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  1. #1

    Join Date
    Apr 2019
    Oklahoma City, OK

    Polaris MSX140 problem after top end rebuild

    I'm new to the forum but hoping to get some guidance. Have a 2003 MSX140 that I had to rebuilt the top end last summer. Had an oil injection problem that I didn't detect until it was too late and burnt up the cylinders to the point they had between 30 and 60 pounds compression.

    After fixing the oil injection problem and rebuilding the top end each cylinder showed between 120 to 130 pounds of compression. Initial test drive was short and it ran great. Second run was longer and again ran great. A few weeks later took it out and initially ran good but then after about 10 minutes started running rough and continued to get worse so took it back in.

    Tested compression and cylinders 1 & 2 were both over 120 pounds but cylinder 3 was at about 60 pounds compression. I have to assume the loss of compression is the cause of it running so rough but I'm not sure why I lost compression in that cylinder. Also even when I burnt up the motor it just didn't have power but didn't actually run as rough as it does now.

    I realize I have to tear it back down but wondering what I did wrong that caused the problem. I didn't touch the bottom end as it looked and felt fine as far as I could tell but possibly there is a problem there? Any thoughts and guidance would be appreciated. And I'm far from a skilled mechanic but normally good at working on engines and have rebuilt small boat engines in the years past that went off without a hitch.

    Thank you.

  2. #2
    Click avatar for tech links/info K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada

    After the first failure was there any metal debris (metal dust) in the engine bottom end?

    What did you do to fix the oil starvation problem?

    Are you aware of the need for all Polaris Ficht fuel pumps to have the internal pressure regulator reinforced?

    Lots more info here;

  3. #3
    martincom's Avatar
    Join Date
    May 2010
    Brainerd, MN
    As K447 alluded to, often these "meltdown" issues are attributable to a lean mixture which, in turn, is the result of low fuel pressure which, in another turn, is the result of the pressure regulator falling off inside the fuel tank. I believe K447 went through almost the same scenario as you with his former MSX140 where it melted a hole through a piston in minutes.

    See this thread for how to repair/reinforce the pressure regulator.

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