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# 1 Hole in the Piston

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  • # 1 Hole in the Piston

    Ok guys so tell me this... Last August (2000) i bought my 94 SLT 750 ski with a bad motor. Bought the SBT motor and rebuilt the carbs, jet pump, and replaced the driveshaft with the new updated polaris one. I installed the second fuel pump and plumbed it into the system as SBT told me. I also did the mixtures on all three carbs and got the correct high and low speed mixture settings so that the machine wasn't lean. Now today she just turned 38 hrs and I am faced with a hole in the #1 piston after doing everything I was told on here. I know I could be an idiot and just put a piston in and chance my luck, but from my readings here, that is the worst idea yet. :( So i guess my next question is I know that I am out of my warranty by one stinking month, but will SBT help me out at all on this or am I just screwed? This machine has given me so many frustrations and I've tried to do everything to keep it and me happy. I am now also pushing the limit as to what it is worth as well... Any suggestions Brain or others? I appreciate all of your help but I can't take this anymore! Neither can my wallet! [img]graemlins/spit.gif[/img] [img]graemlins/crying.gif[/img] [img]graemlins/angryfire.gif[/img]

  • #2
    If you went 38 hours, I'd say you had something happen, like trash in the carbs, bad gas, wrong plugs, blocked cooling, etc.

    If it's one of ours, we can repair it for you - just give Joe a call @ 877-330-0231 and let him know what happened.

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    • #3
      Yeah, I was out all day Saturday no problems till the end of the day when it started acting funny, so I pulled the plugs and checked them... All seemed well. So I put her back in yesterday and she run fine for about an hour and then thats it... I heard that I had lost compression in #1 piston.. So i pulled the plug on the water and cranked her over... Sure enough no compression.. So after getting towed home by a Sea-Doo I pulled the head and saw the nice hole in the piston. Do any other of these PWC manufacturers have problems like this?

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      • #4
        Sorry to hear of your frustrations. I can assure you that this doesn't happen all the time. You are also wise to heed everyones advise on not just replacing the piston. Do you know for sure that there is a hole in the middle of the piston by a visual inspection?

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        • #5
          No, they don't. Most have much better cooling capacity in general.

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          • #6
            Check your fuel seperator carefully, look for water contamination. Look in the bottom of the bowl. If you see a little bit of brown stuff in the bottom of it, then you have algae growing in the fuel. This stuff can get by your fuel filters, and plug up your jets. Only option is thorough disassambly and cleaning of the carbs. You will also have to get some diesel biocide and run it in the gas for a couple of tanks to kill the grunge. You might also want to check the fuel tank filler cap and make sure that the cap or threads isn't broken and letting water into the gas. LOL
            <a href="http://www.wetwolf.com/" target="_new"><img src="http://www.wetwolf.com/images/hurrsigpic.gif" width="400" height="100"></a><br /><br />Bruce Wolford<br />Wet Wolf Technologies - Purveyor of Performance Pump Parts<br />(509) 280-5444<br /><a href="http://www.wetwolf.com" target="_blank">Wet Wolf Tech</a><br /><br />PWC Race Director<br />Northwest Water Competition<br /> <a href="http://www.nwh2oracer.com/ijsba" target="_blank">http://www.nwh2oracer.com</a>

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            • #7
              Thanks for that reply wet wolf... My fuel is water free and fine... Ok so Brian I have taken the motor out and taken some pictures... I sure hope you guys can help me with this thing... Brian - can you show these to Joe so he might be better informed when I call (if necessary)? The piston as you can see obviously got hot and melted the half side of the piston around the plug up top. However I was surprised to notice that the bearings of that particular cylinder looked fine and I could not trace any of the aluminum down at all during the tear down of that cylinder. I have not and will not do any furthur disassembly of nothing else until I talk to Joe. Thank you all... I think I feel a little bit better now.





              [ September 19, 2001: Message edited by: Bryan Glynn ]</p>

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              • #8
                A bad batch of gas can cause this too. What I find odd is that the underside of the piston crown is clean. Normally there would be black deposits from getting really hot and burning onto the underside. The lack of carbon on the underside leads me to believe that this happened really quickly and not through some time. Maybe you have some carb blockage or fuel blockage? Where you using BPR7ES plugs? Did you buy your gas from a name brand station?

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                • #9
                  Sealion - I will inspect the carbs tonight, but I believe it happened very quickly as well because the day before this happened the machine ran for about 4 hours strait no problems, no power loss. no hesitation, etc. I always run Mobil or Sunoco Premium 93 unleaded and thats it. Never no-name gas stations ever. Also, the plugs were BPR7ES and the mixture prior to this was on the money.

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                  • #10
                    I made them available in your post. He'll see them if he needs to.

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                    • #11
                      etbtsi, Could be one of the fuel pumps too? Check the T's from the pulse lines. Maybe not enough pulse because 1 line is feeding 2 pumps? Check the fuel petcock. They can go bad and block proper fuel supply. I personally run 2 pumps but with 1 pulse for each pump (had to install an extra pulse fitting). I also bypass my fuel petcock. One more thing that comes to mind. Did you run out of gas while maybe going full throttle? It's best to run on reserve if you keep the fuel petcock and fill up when you get down to a 1/4 tank.

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                      • #12
                        While one pulse line per pump is always best, the stock 750's provide more than enough pressure to drive two small pumps off the stock line.

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                        • #13
                          Sealion - I will look into that after I get the engine back.. I talked to Joe today and he is sending me up some paperwork so that I can ship the engine down to SBT to have them inspect it. Hopefully they can help me out and I can get this thing back together and in the water for next season without breaking the bank! Thanks to all for your help. [img]smile.gif[/img]

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                          • #14
                            Your problem could also be timing; crank out of index, flywheel problems and even stator problems and i can tell you this: OHMS check on the stator are only maybe about 30 percent right, I have replaced alot of stators that tested good and it solved the problem, but there is alot of posibilities with polaris motors, believe me i know, i have seen every problem with polaris motors and then some, some times polaris calls us for advice.

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                            • #15
                              Ok... since the whole thing is apart I will check that stator out. What pins do I need to OHM and what should there respective values be ? Also I don't know how you deal with this polaris motors! You must need many cases of beer throughout the week! :D Thanks

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