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  1. #1

    Causes for overheating in the water and how to monitor temps with the D-plate.....

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    Last edited by Emig5m; 03-29-2011 at 08:02 PM.


  2. #2
    Forgot to ask, my father who was working on it said that the powervalves where gummed up and not moving freely at all! (but they're now cleaned up and moving perfectly free). Could gummed up or stuck powervalves cause overheating?

  3. #3
    WAVEATER WAVEATER's Avatar
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    You said it was"possibly heatseizing and finally blew up". Did the motor drag itself down as you were running and did you check the pistons on tear down? The piston or pistons will show seizure marks on 1,2,3 or all four corners, just ahead of and behind the piston pin opening's. Thats a piston getting hot, expanding and then sticking/dragging against the cylinder walls. You wanna make sure that the cause is overheating and not something else, or it will be a repeat performance. melting down the exhaust side is a lean condition, dished on top and then melting down the exhaust side is a detination problem and evenly scored all the way around is a lubrication problem.

  4. #4
    Here's the last time it went (badly damaged piston on the right of the first pic, previous piston on the left - both from #3).....























    The totally smoked piston is a brand new piston (about 25 minutes on the build) that replaced the previous piston (as pictured next to it). Both are from #3 - I have no pics from the other cylinders.

    Basically it will start up and idle perfectly fine. Run good on the hose but once out on the water it will just bog out of nowhere, stall, and then it seems like it's locked up because the starter won't even turn over the motor. Leave it sit for about five minutes - it will start right up and continue the process. If it was a leaky crank seal, wouldn't it idle erratic? It will idle perfectly non stop forever. Lean? This thing is the smokiest 2-stroke I've ever seen! Which mine smokes just like all the other ones you see on Youtube. None of my 2-stroke MX dirtbikes ever smoked like I see these GPRs do!

    Does either of them two pistons from #3 tell a story by looking at them? Also, I noticed the battery was almost fully dry but it was starting the ski. Does the battery play any role of the computer functioning properly?

  5. #5
    WAVEATER WAVEATER's Avatar
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    Looks like the first piston was definately getting hot but not from a cold seizure but rather a more gradual heat up, course how hard you drive it right after start up would dictate how fast it heats up too. The four corner scars I spoke of are characteristic of a cold seizure. The starter not spinning for a few minutes is a very good sign of a overheated piston stuck to the cylinder walls. The second piston is so hammered from debris etc. that i can't make a guess as to what happened to that one at all. I saw one last week that a guy rebuilt himself and he had installed the piston backwards, the ring keepers and open end of the rings were facing the exhaust and after about 15 minutes run time the rings caught the exhaust port and 30 seconds later his piston looked like yours. Not saying thats what happened on the rebuild just throwing one of many things that could have happened out their. Maybe a piston pin clip wasn't seated properly and popped out and started hammering things, their are marks on top of the piston that are characteristic of a clip banging around in their, (those same marks could be pieces of the top ring flying around to). But judging by the pics it looks like the clip is in on the one side and I am assuming the clip was removed on the other side when pulling the pin. All you can do is rebuild again and carefully inspect the cooling system from intake to outlet checking for sand dams, kinked hoses etc. If you have a shop doing the build tell them you want them to run it themselves for 30 minutes after they finish the build, so if they screwed up the build in anyway the bomb goes off in their hands and not yours, it keeps your wallet from getting emptied again. Of course this means out on the water under load, not on a hose with forced well water and no load or RPM's. Anyway the second piston is so messed up I can't tell if it was a repeat overheat or an error in the rebuild. The leaking crank seal you questioned would cause a lean condition and likely burn down the piston closest, the piston would be melted starting on top of the piston and melting down the exhaust side, this is not what happened on piston one and piston two is doubtful as well. It might idle a little higher with a leaking crank seal but two cylinders are operating close to normal so unlike single cylinder motors crank seal issues arent as noticeable, and anyway the PTO end has 2 seals and the Mag end has one but the stator housing is sealed as well or their would be water intrusion on the stator. Of course whenever you have a some sort of mechanical failure, replacing the failed parts doesn't "fix" it, you always have to determine what caused the failure and fix that to. A close to dry battery won't effect anything in the copmuter that I'm aware of, I see lots of dry batteries without any running issues, just a trashed battery.And yea she will definately smoke more than your MX cause your comparing a three cylinder to a single cylinder. Line up three MX's and then you have the smoke put out by your GPR (roughly anyway lol). Oh yea, I put in the "D" plate before I even lifted the machine off the factory crate base and did not replace the temp sensor with the resistor and have never had an issue, I have the 07 fuel injected 1300.

  6. #6
    Quote Originally Posted by WAVEATER View Post
    Looks like the first piston was definately getting hot but not from a cold seizure but rather a more gradual heat up, course how hard you drive it right after start up would dictate how fast it heats up too. The four corner scars I spoke of are characteristic of a cold seizure. The starter not spinning for a few minutes is a very good sign of a overheated piston stuck to the cylinder walls.
    Ok, this is exactly what I thought, now I have to find out why it's over heating and heat seizing. Like I said, it runs ice cold on the hose and runs for ever without a hitch and doesn't even get warm. When I first got the ski I could of sworn that the fuel filter was never more than half full and the fuel switch sometimes feels extremely tight to where I almost cant turn it. I put some fuel system cleaner in the gas and kept turning the fuel switch to loosen it up and for some reason the filter fills right up to the top now!?

    I had an issue once with a dirt bike that was steel sleeved from the factory plated cylinder (95 KX100) and low and behold it kept heat seizing on the stock jetting. Upped the main jet two sizes and it ran perfect forever. The cylinders on this ski have been sleeved from the factory plating and I'm wondering if the jetting has to be fattened up top for the steel sleeves like my bike did? I know my dirt bike did the same thing, heat seized and totally locked right up. I thought it was dead, but by the time I pushed it back home down the tracks it would cool down and loosen up and kick over and run again. Once I upped the main jet, bike ran flawlessly for the next two years I owned it.

    Now on the piston that's ate up, could a powervalve touching the piston do that? I remember seeing the pistons before the head was put on and all the arrows where pointed correctly. The last time it was taken apart, I noticed the powervalve on the cylinder looked dangerously close to the edge of the cylinder wall compared to the brand new one (new design) I put in #2 so all valves got cleaned (they where gummed up and very sticky) and all got shaved down with a dremel to make sure there was no piston touching, lol. My father who was the one working on it said that the new OEM circlips on the piston pin where much thinner than the ones that came out of it - he's since put that old piston AND the old and fatter circlips back in (and compression measures (115#3 115#2 which is a brand new OEM cylinder & piston and 118on #1)

    I've read that once the D-plate is installed that the factory jetting is dangerously lean in the midrange and could cause a seizure? Could this also be the problem? I noticed it seems to run good at all throttle positionings except for absolute WOT where it seems to stop pulling ever so slightly but just barely letting off the throttle just a tiny bit it seems to pick up a little and pull harder. Or maybe that was the gummed up powervalves? (hasn't been ridden since the valves have been totally dissembled, cleaned and freed up, and modified with a dremel so that there's plenty of clearance to the piston and not dangerous close - the new style updated valve looked much farther away from the piston/inner cylinder wall than the old style so that's why the other two got the dremel treatment).

  7. #7
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    The sensor you bypassed and put the resistor on has nothing to do with the water temp it's for the exhaust temp, The water temp sensor is on the bottom of the stinger pipe.

  8. #8
    Quote Originally Posted by JIM'S PERFORMANCE View Post
    The sensor you bypassed and put the resistor on has nothing to do with the water temp it's for the exhaust temp, The water temp sensor is on the bottom of the stinger pipe.
    Oh ok, so my water temps must be good then if the alarm isn't going off? BTW, for some odd reason my father cut those wires when he took the motor apart, are those wires polarized? (both are black so he figured they aren't polarized) Wonder if I should get a new water temp sensor because wouldn't you figure if it's getting hot enough for a heat seizure shouldn't the temp sensor throw the alarm or whatever it does when it detects overheating?

    I don't know what to do with this ski. Since I've been riding recreational vehicles since 1988 I've never ran into such a troublesome motor as this GPR is.... what the hell is causing it to heat seize? Fuel delivery maybe? Is there a way to fatten up the jetting without taking the carbs apart and installing different jets? Maybe I could cool it with liquid nitrogen....shouldn't overheat then, lol... I feel like putting it in the water tomorrow and just holding it wide open non stop and beating the hell out of it and if it blows again, just drop a match in the gas tank and let it burn... I'm so fed up with this thing!!

  9. #9
    well maybe watercraft isnt for you... good grief...

    if you start by building the engine correctly with matching parts, pressure testing for no leaks, rebuild the carbs, fuel lines etc and go thru it all since you have such a basket case, along the way you look for anything obvious, any blockage etc, if not and all is good on the motor end, fire it up and go from there... you are chasing your tail trying to troubleshoot what was...

    if the case/engine hold pressure and fuel/spark is right it should run...

    having that bag of mixed crap before did not help and difficult to diagnose...
    you cut the wires why??? that water temp sensor is ohm sensitive... now you`ll need another or chip that as well and that info is here on how to do that...

    these 3 cylinder engine run hotter period... the efi ski`s are leaner from the factory.
    there are also specific threads on carb rebuilds and jetting if your worried and want to fatten them up...

  10. #10
    Quote Originally Posted by Pale Rider View Post
    well maybe watercraft isnt for you...
    I bought a used 94 VXR 650 and put over 90 hours on it this summer since July 9th which is 226 gallons of gas and not one single glitch! Never even took it out of the water all summer and left it tied to mooring bouys! Still measures at the factory 150PSI per cylinder and everything! Fires right up without even using the choke. It's the GPR that isn't for me and not watercraft! I love my VXR, it cost only $800 with the trailer and I can jump right on it and use it! I'm into this GPR $5200 now with buying brand new parts and only have less than an hour of use out of it!!!

    This forum came highly recommended to me. I was told that there was a lot of GPR gurus here. But heck, I'm trying everything, what else can I do? I'm 100% exhausted on ideas!

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