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  1. #1
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    stimps 96 SLT780 rebuild thread <REDUX - 2nd ski>

    As noted in a different thread, I found ANOTHER 96 SLT780 and bought it.

    Found a 1996 SLT780, the EXACT same year and make as my recent purchase/rebuild, at the local dealer listed as a parts boat. Dealer said the PTO cylinder has lost some compression. Got it home and sure enough it has suffered edge erosion in the PTO. It looks like someone had the block halves apart and RTV'd them when they went back together. It is also around the rear seal. So first order of business will be taking the carbs off and disconnecting the exhaust so I can do a leak down test. She'll actually crank, but doesn't seem to want to stay running. CEN and MAG look OK, though MAG may be a bit lean. MFD doesn't power up, but I haven't checked the fuse yet and even if it failed like the last one I now know how to fix that most likely.

    Best part? $300 and it is really in better shape than my other 780.

    Here's a pic...


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    So I thought I would start a build thread here to detail the inspection and repairs.

    Getting started today I tore out the fuel pump and most of the gas lines, got the water rail off and then pulled the tops off the cylinders. I think I can see why the PTO had lower compression

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    So does this look like just lean damage or is there likely another problem with the PTO cylinder?



    The other cylinders look OK...though MAG looks a little lean to me.
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    Next steps will be pulling carbs off and rebuilding them, as well as the fuel pump of course. Gotta get the MFD out and dremel it apart to see what needs fixing in there. I will go ahead and tear the PTO bucket off, as it will as a minimum need to be bored/sleeved. What are my options there? Should I try to find a stock bucket and top (the top is all pitted from whatever got loose in there, looks like it was probably a piece of ring/piston).

    Do I need to take the whole engine apart to look for pieces?


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Split the cases and use the right sealant. Don't even waste your time trying to salvage someone elses F up!!!!


    That's my opinion.

    Great find BTW!!!

  3. #3
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Sort of tempted to just do a core swap with SBT rather than go through the whole engine myself, both from a competence and cost/time perspective.

    Would be a brand new engine in a great condition ski for $1k. But then I don't learn as much.

    Hmmmm...

  4. #4
    BlueFishCrisis's Avatar
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    Quote Originally Posted by stimpsonjcat View Post
    Sort of tempted to just do a core swap with SBT rather than go through the whole engine myself, both from a competence and cost/time perspective.

    Would be a brand new engine in a great condition ski for $1k. But then I don't learn as much.

    Hmmmm...
    Learn. My 2 pennies.

  5. #5
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Yeah OK, dove a little further into it. The PTO cylinder wall is pretty bad and obviously the piston is shot.

    So what is the order for removing things? I am stuck. I cannot get the one long bolt out of the top of the exhaust pipe, it hits the fiberglass edge of the ski before it comes loose. I also can't figure out how to get at the bolts that go thru the exhaust pipe into the exhaust manifold with the exhaust pipe on there. I got the three on the PTO out easily enough.

    Is there an alternative acceptable method of removing the piston pin or do I need to order the tool?

    I tried reading through the manual I got off Ebay, but I can't find a section dealing with order of removal of major components.

    I had a nut on the carb rail round off and ended up having to remove the carb rail and the intake manifold at the same time...those 10mm bolts are hard to get to!

    Oh the cylinders mic out to 2.802, is this stock? Manual says 71.3 which would be 2.807. There might be some carbon at the tops accounting for this.

  6. #6
    I'll be doing the same thing in 2 weeks to change out my CEN cylinder. I noticed the exhaust manifold bolt look very hard to get to. I already bought some wobble ratchet extensions and adapters thinking they would help, but it looks like the manfold bolts could be tough.

    It would be great if a couple of the experienced guys out there gave some hints to how this can be accomplished without pulling the engine.

    What exactly is causing you the problem of getting to the bolts? Would the right size wobble extensions help you?

  7. #7
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    OK, got the exhaust pipe off. I ended up just tweaking against the side of the ski from the exhaust pipe with a piece of wood to get the clearance I needed. Used a bolt and some ratchets to remove the piston pin.

    So now I am wondering if it might be worth it to get a stock piston and a replacement cylinder/head and gaskets and bolt it alll up and run a leak-down test. If it passes rock on and if it fails then tear the rest of the engine down.

    dswelch...I don't see how you would get the exhaust manifold off without removing the exhaust pipe. I did finally find a place where the manual gave this order...but there weren't any details on the...details.

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Sorry guys, not sure what it is you're asking?????

    As for the exh pipe bolts, I use a block to pry the hull, or something to spread the opening a bit to make the clearance needed. (not easy, but doable)

  9. #9
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Oh I also checked the timing today. I took a combination square and set it to 90 degrees. Ran it down enough to let the piston bump it near TDC. Then put a strip of paper around the shaft coupling.

    Place combo-square in PTO, rotate to contact in both directions, mark both locations. Repeat for CEN and MAG.

    Be sure to mark the place the paper overlaps! Mark that whole edge.

    Then remove the paper and re-align the overlap joint. Tape it shut.

    Now measure between each set of marks for each cylinder and mark the center of each set. Then measure the distance between each center mark. If they are all the same you are good to go.

    Pics...
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  10. #10
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Quote Originally Posted by xlint89 View Post
    As for the exh pipe bolts, I use a block to pry the hull, or something to spread the opening a bit to make the clearance needed. (not easy, but doable)
    DING!

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