Check out this cylinder failure. 720
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  1. #1

    Check out this cylinder failure. 720

    What do you think caused this? Oil injection failure? Damage is only on the carb side.

    IMG_20200906_182250.jpg

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

    Lower rod bearing looks good, no discoloration. lack of oil for sure but maybe from water washing the cylinder down?
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  3. #3

    Re: Check out this cylinder failure. 720

    No evidence of water anywhere.

    Don't really understand what happened..

  4. #4
    Resident Guru SpitAndDirt's Avatar
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    Re: Check out this cylinder failure. 720

    I would remove the entire oil pump and RV cover assembly and test it for the proper number of drips using a drill. The oil pump may be good, but you could have a clogged/blocked oil injection check valve. On the 720, the oil pump has two check valves, one for each injection line, respectively. The check valves can be unbolted from the pump and cleaned using gumout and low pressure compressed air, but due to age, it might just be a better choice to replace both at the same time during your rebuild.

    https://osdparts.com/index.php?main_...oducts_id=4107

    This also assumes your internal carburetor micro fuel filters are clean and that the cylinder didn't turn out this way because of a lean running condition.
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  5. #5

    Re: Check out this cylinder failure. 720

    Quote Originally Posted by SpitAndDirt View Post
    I would remove the entire oil pump and RV cover assembly and test it for the proper number of drips using a drill. The oil pump may be good, but you could have a clogged/blocked oil injection check valve. On the 720, the oil pump has two check valves, one for each injection line, respectively. The check valves can be unbolted from the pump and cleaned using gumout and low pressure compressed air, but due to age, it might just be a better choice to replace both at the same time during your rebuild.

    https://osdparts.com/index.php?main_...oducts_id=4107

    This also assumes your internal carburetor micro fuel filters are clean and that the cylinder didn't turn out this way because of a lean running condition.
    Well.. Hrmm.. I have a single carb, that I sent out to a forum member to rebuild. I'd assume it was set up properly and not running lean.

    I'll inspect the lines and check valves. Thank you.

    -- Joe

  6. #6
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
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    Re: Check out this cylinder failure. 720

    Motor was tired & due to fail.

    Carb was rebuilt properly.

  7. #7
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    Re: Check out this cylinder failure. 720

    Let's see the exhaust side and piston top. Too lean will ALWAYS burn the exhaust side of the piston or piston top first.
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    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  8. #8

    Re: Check out this cylinder failure. 720

    I will have to take some more pictures tomorrow, but the exhaust side is perfectly fine.

    I was thinking about this earlier, you would think that the bearings would have failed before the piston did from lack of lubrication, no?

  9. #9
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
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    Re: Check out this cylinder failure. 720

    Piston will fail first from lack of lubrication.

  10. #10

    Re: Check out this cylinder failure. 720

    Quote Originally Posted by Grumpy Old Guy View Post
    Piston will fail first from lack of lubrication.
    That's my assumption, other cylinder is fine. I think I messed up when I disconnected the oil pump and didn't bleed it. maybe. I don't know.

    The engine only had 80 hours on it, which is why I put it in the boat (from a crashed ski). Compression was perfect before it blew up. I just want to make sure I resolve the lubrication issue.

    -- Joe

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