Dreaded Cavitation issues 96 Speedster twin 717's
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  1. #1
    PWCToday Regular Kawi-doo94's Avatar
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    Dreaded Cavitation issues 96 Speedster twin 717's

    I have not been on in years until today since this speedster is getting the best of me!! Ive used the search button a million and one times with no similar issues to mine. So heres the story....

    Recently traded an item for said 96 speedster.. IT NEEDED A LOT OF WORK!!

    Im going to sum this up for sake of a long post.

    I have replaced the starboard motor with SBT reman. Also have replaced ALL of the carbon seals/orings/boots etc.
    Replaced wear rings and both impellers are Nujet impellers(that are new with no Knicks), although I'm unsure of the pitch. Both motors are now running great no issues and I have replaced all motor mounts and aligned.

    THE PROBLEM...
    I can get on plain great no problem but when each motor hits around 5k rpm they both seem to just let go and free rev to 7k/limiter.

    I have not tried putting rtv around the ride shoe yet because I don't think thats the issue BUT I can be wrong I'm just not sure.

    I have a new neoprene seal at each pump in between the housings and impellers.

    The weird part is that both motors are having the same issue! What an I missing gurus??

    Also when I come back down to idle and say "turn" and get back on it, it will start cavitation getting out of the hole.

    Im kind of a lost with it now...

    Also the rope protectors are cut off from both through hull fittings so those aren't the issue. Now the last thing.. My port side motors driveshaft is really rusty!! but not the starboard one. Could a rusty driveshaft really cause aeration leading to cavitation??

    Sorry for the long read!! Any help would be great!!

    Matt

  2. #2
    Resident Guru SpitAndDirt's Avatar
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    Which style of through-hull drive shaft seal are you using?

    Carbon ring or Grease-able aluminum block with shaft seals?

    Sent from my SM-N975U using Tapatalk
    "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed."

    -Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance

    Rides: 2 x 96XP // 99XPL // 02RX Currently rebuilding
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  3. #3
    PWCToday Regular Kawi-doo94's Avatar
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    The Carbon ring. I got the whole kit new from SBT.

  4. #4
    PWCToday Regular Kawi-doo94's Avatar
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    Im wondering if I should apply some rtv to the carbon ring where it attaches to the thru hull fitting. What do you think?

    Both thru hull fittings have new SBT carbon seal kits. so everything on the driveshafts are new besides the driveshafts themselves. Has anybody had success with just applying rtv to the exterior gaps of the ride shoes and plates?

  5. #5
    Resident Guru SpitAndDirt's Avatar
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    Pictures of your fittings?

    Some owners on here have complained that they never have had good luck with the carbon rings.

    The rubber bellows should definitely exert some pressure against the steel washer that it contacts. The steel washer should have 3 o-rings if I recall: two should be inside the steel washer(selling the gap between the driveshaft and the washer. The third is the fat o-ring which prevents the steel washer from sliding forward into the PTO.

    As along as all parts are in place, the carbon ring needs to ride as axially centered on the steel driveshaft washer as possible.

    Now here is the kicker: when running on the hose for testing, the carbon ring gets very hot. I dont remember ever seeing any info about supplying a spray of water to the carbon seal while testing in the shop manual(s), but it should be.

    I have found that the mating surface can become uneven and possibly even cause the carbon ring to crack.

    Whenever I run my 96 XP's on the hose, I have a garden water mister directly aimed at the carbon ring.

    While in the water, water is actually acting as a cooling lubricant between the two pieces while the driveshaft is rotating.

    It's a long winded explanation, but a misaligned carbon seal to driveshaft washer, damaged mating faces, or missing O-rings are all possible places for air ingress into the intake of the jetpump therefore possibly causing your cavitation issues.

    For some, upgrading to the newer greaseable style is a worthwhile modification.

    As for using RTV, you shouldn't have to as the hose clamps provide all the clamping pressure you need. Now, with that in mind, the hose clamps should be snug and not so tight that it deform the bellows or cracks the carbon ring.
    Last edited by SpitAndDirt; 02-06-2021 at 10:03 PM.
    "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed."

    -Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance

    Rides: 2 x 96XP // 99XPL // 02RX Currently rebuilding
    I love my CanDooPro! Take that stealerships!! www.candoopro.com

  6. #6
    PWCToday Regular Kawi-doo94's Avatar
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    Yes I got the three o rings with the fat one retaining the steel hat. With the new bellows its near impossible to compress the bellows. I had to wedge two 2X4's just to get them to slide back and slide the fat ring into position on the driveshaft to retain the steel hat.

    ill have to get a better picture in the am. but you might be able to zoom in enough to see them.

    IMG_0607.JPG

    Will those newer greasable fittings work on the driveshafts I have?

  7. #7
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    check to insure the thur hull fittings are sealed and no cracks.

  8. #8
    PWCToday Regular Kawi-doo94's Avatar
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    I’ll check that tomorrow and report back. I’m still just stumped that both motors/pumps do this at about the same rpm. Could a slightly bent driveshaft cause cavitation? Also on a side note they both had this issue with the old carbon seals and bellows. I’m wondering if I should just reseal the ride shoe and pump housing...

  9. #9
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    Did you align the drive shaft?

  10. #10
    PWCToday Regular Kawi-doo94's Avatar
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    Re: Dreaded Cavitation issues 96 Speedster twin 717's

    Yes both motors have been aligned and new motor mounts installed. Using the alignment tool from SBT.

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