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  1. #1
    sdlvx's Avatar
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    crankshaft big end bearing failure

    Today was not a good day. Went out on the black pro, rode kind of hard for a while, then idled down to like 20mph to catch my breath. I go to get back in the throttle and it slowly dies down. Go to start it again, just a thunk like it's hydro locked.

    Come back and pull the top end off, the front piston and head have lots of dents and chunks of metal. Pull off the jug and there's gold metal shavings and the bottom bearing is locked, you can tell it got hot. The other two look great and spin fine.

    Not sure what happened, it's a new crank from crank works, only one real season on it. It is a stroked 750 crank from the previous owner and crank works losing his 785 crank. I run premix 44:1 klotz skicraft, stopped using the stuff with the benol a while ago.

    Did I do something wrong or was this a bad bearing or bad clearances or something?

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  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Are the other connecting rods that same color? It almost looks a little rusty.

    I remember there being a problem with water in the collector and running back into the engine when pulled up a steep ramp or hill.

    Only other thought I can think of is too tight of clearances when everything heated up and expanded or Chinese made bearings.

    I'd like to see what Crankworks has to say.

  3. #3
    sdlvx's Avatar
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    The other rods and bearings look fine, nice silver color with the bearings spinning well. It is set up the watcon way with a check valve going to the pipes. Maybe I did lift it up too far at one point?

    I wanted to get some opinions before I call crankworks about it. Could be a chinese bearing, the rods were replaced, this is the problem Pro I bought off the horrible guy from PWCToday who thought the crank was done wrong, after CrankWorks lost his crank and then sent him a stroked and done up 750 crank.

    There are no SBT markings on the rods I believe, I'm away from the ski for the next few days, but I don't know what kind of rods or bearings they put in there. I know SBT usually isn't well received but it seems like there's something else on this crank, which I don't understand because I thought SBT was the only place to get Pro 785 rods. Unless this crank was done a while ago when Hot Rods was still make pro 785 stuff, which could explain it because I noticed searching this forum Hot Rods had lots of problems.

    I have been unusually busy this year, it was only my third time out on it for the whole season, first two times it ran great. And getting rid of the Klotz with castor bean made it possible to read piston wash.

    I can't remember, is the mag cylinder the lowest pipe to come out of the collector? I have a habit of lifting them up to drain the water out of the back of the hull, maybe I did it too much one time?

    At least I'm so proficient at fixing these things I had the whole top end and two pipes off in two hours.

  4. #4
    johnsonmtz's Avatar
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    I'm not seeing any wash on the dome of that MAG piston so I'm wondering if that cylinder went lean. Usually that results in a holed piston, not bottom end bearing failure. But, if the tolerances were just a little close on that bearing, the reduced lubrication might be enough to get it hot and cease up.

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Just did a quick peak and the CEN pipe is the lowest one of the 3.

  6. #6
    sdlvx's Avatar
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    I just had a bad thought, the idiot I bought this from thought the mag end of the crank was wrong and the timing was all off. I hope he did not do something like try and beat the mag end to "fix" it in his own special way.

    If the center is the lowest I would think that would be the first to get water if I tilted it up too far.

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    All that little gold flake makes me think it was the connecting rod wearing away. Before SBT came out with rods for the 785, I think shops had to machine down sled rods to work. I wonder if those are what you have?

    I actually looked for the bulletin about the pro and water running back on steep hills, but came up short. I only found it to be an issue with 1997 model year and didn't specify which cyls would fill up. It just said it had a problem with it happening.

  8. #8
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    In my opinion, I think the motor fell due to mismatch of potentially low quality parts. Crankworks has done all of my cranks (now 3 of them) and they have all been damn near spot on in terms of run-out and phasing.

    I have the 785 SBT rods in both my limited and superstock ski. The superstock has seen 8100+ rpm for now 3 seasons and they seem to be holding up well. I did source OEM main bearings an used the SBT crank pin bearings on both. The unfortunate thing is that nobody really has any idea what bearings were used in this crank. I cringe at the fact they had to "stroke out" a 750 crankshaft to replace a lost 785 crank. If I recall, the 785 has different rod part numbers for the MAG / CEN versus the PTO with the difference being the crank pin length. I know your MAG let go but I just wonder if that crank was really the right one to have in that motor.

    This all being said, I'd try and find a core 785 crank and have it rebuilt to get this ski back to how it should be. You've definitely gone through a lot with this ski and I'd hate to see you give up on it now.

  9. #9
    sdlvx's Avatar
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    I should get the cases apart in the next few days to get a better look. I won't give up, I'm not a quitter. Oddly enough I worked so hard to keep my other one as stock as possible and I always get compliments on the black one. Maybe today if things go well, I don't know.

    There were small metal chunks, it is almost like a bearing came apart.

  10. #10
    sdlvx's Avatar
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    Alright, I finally got this thing apart. Whatever is up with this crank is not good, the outer mag bearing just fell off when I took it apart.

    The bearing looks like it just disintegrated. This poor thing has been blow up a lot, the crank cases all have lots of pitting and damage but it's been there for a while.


    Here's where the bearing was that just flat out fell off when I pulled the crank out



    I'm guessing this crank is just garbage, maybe a good experience for me to learn how to disassemble. I have to say, looking at the inside of those cases, this has happened to this ski, a lot.

    Looks like the bearing just gave out completely. What a disappointment, but I feel like that one bearing falling off makes me think this is on Crankworks. That doesn't seem right, it should press on.
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