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  • #1

    Hole in piston

    I read in the posts in the Tigershark section about a hole in the piston and what happens to the aluminum that used to be in the piston body. Well, I was riding yesterday, and started running really bad (sort of like running on only 2/3 of the cylinders?? ), I pulled the plugs and found one oddball looking one. A compression test, and later a pull of the rearmost head confirmed a hole in the piston [img]graemlins/crying.gif[/img]

    I realize from the postings that the material is in the crank bearings, and a full replacement would be the proper things to do, but I think I'm going to do a top end and see how long it will go before more problems occur.

    Questions: If I have very little scoring, can I get away with just a honing of the cylinder as is and a replacement with a OEM-size piston? If I have to go .5mm over, can this be done to just one cylinder? Who's got the best deal on a one-cylinder kit?

    I'm bumming. [img]graemlins/crying.gif[/img]
    Tags: None
  • #2
    Some people have gone with odd sized pistons, but I don't recommend you try especially on a Polaris crank, it will twist sooner or later because of it.

    As long as your clearance is still within spec, yes you could hone and reuse std. size. You will have to hone and measure first.
    SBT Tech Support is here to help with your problems.
    We try to answer each question quickly and accurately.
    Please do not use Private Messaging for Tech Support, use the forums.

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    • #3
      Hey thanks - at least there is hope I'll get over this hurdle w/o spending major bucks - at least in the short run.

      Other than what I think is my tuning being too lean, what else could have caused this burnout? Top of the piston, just under the spark plug, has a nickel to quarter size dish, with a little smaller than a pea size hole in the middle.

      Also, can one re-use head gaskets? Was put on new late last year w/a case-seal job.

      [ April 28, 2003, 09:08 AM: Message edited by: ShowMeSLT750 ]

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      • #4
        Timing, out of index crank, too hot plug or lean could burn a hole. I wouldn't reuse a head gasket.

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        • #5
          You can easily check the crank indexing by placing the front piston to TDC and making sure the other two are even.
          SBT Tech Support is here to help with your problems.
          We try to answer each question quickly and accurately.
          Please do not use Private Messaging for Tech Support, use the forums.

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          • #6
            Its a 750 blue fuji (actual 744), and its not an SBT motor, I think its the original powerplant - I'm the 3rd owner.

            When you put #1 at TDC, and I'm guessing the mag is #1, how much can the other two be off from eachother? My "problem" is in the rearmost (PTO) cylinder. I got the cylinder off, the piston removed, and while I was looking at it I put it (PTO) at the highest it could go, it seemed like the other 2 cylinders are different from eachother by maybe a quarter inch or so. I did this by a very crude method however (stuck a dowel in and measured the depth) so I may be wrong.

            I plan on getting this one running again at least, and goin from there. I looked at a 2000 Pro 1200 in town yesterday, what a sweet machine. I shouldn't have even looked at it cause I wouldn't be able to afford it w/o major cutbacks on other luxuries.

            Heard the SBT technical support say they don't recommend WSM pistons. Should I go with the polaris, or does anyone else make quality standard size pistons for a decent price? Taking the cylonder in today to see if I can get by with just a honing.

            Thanks for the feedback. Can't say enough for the site, SBT.

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            • #7
              A 1/4" means the crank has twisted quite a bit, it's shot. You need more than just a top-end I'm afraid.

              OEM Pistons are the best Std. Size in our opinion.
              SBT Tech Support is here to help with your problems.
              We try to answer each question quickly and accurately.
              Please do not use Private Messaging for Tech Support, use the forums.

              Comment

              • #8
                Just to clarify, you can do the test as you described with ANY cylinder in the uppermost position? Or is this only the #1 (mag) cylinder at TDC?

                I'm going to check a little further to make more precise measurements.

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                • #9
                  Any.
                  SBT Tech Support is here to help with your problems.
                  We try to answer each question quickly and accurately.
                  Please do not use Private Messaging for Tech Support, use the forums.

                  Comment

                  • #10
                    Hey Showme...

                    When I bought my '94 slt750, it had the exact problems you have now. I ended up buying an OEM piston from Polaris, honing the cylinder, new rings and sending the crank off to be rebuilt (twisted). By the time I was done spending money (I did all work myself, except crank rebuild) I would have been better off trading in the motor for a rebuilt unit from SBT. I am not trying to plug SBT, just my observation having been there, done that. Let's don't even talk about the time spent.

                    BTW, the replacement OEM piston is performing fine with excellent compression numbers compared to the others.

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                    • #11
                      I agree, start fresh with a 1 year warranty.

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                      • #12
                        Oh I'd do the SBT route too if it comes to that, and if I plan on keeping the boat. But I think I'm going to move on to a newer, faster level at this point. Not worth plugging $1k into a boat that my son and I have advanced past in abilities.

                        Still haven't confirmed the crank condition, not ruling out my bad setting on the carb yet.

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                        • #13
                          Sorry about the bum luck.

                          :( Is your engine an SBT? If so, you might be able to rule out the out-of index crank thing to a low possibility since they weld and true them @ the factory.

                          Which cyl is it?

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                          • #14
                            oh my.... advanced past in abilities? or advanced past stock form?

                            One thought... Tweek it, it'll give you a hard-core work-out for less than a new ski. But it won't have that "new car smell".

                            ;)

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                            • #15
                              Skexies - I'm not quite sure what you mean there. What I'm saying is it can't be good for a motor when you are full-throttled all the time when riding. The SLT is a very forgiving boat on rough water.

                              By the way, I checked a little more carefully on the crank twisting issue. Seems to be lined up properly - I'm reverting to my original thinking that I had a carb setting or clogged carb problem.

                              Still going to get it going and sell it though. I want more power to throw my money towards. [img]graemlins/evild.gif[/img]

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