extra oil right?

  8. #8
    I'd start over! get the crank inspected! go thru the carbs , check the bores for excessive clearance then decide what size piston, do it yourself so you don't count on that shop .It will cost less and run better, longer
    Last edited by ZMANN; 05-07-2008 at 06:34 PM.

  9. #9
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    Get us pictures of your problems,The pictures that "look just like mine" really doesn't help us,because what looks simular to the untrain eye can be totally different to us.

  10. #10
    Moderator beerdart's Avatar
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    Quote Originally Posted by Keddano View Post
    Get us pictures of your problems,The pictures that "look just like mine" really doesn't help us,because what looks simular to the untrain eye can be totally different to us.
    So now you have a trained eye to go with the Horse and Dog.

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