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  1. #1
    can't leave nothin' alone! scrappy's Avatar
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    another dead 800

    My XP's topend is toast!
    I had it out last weekend and it was cutting out and dying in the midrange. WOT it was fine and it wouldn't idle in the end. I pulled the sparkplugs and the Mag cylinder plug had the side electrode pinched up against the center electrode and looked like it was aluminum grey. the PTO looked good. Yesterday I pulled the head and it looks like someone threw gravel into the cylinder @ WOT! the upper ring is exposed about 1/2 way around the piston and about 1" of the upper piston ring is gone. The head is scarred up to match the piston. Tonight I pulled the jugs and the piston is all scarred up on the pto cylinder and the mag is slightly scored too.
    So now I get to replace the whole topend! My question is can I have the old jugs bored or do I need new? The Mag piston is marked 82.14, is there room for a bore and bigger pistons? Are the domes removable? they don't look to be removeable to me.
    I "think" this is all due to the carbs being dirty and needing rebuilt and running the engine lean?


  2. #2
    96XPSS's Avatar
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    The pistons you currently have are once-over OEMs. Yes, they can be bored larger, I recommend ProX pistons as you have to go aftermarket now. It could have been piston pin bearing failure also. But I would most definitely clean the carbs while doing the top end. Shoot a pic of the rods and post it up too, need to make sure the big-ends are ok.

  3. #3
    flyin' the friendly skies airbornexp's Avatar
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    I think that you are going to have to shave the RAVE valves down too if your going that large...

  4. #4
    can't leave nothin' alone! scrappy's Avatar
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    I know about shaving the raves, I think I remember reading that they have to be shaved with a 1mm overbore. I probably should see how much my cylinders need bored out before I order pistons. the cylinders look good but I can feel some scoring with my fingers.
    96xpss, are you talking about the cranshaft end of the conn rods? how far down do I need to tear this thing? doesn't the crank need to be pressed apart to look at the crank end of the rods?
    the piston end rod bearing feels a little rough but is free, I will be replacing those bearings when I do the pistons.
    as to the carbs I have done some disassembly but can't see anything definitely wrong with them. but I am going to rebuild them anyways.
    with the scoring on the skirts that I have, I am starting to lean towards an oiling issue. I don't see how a lean issue would cause my piston skirt scoring. Are these pistons known to expand to the point of cylinder wall interferance when they get hot?
    I am going to pull the pistons off tonight.

  5. #5
    flyin' the friendly skies airbornexp's Avatar
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    post some pics of the pistons when you get a chance

  6. #6
    96XPSS's Avatar
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    The big-end of the rods can be seen now that you have the cylinders off, no need to go further. Rotate the crank so they are up and exposed for each pic. Discoloring on the rod means the bearing is about to fail.

  7. #7
    can't leave nothin' alone! scrappy's Avatar
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    here are the pics I took:
    the rod pics will have to do until I can get better light tommorrow.

    pics 1,2,10, & 11 are MAG
    pics 5,7,8 & 9 are PTO

    the PTO rod end bearing seemed dry and also seemed like they are discolored/rusty, the mag bearing looked pretty good
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  8. #8
    PEST!'s Avatar
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    Those pins look pretty bad and with that much metal flying around I would recommend a rebuilt crank... Looks like it had a lot of moisture in it..

  9. #9
    96XPSS's Avatar
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    Quote Originally Posted by PEST! View Post
    Those pins look pretty bad and with that much metal flying around I would recommend a rebuilt crank... Looks like it had a lot of moisture in it..
    +1

    I'd say the o-ring failed on top of the sleeve (from an overheated engine), or the exhaust manifold gasket starting spewing water inside the port.

  10. #10
    can't leave nothin' alone! scrappy's Avatar
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    Quote Originally Posted by 96XPSS View Post
    +1

    I'd say the o-ring failed on top of the sleeve (from an overheated engine), or the exhaust manifold gasket starting spewing water inside the port.
    the rods have light surface rust on them. The sleeve o-ring looks good but it seems to be work hardened/crushed.
    I didn't see anything wrong with the exhaust gasket.

    If I have to re-build the crank this thing is getting scrapped for a 4stroke of another brand(conversion)!
    MPEM blew the diode last summer and sat all summer long. I finally got that fixed in the fall and was able to get a about 10 hours on it and this happens within 3 hrs this year. I seriously doubt in the time I have owned it that I have put 20 hrs on it!
    I am not going to dump $1000+ into this thing unless I know can get a RELIABLE ski! This thing is NOT RELIABLE AT ALL with this EXPENSIVE Crap Bombardier uses! The only thing that might be decent is the hull!

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