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  1. #1
    Buaidh No Bas howestek's Avatar
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    Angry 3rd Cylinder/Piston is Toast

    OK. I lost 60 psi compression and 200 rpm's at mudbug. Engine quit momentarily then started. Took it to the trailer. Watched everyone else have a ball.
    Anyway, after pulling the head, I could feel a wear pattern in the cylinder @ 100 degrees ccw from the exhaust port. Piston top and cylinder wall reletively dry.
    After pulling the jug, there is metal embedded in the piston on the exhaust port side (see picture) and scratching of the piston wall. The upper edge of the exhaust port is worn and smooth. The powervalve does not extrude into the cylinder, and is slightly withdrawn into the port. There was oil on the cylider wall underneath the rings. Rings are shot. Crank moves easily by hand.
    Any ideas what caused this?? Lubrication failure? Lean condition? Any help appreciated!
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  2. #2
    r33pwrd's Avatar
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    My ultra did the same thing 3 times ended up being a bad line from the oil injection, never saw any damage but under pressure it was leaking out into the bottom of the hull and I never saw much residue of oil. Not sure if thats your problem but I would look at em. Im sure someone else has a better idea of your problem, good luck!

  3. #3
    Moderator Insanediego Joe's Avatar
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    Why does the top of the piston look washed? Did you wipe it off? If you didnt I would say you ingested water. Dont want to comment further until I know if you wiped the dome off with a rag?

  4. #4
    Buaidh No Bas howestek's Avatar
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    The piston top is not as "pristine" as the picture makes it out to be. I did wipe it slightly, but it is the same color as the other piston tops (black with some carbon buildup). I've taken about 10 pictures of the piston top and they all come out looking silver

  5. #5
    Moderator Insanediego Joe's Avatar
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    Its hard to say once you wipe the dome down. I think you had some detonation going on also judging from the picture. Was the head gasket reused or was it a pristine new one?

  6. #6
    Buaidh No Bas howestek's Avatar
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    Quote Originally Posted by Insanediego-RXP
    Its hard to say once you wipe the dome down. I think you had some detonation going on also judging from the picture. Was the head gasket reused or was it a pristine new one?
    The head gasket was a brand new one. I sprayed copper seal on it at the Mudbug after I lost compression, in a desperate attempt to find something "simple". It obviously made no difference. What makes you think possible detonation?

  7. #7
    Moderator Insanediego Joe's Avatar
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    Hard to tell from the pics but... I think I see small pitting on the dome which is a sign of deto. Can you see pits on the dome or is it just the pic?

    How long after spraying copper coat did you ride the ski. Typically copper coat needs to set for 24 hours before even cranking the engine.

  8. #8
    Buaidh No Bas howestek's Avatar
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    I didn't ride it after the copper coat. It didn't help compression so I called it a day. Later, I found the wear pattern on the cylinder wall. I'm glad I didn't continue riding it. Note: A local mechanic also suggested deto after looking at it although I cant see any measurable pitting. There was some material around the perimeter of the dome that looked like pitting, but I believed that to be metallic material from the piston, or the cylinder, deposited on the top outermost edge of the piston. If I can find a magnifying glass, I will verify.

  9. #9
    Moderator Insanediego Joe's Avatar
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    can you take a picture of the other pistons please. thanks.

  10. #10
    Buaidh No Bas howestek's Avatar
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    Here's the best I can get. #3 does look a hair lighter than the others. All have some carbon on them.
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