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  1. #1
    scottr2200's Avatar
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    lost compression in mag cylinder

    I took out my sl 650 today for its maiden voyage. All seemed well. I was putting around a little. a little wot then she shut off at wot. So I was scared and got pulled back to shore. I trailered it and pulled the plugs all looked well. I did the thumb test ... pto good.....center good..... mag none. turned it over until the mag was top dead center. looks good. no hole. but what happened?? I got home pulled the cooling rail and the head. cylinder looks good. no scratches in the walls. piston looks good. Did i blow the head gasket??? It looks in tact. would it be noticeable if i did?................. darn, I just went to take a photo to post and seen the smallest ding in the top edge of the piston. ran it all the way to bottom and there is some metal on the wall of the cylinder. Im guessing it took out my rings. The pistons I have in this thing are 1.00mm over. Where do I get rings that size? also should I just hone it out and re-ring it or do I need a new cylinder for it? It doesn't look bad at all. ..... man i am bummed. I made sure this thing was well cleaned out too. How did this happen?
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    Last edited by scottr2200; 09-16-2007 at 04:31 PM.


  2. #2
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    I've cleaned up alot of cyls with a hone from Autozone(borrow it),Looks like you need to pull the jug and see what to the piston.Can you get a good picture of the piston top and the damage. I've got pistons quickly from here.
    http://myworld.ebay.com/jkwaterparts

  3. #3
    scottr2200's Avatar
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    I will pull the jug off tomorrow after work and then maybe I can get a better pic. That was the best I could get as it was. I can never get very clear pics on my camera when I try something up close like that.

  4. #4
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    I have a ski that spit out the little roll pin that is used to keep the rings from turning.Check to see if you lost it when you get the jug off.

  5. #5
    scottr2200's Avatar
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    piston is shot

    I pulled the piston and cylinder today and the piston and rings are tore up real bad. The cylinder looks like it will be ok with a little honing. I looks like the roll pin came out that keeps the rings from spinning. It is right between the gap on the top ring where the damage started. Here is a pic. the best i could get.....

    Also does anyone have a piston and rings for a 92 sl650 that is 1.00mm over???
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    Last edited by scottr2200; 09-18-2007 at 07:40 PM.

  6. #6
    Moderator beerdart's Avatar
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    Witch way is the arrow on the piston pointing?? I have a new .5mm over.

  7. #7
    scottr2200's Avatar
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    It points at the exhaust. pin goes from left to right arrow points to the exhaust. This was already 1 mm over. I just purchased one on ebay for 71 dollars. (I am impatient)

  8. #8
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    Lets Address This

    OK GUYS,What causes this?I was told by Detonation possibly.But top looked perfect.Bad quality?What's the thoughts? This was a W7A25 Piston, Polaris I think.

    Here's mine.
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  9. #9
    ph2ocraft's Avatar
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    Quote Originally Posted by scottr2200 View Post
    I pulled the piston and cylinder today and the piston and rings are tore up real bad. The cylinder looks like it will be ok with a little honing. I looks like the roll pin came out that keeps the rings from spinning. It is right between the gap on the top ring where the damage started. Here is a pic. the best i could get.....

    Also does anyone have a piston and rings for a 92 sl650 that is 1.00mm over???
    When you went oversized, did you have the cylinder bored?
    What was your ring gap?
    Were the oil lines bled and free of air?
    Were you able to leave a drop of water on the cylinder without it boiling off?

  10. #10
    ph2ocraft's Avatar
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    Any pictures of the plugs. dome and piston top before you took it apart?

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