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  1. #1
    dcuhpw's Avatar
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    Putting threads on jet pump shaft 15f

    Thinking about threading the shaft on my 2010 15f jet pump to add a nut on the back side to prevent the shaft from moving forward if a bearing fails. Impros does this service for the ultras but I see no mention of it for the stx.
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  2. #2
    dcuhpw's Avatar
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    Another possibility I was thinking of is putting on a press fit colar in that area to provide a better hold. The thrust from the pump is somewhere in the 900lb range so a press fit of 1100 or more lbs should be plenty strong also

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    I'm not following. I think you are saying thread the pump shaft by the two flats on it used to remove the pump shaft. If this is the case, I don't see what it buys you. The pump shaft is threaded into the prop. The prop can only slide back so back based on the splines on the drive shaft. I'm guessing that won't be to far.


  4. #4
    yes do it and add the exstra bearings to the front

  5. #5

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    Cato3,
    Reason for this if there is a bearing failure the shaft walks forward and ruins the engine. Double vane set ups have this set up I think after 2013 or something. The nut on the back of the shaft will prevent this.

  6. #6
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    Ok I see the double bearing on a 2014 pump shaft. I can see how that will give the added support to the pump shaft but I'm nut understanding the nut modification. I have two 2005 STX-12Fs that are stock, so I would like to understand this modification.

    I'm sorry guys but the old saying is a picture is worth 1000 words. Thanks!!

  7. #7
    dcuhpw's Avatar
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    Quote Originally Posted by cato3 View Post
    Ok I see the double bearing on a 2014 pump shaft. I can see how that will give the added support to the pump shaft but I'm nut understanding the nut modification. I have two 2005 STX-12Fs that are stock, so I would like to understand this modification.

    I'm sorry guys but the old saying is a picture is worth 1000 words. Thanks!!
    The whole issue is the rear bearing. If rear bearing fails, the impeller shaft will allow the impeller to slide back towards the engine. Essentially the thrust from the impeller at the end of the driveshaft shoves the driveshaft straight into the engine and can wipe out your thrust bearing and destroy your engine. If kawi would simply have done some more machining on the housing and rethought the bearing layout this would be a non-issue. The nut sits in the nose cone at the end of the shaft (towards the rear of the ski) and acts as an extra safety. A failure at the front pump bearing can be bad and destroy your liner and impeller but the thrust from the impeller will destroy engine internals if the shaft slides forward and the double bearing setup does not prevent that. Impros does the mod to the impeller shaft for their 250/260 pump modifications. Personally, I went with the kawi performance kit since I needed a few replacement pump parts anyways so o just got the kit which includes everything. Green loctite at the rear inner bearing race may also be helpful. Either way, frequent pump inspection is critical

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  9. #8
    ps and make sure you locktight the impeller too or a bunch of bad stuff will happen ow make sure your impeller to wear ring is 2-8 thousands service limit is 20 thousands this helps a lot with cavitation .

  10. #9

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    I take my pump apart 2 times a year since my issue. The problem is shaft seals let water into the housing and gets water in the bearing and then it makes a mess. I have a complete re-build and re-welding the edges of my impeller on here somewhere. The liner was pretty easy to do. My pump to liner dimension is right at .006". I got this close as I welded up the impeller ends and machined it back down to that clearance.

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  12. #10
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    Quote Originally Posted by Waveraider12 View Post
    ps and make sure you locktight the impeller too or a bunch of bad stuff will happen ow make sure your impeller to wear ring is 2-8 thousands service limit is 20 thousands this helps a lot with cavitation .
    I NEVER use Loctite on the impeller shaft. I use marine grade anti-seize and torque properly. Most factory service manuals recommend anti-seize also. Threadlocker may help seal out the threads a bit.

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