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  1. #1
    PWCToday Regular
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    95 SL750 - my piston is toast - 3rd time

    I have a 95 SL750. Had it for about 5 years. I haven't run it this year yet as I've been to busy. Late in the season last year I put in a new cylinder and piston/rings (on the rear-most cylinder) - after that install I tested compression which was good but I know my carb tuning needed adjustment cause the engine would not run on that cylinder on its own (the other 2 would run the engine independantly).

    Anyway, I didn't run it much last year due to the carb needing tuning so I winterized it. I only today 'unwinterized' it. It eventually started and I let it run for 5 minutes but it did sound rough. Thought I'd test compression before starting on the carb setting and to my surprise the rear-most cylinder again had no compression. I took out the cylinder and piston and sure enough the piston is toast (cyllinder and top though look fine). The piston has a groove/channel on one edge going all the way from top of piston to the bottom - the channel is about 2mm wide and 2mm deep - this channel burnt all the way down including through the rings.

    So I have some questions:

    1) based on the damage I described in the piston, what would cause that type of damage?

    2) I barely ran the motor more than 30 minute since putting in that piston last year - is this enough to damage the piston even if running rich or lean?

    3) I did some reading and I think I need a 69.75mm piston - is this correct? Does anyone know the make/models ofdifferent pistons that would fit. I live in Calgary and parts stores are limited - the more options of different makes/models would help to track one down being that I will otherwise need to buy off ebay but that could take 30 days to arrive.

    Thanks
    Last edited by DanDaMan; 07-23-2017 at 08:43 PM.

  2. #2
    Top Dog Benflynn's Avatar
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    Re: 95 SL750 - my piston is toast - 3rd time

    Pics

  3. #3
    PWCToday Regular
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    Re: 95 SL750 - my piston is toast - 3rd time

    OK, here is a pic - the damage was on the right side of the jetski - the arrow on top of the piston was pointing to the front.

    413478101.jpg

  4. #4
    Top Dog Benflynn's Avatar
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    Re: 95 SL750 - my piston is toast - 3rd time

    Something got in there, I'd look to see of the reeds and screws are all there, maybe a crank bearing roller, something from somewhere is in that cyl, and prob pieces of it are still down in the crank case

  5. #5
    Top Dog Benflynn's Avatar
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    Re: 95 SL750 - my piston is toast - 3rd time

    The wrist pin looks like hell too

  6. #6
    PWCToday.com Is My Home Away From Home Chester's Avatar
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    Re: 95 SL750 - my piston is toast - 3rd time

    Why would you re-use that wrist pin? Did you do the bottom end too?

    Chester
    Speed is very expensive. How fast do you want to spend?

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  7. #7
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    Re: 95 SL750 - my piston is toast - 3rd time

    to answer some questions, and some of my own

    - no I didn't do bottom end at all - simply bought a used cylinder, piston, rings from ebay and installed - did that twice already over the last 5 years.
    - what is wrong with the wrist pin - it has no grooves or etches - smooth as a babys bottom
    - I turned over the engine just now (with the cylinder and piston off, and a string on the rod to keep it up and in the centre) - there was no sign of anything in the bottom end. I also removed the rod/piston bearing (with rollers) and there were none missing. Not sure what got in there but I think it must have gone out the exhaust??
    - gonna call some shops tomorrow to try and find a new piston and rings - do I just state I want 69.75mm piston, or are there other measurements I need to provide them. Any specific make/model of pistons that will work.

    Thanks

  8. #8
    PWCToday.com Is My Home Away From Home Chester's Avatar
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    Re: 95 SL750 - my piston is toast - 3rd time

    Quote Originally Posted by DanDaMan View Post
    to answer some questions, and some of my own

    - no I didn't do bottom end at all - simply bought a used cylinder, piston, rings from ebay and installed - did that twice already over the last 5 years.
    - what is wrong with the wrist pin - it has no grooves or etches - smooth as a babys bottom
    - I turned over the engine just now (with the cylinder and piston off, and a string on the rod to keep it up and in the centre) - there was no sign of anything in the bottom end. I also removed the rod/piston bearing (with rollers) and there were none missing. Not sure what got in there but I think it must have gone out the exhaust??
    - gonna call some shops tomorrow to try and find a new piston and rings - do I just state I want 69.75mm piston, or are there other measurements I need to provide them. Any specific make/model of pistons that will work.

    Thanks
    That pin in your hand is trash. Find out why it failed before you put anything back together.
    You have to completely take apart the engine to carefully inspect each bearing and replace the seals. What was the cause of the original failure?

    "...no I didn't do bottom end at all - simply bought a used cylinder, piston, rings from ebay and installed - did that twice already over the last 5 years..."

    If you can't afford to do it right, how can you afford to do it over and over and over and over...

    Chester
    Speed is very expensive. How fast do you want to spend?

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  9. #9
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 95 SL750 - my piston is toast - 3rd time

    You can see the marks on the wrist pin made by the rollers of the wrist pin bearing. The reason you can see then is because rust has pitted the pin surface. Run some 320 wet sandpaper over that wrist pin then hold it to the light at an angle and youll see all the pitting on it. That pitting causes vibration and premature failure of the wrist pin bearing.
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  10. #10
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 95 SL750 - my piston is toast - 3rd time

    What else was did you reuse despite the rust damage?

    Did you install the piston with the arrow pointing backwards?

    Have you installed a primer in the last couple years. A choke screw could have
    been sitting inside the reeds.


    Bill M.rust damaged rings.jpg
    Last edited by wmazz; 07-24-2017 at 02:17 AM.
    Horsepower == Speed, RPM != Speed



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