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pistons keep smashing pistons, but its all OEM!

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  • pistons keep smashing pistons, but its all OEM!

    hi my name is Tony Underwood and i live in the south west of the uk.

    last summer i managed to melt the plastic part of the exhaust on my xp. not noticing that this had occurred, my jet ski filled with water, and very nearly hit the bottom of the deep blue sea.
    it wasn't until the engine came to an abrupt stop, that i realised something was wrong.
    after being rescued i immediately flushed out the water and prayed..........

    7 days later after replacing all melted exhaust parts etc, i took the machine out on the water again..
    after about ten minutes of splashing about she decided to throw out the big ends, which as you can imagine, took out the pistons and any thing else it possible could of!

    over the next two weeks i stripped the xp and decided to build her good as new........
    new crank, pistons, etc etc......
    finally got the parts shipped from the US and began to rebuild the mighty beast.
    bearing in mind that my 98 model xp ltd had only done an incredible 21 hours from new!!!!!!!!!!!!
    after rebuilding her and re installing the engine, i had to work away from home so there was about a 60 day gap before i could start and test the xp.

    when starting her, she sounded fine. but being Mr butter fingers a dropped a bolt under the exhaust, so i had to remove the exhaust to locate it...........

    that's when my disaster struck.... when removing the exhaust, i found new pieces of pistons and rings in the exhaust ahhhhhhhhhgggggggggggg.
    i believe what has happened is that the rave valves have some how, hit the pistons and knocked off their tops taking the rings out as well.
    ive asked many jetski centres and other technically minded people how this could have happened, but ive only received negative answers and may people scratching their head!!!!!!!!!!!!!!!

    could my problem be common?
    have i done something wrong?
    is the crank defective?
    who knows the answers to this except god!

    all i know is.
    if my machine had, had the recall for the air filter, i believe that this would never had happened in the first place.
    but whets more of a kick in the teeth is that i must be the only person in the world, who has managed to blow a jet ski up, on the trailer and in the garden.
    also now i have the problem of why why why ... and what to do!

    if you have any advise i would forever grateful, because i and many others are eagerly waiting some answers, that are logical and practicasl.


    please help a fellow lover of the mighty SEA-DOO and make my life complete again

    many thanks
    Tony Underwood

  • #2
    From what you have said in private email, specifically that you rebuilt it with standard size pistons, it doesn't sound like you are actually experienceing ring snag from the RAVEs. I would be more suspecting lean detonation, which to the uninitiated, could look like chipping from the valve. Is there any way you can send good digital shots of the piston tops, sides and cylinders?

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    • #3
      the pistons break arter about 30 seconds of running! do you think thats long enough for detenation to occur?
      thanks
      tony underwood

      Comment


      • #4
        Unless you have broken RAVE shafts, allowing the valves to protrude deeper in the slots, or are using oversize pistons, there's just no way that they are hitting.

        This is assuming we're not overlooking the obvious like they are in upside down...the side with TOP printed on them goes up.

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        • #5
          thanks,
          hopefully im not a big dum *** , and have done the unmentionable, but surely i couldnt have!
          will they fit and look normal upside down?

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          • #6
            You know, I don't even think it would make a difference as to less clearance, if they were upside down - I think the clearance would actually be even greater. They are angled to conform to the cylinder, not the piston.

            No, 30 seconds at idle would not be enough time, unless there was something seriously wrong like WAY off timing or WAY high compression, to get severe deto damage.

            If you can't provide pics, can you fully describe the pistons tops, sides and cylinders?

            What EXACTLY did you do for the rebuilds? I know you mentioned - 'cleaning up' a set of pistons? What is your piston to cylinder clearance? Did you hone, bore, or re-sleeve?

            Comment


            • #7
              to be honest, i dont know how the pistons look now,because after i rebult it from scratch and then it blew the pistons, i simply handed it to my mate who is actually a better class of technician than me, although exactly the same thing happend to him, huuummmm!BANG........
              when i did the first rebuid i changed the crank, both pistons, rings, pins, all bearing and small end.. i had the bores honed cos they were still pretty good. i had the head not skimmed but cleaned but skimmed. if you know what i meen! all new gaskets etc. i replaced all the parts inside the rave, because i left them to soak in detergent and all the rubber parts expanded to the size of an orange (easy mistake).
              you mentioned the timming! 'could i have put fly wheel on wrong? if i remember correctly there was some sort of lump on fly wheel that had to go at the top, (memory is a bit cloudy, sorry)
              i have a shop manual and if i got stuck (which wasnt really very often) i religiously read aqnd followed the instructions it gave!
              what do you think? have i and my collegue have both messed up??????? possible i know!
              thanks ................. [img]redface.gif[/img]

              Comment


              • #8
                Well, I would say that it's no coincidence that both engines built by the same guy blew in the same manner. Something was not right, that's for sure. For all you know it could have been a poor hone job, and piston slap, or the piston on backwards.

                To align the magneto cup, place the flywheel so the hole is at 12 o'clock, and the two large holes are at 2 and 8, with one of the magnets directly lined up with the flywheel hole.

                [ June 24, 2001: Message edited by: Bryan Glynn - SBT Webmaster ]

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                • #9
                  thanks for all your help!
                  i will look all these posible hicups this week starting with upside down raves and then upside down pistons etc.
                  can you ship parts to the uk, as i was using parker yamaha in arizona, but they are really expensive, and ive replaced to many pistons already to be paying big bucks again!
                  if so please e-mail me with address etc..
                  thanks again tony underwood.

                  p.s
                  Awsome site. [img]smile.gif[/img]

                  Comment


                  • #10
                    Unfortunately, we do not sell parts. Try Bill O'Neil at www.watercraftmagic.com

                    Comment


                    • #11
                      OK, I verified here at the factory that even flipping them upside down will NOT cause this to happen, as I thought, the clearance is actually EXTENDED by doing so.

                      The 951 valves will have two stamped part IDs on them, on the top side. The bottom side is blank. The 800 valves, are stamped with TOP.

                      [ June 25, 2001: Message edited by: Bryan Glynn - SBT Webmaster ]

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