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  1. #1
    wes35's Avatar
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    Deep grooves under the rotary valve - 787

    My 1997 XP engine just broke for the first time after 13 years of happy ridding! I'm about to take it apart, looks like something broke loose (needle bearing?) and found its way into the rotary valve. The valve got bent the rotary shaft brass gear seems to be stripped down. The valve cover is damaged but that can be replaced or maybe machined. My concern is the damage under the valve on the surface of the crankcase, where can send it to get it professionally repaired? If I decide to rebuild it myself should I just sand it flat, replace the valve and the valve cover, and forget about the grooves being there?

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    Also if anyone know any local place to bore the cylinders or check the crankshaft in Chicago area please let me know.
    Last edited by wes35; 11-04-2010 at 07:47 AM.


  2. #2
    flyin' the friendly skies airbornexp's Avatar
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    my question is what caused it? needle bearing(s)? and have you found what was thrown?

  3. #3
    Nothin' better than Doo'in it! BigDaddyRXP's Avatar
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    IMO... your best bet is to have a reputable shop weld up the damaged areas, and machine it back to factory specs. I've seen way worse... and run just fine after a rebuild.

  4. #4
    wes35's Avatar
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    @Airbornexp, I'm not sure yet, I will take it apart over the weekend and I will post the findings and more photos. btw, I bought it brand new and never had any work done on it, it was still running strong until the moment it broke. (broke on landing behind a big wake)

    @BigDaddyRXP, any place you could recommend? I don't know any shops here so I'm willing to ship the engine case.
    Plus I just bought a cheap project boat (96xp) with similar kind of damage on the rotary surface so now I have two to repair (the second one is not as deep but going all around in a full circle!)

  5. #5
    Nothin' better than Doo'in it! BigDaddyRXP's Avatar
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    It appears that your in Chicago... there has to be plenty of capable machine shops around that area that can take care of that job for you! Just search around for a general machine shop... that's a "job shop" (takes in outside work), and go see what they can do for you.

  6. #6
    wes35's Avatar
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    The the piston chipped around the circlip to the point that the whole cirrclip got out, It made a deep "print" just below the pin and a smaller impression on the cylinder wall


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  7. #7
    Petron's Avatar
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    Quote Originally Posted by wes35 View Post
    The the piston chipped around the circlip to the point that the whole cirrclip got out, It made a deep "print" just below the pin and a smaller impression on the cylinder wall
    wow. did you notice any abnormal noises or lack of performance before all this happen?

  8. #8
    wes35's Avatar
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    No noise of any kind but an hour earlier it slightly felt like it wasn't accelerating the way it should, I checked the pump thinking that I sucked in some piece of plastic bag (#1 thing you get in your "prop" in Chicago) but couldn't see anything there

  9. #9
    "Tearing it up on the water" seadoobutch787's Avatar
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    I have seen the same thing on a 587. My buddy came to me with the scoring and grooves in the RV surface, the needle cage bearings came out and went through the engine.

  10. #10
    wes35's Avatar
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    Not a pretty sight, isn't it? The 587 has the caged needle bearings but the 787 are cage-less from factory and I decided to stay with them. Just ordered two sets from Parkeryamaha, they come in nice sleeve which makes them easy to install, removing is a different story as they tend to fall all over the place. Not fun especially if you doing top end only with the engine still in the hull, but the way I see it is worth the extra work, no cages to brake apart and for sure more contact surface for the heavy load from the piston/s
    BTW, cylinders just came back in freshly bored looking good. I'm rebuilding the motor just not sure if it will go back to the 97xp or maybe will go into a 96 I just got for $500!. looks like I will have some fun next spring as I also just bought a Factory spec2 pipe with ECWI and a set of Novi 42mm carbs! Planing to mill the head and maybe get the cyl ported.


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