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  1. #1
    Hexec's Avatar
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    Can use some advice on 1st xl1200 PV rebuild

    Well, I have began my winter project. A friend of mine blew a hole in the upper crankcase. I took on this job to save him some money. Besides, if I didn't, I lose my riding partner....lol Who likes to ride alone? We pulled the motor out of his 2000xl and I began working on disassembly just before xmas. I wanted to assess the damage and begin sourcing parts. Here's what I found once i had the motor apart.

    1) We already knew about the big hole in the upper crankcasing.
    2) Cylinder wall that extends into the case was broken.
    3) The wing portion of the piston was broken.
    4) Reed valve end stop in the front intake was bent.

    I managed to find a good used crankcase ($400 shipped to Canada). Case came with all 3 reed valve assemblies still in the intake. I still need to find a front cylinder and piston. It's clear to me that something inside collided with the crank and the bottom of the cylinder/piston. The cylinder pieces found their way between the crank and the casing and pushed the pieces out into the hull. There was not much metal pieces in the casing. Almost everything was in the hull. Anyway, my question right now is how could this have happened. I want to be able to correct the condition that caused the failure. Not just replace parts and hope it doesn't happen again. BTW, compression in the front cylinder was lower than the other 2 (80, 120, 120). The piston rings were worn on one side of the piston.

    Any help/advice is much appreciated.

    Thanks
    Mario


  2. #2
    xxx2's Avatar
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    You need to clean the carbs paying attention to the affected cyl. especially. I also would look into installing waveeater clips on the p/v and install a d plate in the exhaust. If the crank looks discolored like it got hot you may want to check for play. You may also check the the oil lines as they have a habit of popping off from hardening/being to short.

  3. #3
    My guess is the engine may have previously water-locked in the jug with only 80psi. Possible cause is the ski sunk, a water passage blew in to the cyl, possibly incorrect operating procedure on the hose, or just dumb luck.

    Hydro-lock could have possibly bent the connecting rod which lowered compression down to 80 for awhile.. Look for signs of piston skirt smashing the crank to be sure as if the rod bent enough it would have caused the piston to interfere on the down-stroke and smash into the crank. This caused the piston skirts to severely weaken and (eventually?) fall apart and down into the case.

    If this is the case then you need a new crank (Probably goes without saying actually). She might have run for a bit with a bent rod until total destruction.

    /snip/

  4. #4
    Hexec's Avatar
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    There was no sign of a bent piston rod. The crank looks in amazing shape with no discoloration what so ever. The oil lines were all in place. And the ski was never water locked. The ski run for a couple years like this without an issue. The ski is never abused. We're not thrill riders. We just take the kids out every weekend on lake Ontario. 5 minutes (last run of the year) on a slow cruise speed, the engine clunked and stopped. He was able to start it back up but didn't last very long before it died again. I towed him back to the ramp at no wake speed. Not sure what the carbs have to do with this sort of failure, but of course I will check for any blockages. Ski never run hot, pisser on the side was shooting water. And ski was able to hit 90KPH (56MPH) with good acceleration before this run.

    The only thing that I can think of is the power valve resetting too deeply into the cylinder. With the piston sitting on a slight angle due to the worn rings, the piston skirt contacted the power valve on the down stroke. Then the pieces took over and created the rest of the damage. Again, I was amazed that the crank is in such good condition. The other think that I find amazing is the cylinder wall doesn't look that beat up. If it wasn't for the broken skirt(wing) at the bottom of the piston and cylinder i would bet that new rings and hone will bring the compression right back to 120. I'll try to post some pics.

    Anyone know of where i can find a good used cylinder and piston?

  5. #5
    Hexec's Avatar
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    btw, it looks like the exhaust already has a D plate, I don't see a catalytic converter. I need to look into what waveeater clips are. thx

  6. #6
    when you bought the case did you buy a full matching set? They are specially machined mating surfaces that are matched together. people on here will say you can use one side or the other but you really shouldnt make sure top and bottom are a matched set!

  7. #7
    Hexec's Avatar
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    yes, it was a matching set. That's a really good point.

    ok, I see what waveeater clips are now. The fact that these clips exist sort of tells me that my theory might be what happened.

  8. #8
    xxx2's Avatar
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    The reason I mention to check at least the affected carb is if it leans out the piston gets hot and will swell up in the bore. The skirts of the piston are wider than at the crown of the piston will start binding all the while the other two non affected cylinders are pumping away causing the lean condition to worsen. The low compression before hand may have been from mild seizures of that cylinder IE. getting hot scoring piston/cyl....just something to check

  9. #9
    Hexec's Avatar
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    Thanks xxx2, will definitely be checking carbs. The strange thing about that cylinder/piston is that aside from the worn rings and the damaged skirts, the walls don't seem to be overly scored or worn out. Got to get some pics up. One other thing that I noticed in the power values. When we opened the covers. They were all filled with what looked like black/dirty grease. I would have expected that space to be unoccupied. Should it be clean and lubed with 2 cycle oil or should I refill with clean grease on reassembly?

  10. #10
    GGG's Avatar
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    If the exhaust valve dropped it usually pinches the piston rings so they get stuck in the piston and cause low compression. easy way to tell is to see if the valve is still there or if the end of it is all beat up. if your going this far, may as well go all the way. check the coupler to make sure its not rotted because if it is, the ski will take on water. rebuild the carbs with all the upgraded jetting and screw settings. wave eater clips. No real need to go premix unless the oil pump is rotted. clean out the gas tank, blow out the fuel lines, change the fuel filter and valve. all of this fuel system maintenance is because if it wasnt the reason the motor blew, it will be next time
    And clean all the sludge off the exhaust valves. That happens over time because Yamalube is crap oil. all that sludge is what causes the valves to drop

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