Carbon Seal

[theinsider]

Have been reading a lot just trying to expand my knowledge on these 4-tec models before I potentially buy and came across someone saying that a "carbon seal failure" is very common and a design error that Sea Doo has. Any truth to this?

 

[devonte007]

The seadoo carbon seal is not a common problem nor is it a design issue. The type of drive shaft seal seadoo uses is now very common on most recreational boats that have straight shaft props. PSS Shaft Seal is a leading producer of these types of 'carbon seals' for boats and retrofit kits for the older style stuffing box systems. I personally think that seadoo was a leader when they came out with this type of seal back years ago after they switched from the carrier bearing type system.

The carbon seal may have gotten a bad rap because people do not understand how they work and that they can be ruined by running the boat out of water for prolonged periods or by the drive shaft being out of alignment. They rely on water to lubricate them and are designed to leak very minimally which is why seadoo does not recommend their crafts be stored in the water for prolonged periods of time (my boat stays in the water all summer and does not leak a drop).

Like anything they are not without maintenance. The seal relies on pressure from the corrugated rubber boot (commonly called the bellows) to maintain a proper seal. Over time the carbon seal does wear and becomes shorter and the rubber bellows loose their elasticity so the seal becomes weak and air can be sucked into the jet pump causing cavitation under hard acceleration. It may also start leaking water as it wears and gets older.

Overall I am a big fan of these carbon seal type drive shaft systems and think they work very well if properly taken care of. If purchasing a used boat you need to know what to look for and cavitation under hard acceleration is a key sign something is wrong and it could mean the carbon ring would need to be replaced among other things. Hope this helps some, if you have any more specific questions about this post back.

 

[theinsider]

Yeah I think you just about covered what I was looking for. I'm just trying to learn and it's easy to come across a rumor or theory and believe it as fact when I don't understand the terms they're using lol. I found out that the site I read this on was a heavy anti-SeaDoo website. Why they exist is beyond me, but I just wanted to know the truth.

 

[Coastiejoe]

They actually do a very good job and require almost no maintenance. Can they fail, yes. DO they fail, yes. But more often than not, they are VERY old when they do and or a motor mount or pump bearing has caused it.

 

[brobertov8]

Nice Thread!

Just one more question:

How to check if they are working well?
If I remove the sead, put the ski on the water and check if there is no any leak, should it working again? If no water leak, should it has no air leak to the pump?

 

[devonte007]

Just to clarify in my original post when I referred to 'maintenance' of the carbon seal I simply meant that it is a part that needs to be inspected periodically and replaced when it is worn out. Kind of like tires, not much you can really do to maintain them other than keep them inflated and replace them as necessary.

How to check if the drive shaft seal is working well? If you notice cavitation and have ruled out all other possibilities in the jet pump then there could be a problem with the seal. Some people have installed plastic zip ties onto the rubber bellows to increase pressure on the seal or even coated the mating surface between the stainless ring and the carbon seal with thick grease. After these attempts if the cavitation goes away temporarily, very likely you need to replace the carbon ring and bellows.

Air can leak through the seal under hard acceleration causing cavitation even though there is no water leak. The propulsion system is all about pressure, and it can create quite a vacuum on the drive shaft seal when in operation. While at rest there is no observable pressure so it may not leak.