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  1. #11

    Re: Check out this cylinder failure. 720

    So. I checked the oil lines, and they have oil in them, the squirter appears to have oil. So now I'm not sure that it's lubrication after all.

    The other piston has absolutely no signs of any damage or issues.

    Here is some pictures of the exhaust side of this piston - as you can see there is SOME damage, but it's quite minimal compared to the RV side.

    Also the piston top, the cylinder, and the plugs.

    Sleeve might have had a crack in it, or maybe it was a crack from pounding it out. Sending the cylinder next door tomorrow to get bored and honed to size. I don't want to put this back together until I know for certain why it blew up.

    -- JoeIMG_20200909_161006.jpgIMG_20200909_161001.jpgIMG_20200909_162101.jpgIMG_20200909_161554_2.jpg

  2. #12
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
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    Re: Check out this cylinder failure. 720

    You need to bore both cyls the same.

    You should have bled the oil pump a air pocket in the oil pump will cause what you have.With that said I would also premix the next tank of gas after you drain it completly & start with fresh fuel. I do that carb mod/rebuild to a ton of skis/jetboats & have no issues whatsoever. If you wanna send it back I will be happy to check it out no charge.

  3. #13

    Re: Check out this cylinder failure. 720

    Quote Originally Posted by Grumpy Old Guy View Post
    You need to bore both cyls the same.

    You should have bled the oil pump a air pocket in the oil pump will cause what you have.With that said I would also premix the next tank of gas after you drain it completly & start with fresh fuel. I do that carb mod/rebuild to a ton of skis/jetboats & have no issues whatsoever. If you wanna send it back I will be happy to check it out no charge.
    I don't think there is any issues with the carb.. I'd expect both cylinders to be lean.

    One thing I cannot explain though, when I first got this on the water it kept dying after like 45 seconds to a minute of throttle. It would immediately restart. It did this over and over and over again. I drained all the fuel, new fuel, bypassed the shutoff valve and ran new lines to the reserve side of the sender and tried it on the water again and it did this over and over again.

    The ONLY thing I did after that was change the short tubing for the fuel pulse line. Went back on the lake, and it ran perfect. ran it headway speed for about 10 minutes, then brought it up on plain and ran about 3/4 throttle for another 5 or so minutes and it just died. Never started again.

    Anyhow, I put a new sleeve in the cylinder and I'm having the machine shop bore it to factory specs to match the other cylinder on the final hone.

    So you think that an air bubble from when I disconnected the line to the squirter for that cylinder caused this? Or perhaps an air buble in the main line? I had the main oil feed line disconnected of course, the motor was sitting on my bench for a year or so before I put it in the boat.

    I spoke to one of the techs at the Seadoo dealer down the street, and showed him the pictures. He doesn't think it was a lubrication issue, but rather he thinks the crank seal for that cylinder failed and it was a lean condition. While I do see a minor difference in the plug, It doesn't look like it was that lean. Does it?

    I don't do much with the 2 strokes. I built a ton of 4 stroke engines. I got out of this seadoo stuff for a lot of years and got back into it recently. Starting to regret it haha.

    -- Joe

  4. #14

    Re: Check out this cylinder failure. 720

    Started the re-assembly with new parts. So I'm going to put the top end together, and I'm making some block off plates for the carb and exhaust. My plan is to pressurize and then vacuum test the crankcase to check the crank seals for air leaks. If that checks out, I guess we have to assume it was a lubrication failure.

    I'll also drill / drip test the oil pump.

    Then I guess we'll see how it goes with a full tank of premix.

    -- Joe

  5. #15

    Re: Check out this cylinder failure. 720

    Top end is back together. I need to make a block off plate for the carb and exhaust so I can do a pressure / vac test of the crank case.

    Looks like I have to remove the entire RV cover then separate the intake from it to test the injection pump??

    -- Joe

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