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  1. #1

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    92 SL 650 Center Piston Damage

    Took the 92 SL 650 out to the lake this last weekend after an engine rebuild and ran it about total of 4 hours. Checked the plugs after each run for the break-in process and they seemed to look good. Brought the ski back home and took the heads off to look at piston wash for better detail of the engine set-up and found that the center piston did not look good. The cylinder head was very pitted and the top of the piston looked to have the same thing and slight damage to it.

    After reading some more post on this website, I'm wondering if this center cylinder has signs of detonation? Or could this be a lean condition? From the looks of the mag and pto I would assume it is running rich from the piston wash but the center definitely looks like something bad has or is happening. I've attached some pictures of the piston's and also the center cylinder head. Below is the list of what was done on the rebuild.

    1. New pistons and rings
    2. New end seals
    3. Blocked off oil pump and running premixed (32:1) for break-in
    4. Upgraded to 3 outlet fuel pump
    5. All new fuel lines
    6. Took apart all of the cooling lines and cleand out.
    7. Checked carbs diaphrams and filters looked to be good.
    8. Did a crank index check before tear down and it looked good.

    I'm lost to what is happening to the middle cylinder and what could be causing it. Any suggestions on what is going on here? Thanks!!!
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  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Were all pieces of old metal removed?

    Were the heads damaged previously and re-used?

  3. #3

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    Quote Originally Posted by xlint89 View Post
    Were all pieces of old metal removed?

    Were the heads damaged previously and re-used?
    Yes, the engine was completely dismantled and all of the old metal removed.

    The heads were re-used but were all in good condition when put back on, smooth with no pitting.

    Are you thinking this look more like some metal got in the top then detonation?

  4. #4

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    Well, after doing some more investigation on this issue and a compression test, the center cylinder was 60 psi compared to the mag and pto at 115, I took the center cylinder apart and found major damage to the piston, rings and cylinder walls. After more investigation it looks like the c-clip on the wrist pin had broken in half and must got caught in the piston and did the damage. So it looks like a new piston, rings, cylinder and head.

    I'm not sure how the c-clip broke but hopefully it is just a fluke and won't happen to the other cylinders.
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  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    OUCH!!!! C clips are supposed to go a certain direction. Also if they are re-used, they can come out. Much like yours.

    C clips are a 1 time use. NEVER be THAT cheap to try and re-use them.

  6. #6

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    Quote Originally Posted by xlint89 View Post
    OUCH!!!! C clips are supposed to go a certain direction. Also if they are re-used, they can come out. Much like yours.

    C clips are a 1 time use. NEVER be THAT cheap to try and re-use them.
    Yep, thanks to this forum and all of the posts I knew not to reuse them and also to make sure that the opening of the clip was facing upwards. So they were all new and placed in correctly so not sure what happened. They were WSM pistons but not sure if the c-clips are all the same or if some brands are better than others.

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    You have to make sure the clips are seated in the groove.

  8. #8

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    Quote Originally Posted by xlint89 View Post
    You have to make sure the clips are seated in the groove.
    To my knowlege they were all fully seated in the grove when they were installed. What was wierd is that only 1/4 of the clip was gone, the rest of it was still seated into the grove and it took some time to get it out to remove the wrist pin.

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    That would be weird.

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