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    Mattia1988's Avatar
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    Apr 2019
    Miami, FL

    Sudden knocking at low rpm on 1998 Polaris SLTH & loose drive shaft/thru bearing

    Hi everyone, so this weekend I took my ski out for a ride in very choppy (ocean) waters, we were 2 of us on it and I kinda pushed it to the limit at times, maybe a bit too much - especially because the ski was constantly jumping off the waves and running high on rpm. After approx. 3 hrs, I slowed down and started feeling a mid to semi-heavy knocking at low rpm, which would disappear if I gave it mid or full throttle, only to come back right away once I slowed down to low or idle rpm conditions. At a certain point while on idle, it even turned off like the engine and/or the shaft got stuck , but re-started immediately once it was turned on again.

    I had the instinctive impression it was the drive shaft going out of alignment, knocking all around and causing pretty definitive vibrations we could feel or at least hear through the hull. We made our way back to the ramp at mid throttle just to stay on plane and be quick, w/o pushing it too much as I wasn't sure the engine was also involved.

    First thing I did once it was on the trailer was to open the seat, and noticed almost immediately that the metal clamp of the plastic protector around the drive shaft was totally loose (almost detached from the shaft coupling guard), then I started it to see if anything would look unusual, and noticed the drive shaft would turn visibly loose (1-2 mm), along with the black bearing housing & the coupling guard - see below photos.

    Can anybody give me a hint on whether that might be the issue? I have videos but apparently those cannot be uploaded here. I had no water inside after a full 4 hrs out other than the usual one on the bottom that flushes away in 3-4 secs after I remove the drain plugs, but that never reaches the bilge pump proximity so it just seats there while I ride w/o being expelled.

    I will also check cyl compression and all that to make sure the engine is firing well and pistons/rings/cylinders are healthy, but wanted some opinion first - the drive shaft is loose from the inside if I grab it, wobbling a mm or 2, while the part under the hull that connects to the water pump (sleeve) appears firm when I grab it.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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