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  1. #1

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    1994 750SS - Needs top-end, have a dilemma

    So, here's the deal. My sister has a 750SS that's somewhat rough around the edges but not too bad; Faded graphics/stickers and handlebar cover, new mats and seat cover.

    We were out on the lake earlier this week and it went from a solid runner to poor compression in the front cylinder in the course of a couple of hours. I haven't pulled the head off yet to see if the cylinders are damaged or not. Before we went out, she checked her oil tank and I topped mine off on the Raider. For the same amount of riding over the weekend, my Raider used 1/3 to 1/2 a gallon of oil for 2/3 of a tank of fuel. That seems like a lot, but it runs great and I'd rather use too much than too little oil. Her tank went down by maybe a quart, which compared to my Yamaha seemed like not enough oil.

    So last time out she was riding and noticed that if she ran WOT it would fall on its face after a minute or so, but cruising around it was fine. Towards the end of the ride it was running rough, then once on the trailer it wouldn't start at all. Got it home, checked compression. Oof.

    Getting to the point, her plan before this happened was to clean it up and sell it and work on getting a 3-seater. This engine problem has thrown a monkeywrench into things. I can do the work to do the top-end, but the real question is...is it worth it? A 750SS in good cosmetic and mechanical shape isn't worth much to begin with, by the time she does graphics and the top-end is done she won't get much profit when she goes to sell it.

    Would she be better off cleaning it up and selling it as-is for a few hundred bucks? Could she get $400 if all it needs is the top-end? If she drops $300-$400 into it for top-end and fixing the cosmetic issues, would be be able to get $700-$800 for it?

    In both cases it sounds like the end result will be about the same, $300-$400 in her pocket if she's lucky.

    What would you do?


  2. #2
    Pain is fear leaving your body.... rlovebk's Avatar
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    Hmmmm.... You could buy mine for 750.00. Then you'd have 2 monkeys! LOL.
    See what parts Jon Zigler has for the ski if any. He now owns Watcon and has ran and owned Rock County Jet Ski or something like that for a while. He is honest and good fast service. (code for sends the crap you ordered and paid for right away)
    I will look for a link and post it. Just in case you don't have a parts source.

    www.rockcountyjetski.webs.com

  3. #3
    steve45's Avatar
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    Fixing up old 'Skis is no way to make money! Look at the 750s in my signature. I'd sell everyone of them if I could--and I'd only come out even on one of them.

    Without knowing exactly what wrong (and what caused it), it's hard to say what it would cost to fix.

  4. #4

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    Not trying to make money, just trying to lose the least money.

  5. #5
    steve45's Avatar
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    That's simple--buy one of mine!

  6. #6

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    So I pulled the head off today, being as this would be my first 2-stroke tear down it looks like there's some good news and bad news.

    Good news - Cylinder walls are virtually perfect. Front cylinder has a slight vertical groove that you can't see but you can feel. Suspect boring it 0.5mm will fix it up.

    Bad news - It looks like the rings in one or both cylinders have decided to break. The combustion chamber in the head and the top of the pistons have damage as if small chunks of metal have been bouncing around in there. The piston edge on the front (bad) cylinder has small chunks missing as well and there are donut-spreckle-sized bits of metal sitting on top of the piston. The rear cylinder's piston and combustion chamber show similar shrapnel-related dings but not as many. I've yet to pull the engine out or apart completely so I have no idea what bits of metal are laying in the bottom of the engine.

    The problem - With the damage to the heads and it being unknown what's laying in the bottom of the engine, I'm assuming this thing is going to need to be torn down and sorted out to make sure everything is kosher.

    This suddenly turned into more than I was hoping for or expecting. Almost feel like it makes more sense to just drop in a rebuilt engine considering I don't have a lot of time to work on this thing as it is, but maybe one of you can provide some light at the end of the tunnel. I was expecting just worn rings, not a catastrophic failure.

  7. #7
    steve45's Avatar
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    Don't panic, the bottom is probably OK. You'll have to spin the crank a few times and see if you feel/hear any roughness in the bearings. You can wash the crankcase out with solvent. After you pull the cylinders off, you can see if the pistons are scored. If so, probably too lean or no oil. If not scored, you probably just had a ring catch on a port or the piston just broke. These things need pistons/rings about every 200 hours or so.

    You can probably smooth out the head and re-use it.

  8. #8

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    Quote Originally Posted by steve45 View Post
    Don't panic, the bottom is probably OK. You'll have to spin the crank a few times and see if you feel/hear any roughness in the bearings. You can wash the crankcase out with solvent. After you pull the cylinders off, you can see if the pistons are scored. If so, probably too lean or no oil. If not scored, you probably just had a ring catch on a port or the piston just broke. These things need pistons/rings about every 200 hours or so.

    You can probably smooth out the head and re-use it.
    Thanks for the info, I did spin the crank by hand (while still connected to the pump shaft, etc) and it spun just fine, nice and smooth with no roughness or noise. Even with the pistons/rings the way they are there wasn't any scraping. The cylinder walls weren't dry, when I felt the cylinder walls with my fingers I did get a light coating of oil on them, but I don't know if that means much of anything. It'll probably be a couple of weeks before I can really spend any time pulling it out and taking it apart.

    Thankfully these things are pretty dang simple compared to a 4-stroke.

  9. #9
    steve45's Avatar
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    Actually, checking for a thin coating of oil is the way to do it. Should be enough to lightly stain a brown paper bag.

    I'd still look for parts in the bottom, and coat all the bearings with oil if you're going to store it for a while. Of course, cover it with a plastic bag to keep dirt out.

  10. #10

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    Quote Originally Posted by steve45 View Post
    Actually, checking for a thin coating of oil is the way to do it. Should be enough to lightly stain a brown paper bag.

    I'd still look for parts in the bottom, and coat all the bearings with oil if you're going to store it for a while. Of course, cover it with a plastic bag to keep dirt out.
    Awesome, thanks for the info. Based on that it sounds like it wasn't an oiling issue but the rings letting go.

    Brief history, the ski did sit for at least a year or two at my sister's in Havasu and when she went to start it for the first time since it sat the rings were seized. Spraying some penetrating oil into the cylinders, letting it sit, and with some coaxing we were able to free them up, it ran fine for 2 seasons. Wondering if maybe the rings broke earlier and it just took this long for the problem to show up (Rings slowly spinning around the piston until the broken part was exposed in the port and all hell broke loose?).

    Anyway, I guess it's not as bad as I thought it might be, thanks for the reassurance. I'll take some pics when I have a chance to dig in.

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