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  1. #1

    657 lost compression in rear cylinder. Your thoughts please.

    Back story:
    Bought two waverunners (02 XLT 1200(blown cylinder) + 94 GTX 657.

    I wanted the double trailer and the yama but the doo was in PERFECT condition had 155psi in both holes so I sold the Yamaha, and prepped the Seadoo for it's first ride.

    On the water my wife was riding and after about 20-30 minutes it started to sputter and then lost power. She limped it back to the shore. It barely would start and would not go more than 5 mph.

    I took it home and ran a compression test. Still solid. So I figured I had a carb issue and I had no history of the carbs. I installed two Genuine Mikuni kits and new 2.0 needle/seats. Hi/low speed adjusters were setup according to spec. I went ahead and converted to premix and went about 36:1. I had also completely removed the tank, cleaned it and reinstalled with a fresh filter.

    Within a few cranks she fired to life and sounded great! Took her to the lake last Sunday and when she hit the power. I brought it up on the sand...revved it out...and back in the water she was PERFECT! After about 20 mins of wife brought it in so we could switch. She said it shut off on her once and hesitated(I know now it was seizing). It never started again once she shut it down.

    Back home it had 85psi in the back and still 155 in the front. It would still fire up but not good obviously. Last night I pulled the aft piston/cylinder and what I found was pretty wild. First off...NO DAMN TOP RING! LOL. It's an old SBT motor(March 2011 according to them). Even more wild is there is no damage from the ring ever coming apart. The bottom ring was stuck on the exhaust side and there was evidence of the piston getting really hot/melting a little. Anyway...the bore is actually not that bad and remember it had 85psi with a stuck ring.

    Two things. We only have one more trip on the water this year so I'm thinking about a quick hone and rering and get it back on the water. Over the winter I'll go through the entire engine. But I obviously have a lean condition out back. I'm thinking crank seal or carb obviously but the carbs are fresh and I have built more damn Mikuni carbs than I care to think about.

    But alas...I came here for your opinion so please share.



    P.S. Pics tonight!

  2. #2

    Join Date
    Mar 2006
    if it ran GREAT before you touched it, I would suspect what was just touched-- the carbs. I would order 2 pistons the next size over, bearings and gaskets and just do it right, but if you are not confident in your carb work, get a fresh set of eyes on them to check your work. 2.0s for instance? What did your carbs come with stock and why did you change them from the GREAT running setup? New filter, lines, routing of the lines, selector switch-- ANYTHING you touched...

  3. #3
    If you're positive that there was no upper ring on that piston and you can't find any signs of it in the bottom of the case, I would be tempted to do just that, hone the cylinder and install 2 new rings (up & low) and see what you get.

    I understand why you think you're lean on the rear cylinder, but I wouldn't make that call until it's set up right with both rings installed.

  4. #4
    Jim - it has been run twice and both for 20 minutes before it died
    1. still on oil pump. carbs not touched. Lost power but came back
    2. carbs on premix and rebuilt to factory specs. Lost power after 20 mins and never came back

    the carbs called for 2.0 seats. I just replaced everything with original equipment. Pics soon...
    Last edited by vdubspeed; 08-07-2014 at 08:18 PM.

  5. #5
    Okay...pulled the motor. Everything looks like...well a used salty motor. LOL. Went ahead and freed the stuck ring and for laughs and giggles...tossed that cylinder back together and got 120psi. That's a 35psi increase JUST by freeing the stuck ring and the doctor is still out on the missing top ring!!!'s the worst damage. I'm SERIOUSLY considering tossing a quick hone and some rings on it and rechecking the compression. Then I plan to back the high speed adjuster on the back carb or maybe go up one main so this ole girl gets some more fuel.

    I figure a set of rings is 27 bucks so if I can get the compression's worth a shot.


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  6. #6
    blairwill4's Avatar
    Join Date
    Apr 2014
    Fort Wayne IN
    That wash is super lean on that cylinder. Depends on if youre willing to have a blown up motor? you might get some time out of it but piston rings dont just dissapear. Id be afraid it fell down into the crank and might be about to cause havoc.

  7. #7
    Quote Originally Posted by blairwill4 View Post
    That wash is super lean on that cylinder. Depends on if youre willing to have a blown up motor? you might get some time out of it but piston rings dont just dissapear. Id be afraid it fell down into the crank and might be about to cause havoc.
    Yeah the only thing I can think of.'s gone three years with that jetting. Group K has bowed down and said rear cylinders like a little more fuel or less time so I plan to go up one main in the back. I suspect an air leak to be honest. I'm going to do a leak test on the motor when it's back together.

    The top ring deffo not in the crank area. Furthermore... look at the signs of getting an ENTIRE ring broken apart and washed away. I've seen plenty of pistons after a ring frags and some of the pistons will actually keep some of the ring! LOL

  8. #8

    Join Date
    Mar 2006
    That is not an oem piston, so that motor has been apart atleast 1 time. It may be that the last builder/hack mechanic did not install the top ring. EVERYTHING is now suspect.

  9. #9
    Myself's Avatar
    Join Date
    May 2007
    North Central Arkansas
    That motor is a piece of cake. Go ahead and tear it down, clean and beadblast everything, then re-assemble with new crank seals,rings, pistons and bore if needed, and some fresh paint.

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