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Thread: Piston analysis

  1. #1
    bowsniper's Avatar
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    Piston analysis

    I found out when my Slt stopped on the lake, the reason why is because the impellor got jammed in the pump. I took the motor apart and this is what i saw. it was still running in this condition too. Ran great actually.48-49 mph! What was wrong in each cylinder besides the destruction seen?. Lean obviously,,,any of these look indicative of a certain thing going on? I'm just trying to learn from this example.
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  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    At least one of those pistons looks like it has debris damage around the top perimeter.

    What is the cylinder sequence, left to right?

    Are all the photos in the same order?

    Were any of the pistons dropped or dinged after they came out of the engine?
    Looks like nicks in one or two of the piston top edges.

    What do the cylinder walls look like?

  3. #3
    Moderator beerdart's Avatar
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    From left to right. Lean, Lean, Lean + broken ring.

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    bowsniper's Avatar
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    Question 1 yes,2 yes, 3 no, 4 no idea- I'll take a couple pics right now to show. So if they are lean, that might suggest the last owner of the ski whom.....Installed copper gaskets and a ocean pro head and ocean pro F/A's. on it.
    Does it look like he didnt adjust the carbs correctly for the new setup? Could of this been the reason why it's falling apart from misadjustment?
    What adjustments would of have to be done to correct this situation? High screws. lows? how far out more?










    left to right 1,2,3, all pics except individual close ups. just use the piston pin to follow which is which. i never take it out--- unless shes 5-6 120 lbs, 34-c or bigger/\/\ opps!
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  5. #5
    thester71's Avatar
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    hey, what is that next to your coffee cup on that paper?

  6. #6
    mr. happyfunbear tenjuna's Avatar
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    regarding what to turn and how much...you might benefit from starting the tuning cycle over from scratch.

    here is a short summary from memory learned from randy @ watcon, obviously you might have to wait to do this when it's warm out...also, if I am incorrect in any of the steps my apologies, someone please correct me. this is how I did my own ski, so I am reasonably sure this is correct.

    turn the highs and lows all the way in until lightly seated, counting the turns and writing them down for future reference.

    start by turning out the lows to the factory specs, then do 20-30 yard runs at half throttle. what you are looking for is a nice clean burst out of the hole. if it bogs or gurgles, you are rich, so turn them in 1/8th and try again. if it hesitates or misses it's lean, so turn them out 1/8th and try again. you don't want to go too far or too long, as we don't care about speed, just the initial burst of acceleration.

    the point is the lows determine that first grab when you dig into the throttle, so you tune them first.

    once you are reasonably sure you got it, turn out your highs to factory specs, and do the same 20-30 yard runs at 1/2 to 3/4 throttle. what you are looking for now is a nice transfer of power from idle to 3/4. same thing, if it bogs it's rich so turn them in 1/8th and try again. if it hesitates or missed or stumbles, it's lean so turn them out 1/8th and try again.

    I will keep saying it, DO NOT GO WOT. we don't care about speed yet, we are looking for a nice transfer of the various fuel delivery routes.

    once you have a nice grip of acceleration, and you have resonably minimized gurgling, bogging or stumbling and missing, then we fine tune.

    to do this, you will need a tachometer. you can get a tiny-tac (you want the 2X model if it's 3 cylinder) at ebay for $25.

    open up the highs another 1/8th out and do a WOT run, checking for max RPM on the run. on my ski max RPM is 6300 so I want to be as close to that number as possible. on yours, you will have to look it up.

    then turn the high backs in 1/16th, then do a 2nd run.

    if the 2nd run results in higher max RPMs, turn them in another 1/16th and do another WOT run. if the max RPMs are higher yet, keep repeating until the max RPMs are lower, then go back out 1/16th. congrats, you have fine tuned.

    if your 2nd run instead resulted in lower max RPMs, turn them out 1/16th and do another WOT run. repeat as necessary until max RPMs have peaked and are going lower, then turn back in 1/16th. congrats.

    this took me an entire day to learn and perform at the ride in Utica and I got to ~6080 RPM. your mileage may vary.

    hope that helps.

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    One of those pistons is different from the other 2. Doesn't have the deto rings between the piston rings.

    Wiseco changes the design without notice.

    Was it larger than the other 2?

    The rust color concerns me. Is that from sitting, or was that the way they looked when removed?

    One of the piston's rings wasn't sealing well. You can see all the carbon built up between the rings.

    I'd be curious to know what the clearances were?

    Definately had foreign material floating around one cyl.

    Another piston does have 2 good dings on the edge of the dome.

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by bowsniper View Post
    ...It was still running in this condition too.

    Ran great actually.48-49 mph!...
    With 2-stroke engines, it is often said they run best just before they go boom

  9. #9
    bowsniper's Avatar
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    wow nice analysis of tuning tenjuna! thx, xclint--great insight on this stuff!One of those pistons is different from the other 2. Doesn't have the deto rings between the piston rings.

    Wiseco changes the design without notice. I didnt even see anything

    er 2?

    The rust color concerns me. Is that from sitting, or was that the way they looked when removed? was on the piston, it's more of a tan burn

    ll. You can see all the carbon built up between the rings. ill look closer. what does that mean? bad rings? or weak or not seating?,just old or from destruction?



    .

    Another piston does have 2 good dings on the edge of the dome. may have dropped it. but not like it was in a car trunk.

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Top left pic:

    Notice around the compression rings, the small "Ruffles potato chip ridges" on the left and center? Then the right piston is smooth in that area.

    That was something Wiseco would change during production.

    If that tan burn isn't rust, I'd be thinking those pistons got very hot and was burning the oil that was lubing them. I'm just guessing on that. Randy would be a good person to take a look at these.

    Top left pic again:

    Notice the black carbon build up between the rings? Top ring wasn't sealing for squat!

    Bad rings, weak, or not seating all mean the same.

    Improper break in. Too much ring end gap. Cyls not properly bored or out of round.

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