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  1. #1
    Mattia1988's Avatar
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    Sudden knocking at low rpm on 1998 Polaris SLTH & loose drive shaft/thru bearing

    I am re-posting under the right Forum (sorry for the duplicate!).

    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.
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  2. #2

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    Hi, I don’t fully understand. Is there play in the shaft but not the engine coupler, or does the engine coupler move too? If the engine coupler has play you have bad crank bearings, if only the pump shaft has play you probably have bad jet pump bearings. If the shaft has play inside the coupler there is something wrong with the coupler.

    Either bad crank bearings or bad pump bearings can cause a knock and bind up, killing the motor as you described.

  3. #3
    Mattia1988's Avatar
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    There's a play when I grab the black bearing housing & sleeve that are attached to the "thru-hull" section of the shaft. The housing is also attached to the coupling guard (the black plastic-rigid protector that covers the section of the shaft connected to the engine, whose clamp was almost detached).

    I notice no movement from the shaft in the part that connects to the engine block, it looks like there's play inside the bearing housing (worn bearings?) that, my feeling is, causes the impeller to go out of alignment and "colliding" with the pump housing, or get stuck due to the play.

    Would this make sense or am I potentially missing other causes I need to rule out first?

    Is the bearing housing + bearings replacement something doable w/o engine alignment and other special tools? What's the easiest way to replace them?

    I guess the jet pump has to be taken out, but does the pump plate (with all the sealing glue) has to be taken out too?

    I'll check the usual signature links w/all info but if you can give me an initial input it'll help a lot, thanks for your reply btw.

  4. #4

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    Pull the pump by disconnecting steering and reverse linkage at the back, then the four long bolts, careful, they break easily. The nozzle will come off easily but the pump may not. K447 has instructions posted as to how to remove it. The bearings are in that part.

    At this point there is no need for alignment providing it was good before. Now look inside the housing that is still bolted and sealed to the hull. Did it get badly chewed up when the bearings failed? If you need to remove that, alignment will be necessary. I’ve also been told that is very difficult to remove because of all the sealant. You will also want to check the impeller to see if it is badly damaged.

    I only have experience with a Genesis. I’m assuming yours is similar but if not I apologize for anything I posted that may be misleading. I’m not sure if some of these skis have a replaceable wear ring or not.

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  6. #5
    Mattia1988's Avatar
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    Thanks for your input! I will check his signature links, they are very detailed but it's easy to get lost at the beginning through all that info (being w/o much experience on skis), and with this intro you gave me it should be easier to start.

    Just to confirm in your second paragraph, when you say "now look inside the housing..." after the nozzle and pump are taken off, do you mean from the rear through the thru-hull whole? In that case, I would be looking at the bearing housing from the inside, am I right?

    Is the plastic sleeve with the 2 clamps the part that is difficult to remove, and that requires re-alignment if removed? Because that is exactly the part that shows a play in my ski.

    Also, the drive shaft has a slight longitudinal play when I turn the engine on, meaning it plays a few mm towards the engine and then back towards the pump (but not towards the walls of the hull, laterally).

  7. #6

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    Yes, look in from the rear, at the inside of the pump shoe, (part that is sealed to the back of the hull on the outside). This is the part that, if removed, will affect alignment and is the part in which the impeller spins. Hopefully it is not badly damaged. I guess at this point you would be looking at the inside of the through hull bearing and seal assembly but no, it is not the part that is hard to remove, nor does it affect alignment.

    To clarify, you did say earlier that there is lateral play in the shaft which shows up in the through hull assembly, correct? I believe a small amount of longitudinal play is normal but I wouldn’t consider it normal to see the shaft continuously working back and forth.

    Also, I’m not sure if you’re clear on this, the through hull assembly you are describing as a plastic sleeve plays no part in stabilizing the shaft, only sealing it. If there is play in the shaft it is because of bearings further out in the pump.

  8. #7
    Mattia1988's Avatar
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    Thanks a lot for your input, so I pulled out the jet pump and found out that the bearings in the pump were long gone, almost locked (can't even spin the impeller by hand). Got a used pump with good bearings and nice impeller within specs for $120 so I put that on, together with brand new thru-hull bearings (those were also worn out and were allowing some water in. I bought the newer part in aluminium that does not support the plastic coupling guard) and a used but good drive shaft (which was slightly worn too!). Don't even see a single drop of water coming in when out on the waves. Spent $220 total, which isn't that bad at all since the ski is running better than before. I am rebuilding the other pump but I guess I'd need some tool to take out the bearings and put in the new ones. The impeller is torqued at 100ftlbs which feels like melted into it. Also, the impeller blade edges were badly worn due to misalignment created by the faulty bearings in the pump, which messed up everything in between the engine and the pump. I didn't take out the pump "shoe" though so I didn't need engine realignment. All this because the 79 cent o-ring of the pump cone went bad and allowed salty water in, creating all this mess in a matter of minutes. Now, I see there is an o-ring there BUT the manual also lists a gasket that goes in between the cone and the pump, not inside where the o-ring goes but on the perimeter where the cone attaches. Couldn't find it anywhere so I applied a very small amount of marine silicone to ensure the cone is 100% waterproof sealed. The O-ring on drive shaft was still good, felt strong suction when pulling the shaft out of the pump and it's still shiny black. The back n forth effect on the previous shaft was due to one of the black "caps" on it that fell, I found it inside the hull. The 4 ling bolts are a pain as they feel like they can break at any time, used all possible precautions like DW40 and other products before touching them and torqued them slowly to specs. Cleaned all parts from salt and corrosion before reassembling. Any suggestion on how to do maintenance on these parts?


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