changing the driveshaft seal on an inboard ski boat

climbabout

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I have a 1997 Ski Centurion Elite Bowrider and I believe it's way overdue for a new driveshaft seal - it's never been changed. Rather than a slow steady drip, it now leaks constantly although slowly. I think it's been tightened as far as it can go. Any advice? Is this a do it yourself project? Boat is a straight inboard mercruiser/velvet drive combo.
Thanks
Tim
 

Ned L

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

Being a boat, it is a 'propeller shaft stuffing box'. Because you state "I think it's been tightened as far as it can go" I'm presuming it is a traditional stuffing box with packing in it and a hex packing nut and hex locking nut, and not a new 'dripless' type of stuffing box. It is and easy job, though getting to it can be less than ideal. If it has been tightened completely and still leaks ideally you would want to replace and not just add more packing, but often times you can just add a bit more. You need a couple of good size wrenches (pipe wrenches are usually ok), loosen the locknut and then back the packing nut completely off the shaft log (loosen it & slide it up toward the engine). If you are removing the old packing you will need a 'packing puller' (looks like a long flexible corkscrew) that you screw up inside the packing nut - you are actually screwing it into the old packing- to pull the old packing out. Once removed you cut (typically)three rings of new packing material that just wrap around the prop shaft and fit up inside the packing nut, stacked one after the other (three separate rings, not one piece that goes three times around). Then you tighten and adjust the packing nut & locknut & you are done. -- It should be adjusted with the boat in the water, better too loose than too tight. You want some wetness around the shaft and an occasional drip of water when under way. - If you are just adding some new packing you just back the nut off, add a ring or two of packing and tighten & adjust. You need to measure and get the right size packing. -It really is an easy job once you understand it.
 

climbabout

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

Thanks Ned - it is the OLD style and NOT a dripless unit. Sound pretty easy. Thanks.
Tim
 

Ned L

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

Good luck. It really is that easy. As I said, the most important thing is to not overtighten it. Worst case is if it doesn't get that little bit of moisture (water) to lubricate it and cool it the packing can overheat and sieze up. The result can be a scored prop shaft or worst case is the whole stuffing box siezes to the prop shaft and rips the piece of hose between the stuffing box and shaft log in half. then you have a bit of a problem. It is a good idea to give it a quick visual check for a while after you work on it.
 

climbabout

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

I'd like some of your expert opinions about the packing of the propeller shaft. Got the correct size packing from my local West Marine (3/16") and I was able to remove all the old packing - surprisingly there were only 2 rings installed at the factory. I also bought a small tube of packing lube/sealer made by the same company as the flax shaft packing that I bought. Package stated to coat the packing with a liberal amount and it would allow the shaft to run cooler and seal better - so I thought it would be a good idea. I cut 3 rings and coated them with the lube/sealer and moderately tightened the packing box. Well - I think it sealed the shaft a little too well - as soon as I put the boat in the water, I checked to see that I had the occasional drip from the packing box and to my surprise, I had to almost totally loosen the packing box to the point where it was only holding on with 1 thread - but as soon as I tightened the locknut to it, the drip stopped. So I ran at slow speed a short distance to see if the drip would start, and again I could not get it to drip, unless it was barely on. I ran for a few minutes at moderate speed - 2000-2200 rpm and rechecked - again no drip - but the shaft and packing box was not overheating at all - just barely warm to the touch. I ran maybe an hour total last night checking the shaft every 10-15 minutes and no overheating, but I'm still concerned that it does not drip.
I think the best course at this point it to remove the packing and clean all the lube/sealer out and reinstall fresh packing and forget the lube/sealer - the more I think about it the llube/sealer was a bad idea as the last thing your want is to have it sealed up with no drip. Am I on the right track here?
Thanks
Tim
 
Last edited:

haulnazz15

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

What about just removing one of the rings of packing? i.e. using 2 rings like you already had in it before the repair.
 

25thmustang

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

On my last boat, I redid the packing and it never dropped. It also never got about 85-90 degrees. New boat got new packing, it drips a bit, runs about 85-90 degrees.
 

Ned L

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

Oops, I forgot that on a small high speed inboard (like your skiboat) you may very well not get that drip of water when the boat is up on top and planing. The reason being that the water is going past the shaft log so fast that it sort of skims right past it and won't go up the shaft log. I think you'd see that you were to completely unscrew the packing nut and slide it up the shaft you'd have plenty of water coming in at idle and displacement speeds (below planing), and as you speed up the water will decrease to nothing at higher speeds. As long as I was getting that drip at slow speeds and the stuffing box is staying cool (or as 25thmustang says 80? - 90?) at high speeds I'd call it good. ---- Oh yes, that one thread issue. I also would probably take out a ring.
 

climbabout

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

Just a follow up - yesterday I removed the 3 rings of packing that I installed, cleaned all of the lube out from the packing box and the threads and reinstalled 2 new rings of packing(as the factory had done) with just a very light application of the lube being careful to clean the threads of any lube that might have gotten on them. Tightened the nut moderately and got a drip every 5-10 seconds at slow speed. Ran a couple hours at varying speeds and no problems!
Thanks
Tim
 

Ned L

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Re: changin the driveshaft seal on an inboard ski boat

Re: changin the driveshaft seal on an inboard ski boat

Good news! Glad it worked out fine.
 
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