Exhaust Bellows vs. Tube

[Sunking22]

I've been reading about doing my own bellows replacement here and it sounds very doable. I also hear lots of folks recommending using an exhaust tube vs. putting on a new bellows. Well my boat is an 86' Wellcraft with a 4.3L mercruiser and alpha one and the previous owner put a tube on it which is why there is always this nasty exhaust grime all over the bottom of the buillt in swim platform and around the outdrive area. It took me forever to figure out why it was there and other similar built boats didn't seem to have this issue, then another boater pointed out the tube. Since it doesn't connect to the outdrive there is constant exhaust fumage boiling up in that area and creating the nasty film on the boat. And for anyone who wants to say that it only leaks when the outdrive is up - they can come wash my boat every Monday. So the morale is - if you don't mind scrubbing exhaust grime from the rear area of your boat all the time then the tube will save you some time at replacement - if you want it right use the bellows. Just my 2c.

 

[zbnutcase]

Re: Exhaust Bellows vs. Tube

Agreed. The tube is the lazy man's way out.

 

[45Auto]

Re: Exhaust Bellows vs. Tube

Good point. The bellows will send it all through the prop and keep it from bubbling up directly under your transom when you're not on plane. However, if you're running a big block and using the prop exhaust, Mercruiser recommends using a tube. At higher RPMs the volume of exhaust flow from a big block will be restricted by the exaust passages in the drive.

From the Mercruiser Gasoline Installation Manual, 90-863021020, May 2002, page 41 (496 HO, 425 HP):

MAGNUM BRAVO MODEL EXHAUST RECOMMENDATION

Note: If noise regulations do not allow the use of through the transom exhaust, an exhaust pipe kit (Quicksilver P/N 44266A6) must be installed for the through the prop exhaust. This kit also contains an exhaust tube that is used in place of the exhaust bellows.

A lot might also depend on the type of motor and how clean it runs. A computerized fuel injected motor will generally run leaner and cleaner than a carbed motor. My fuel injected motor came with a factory tube, it's 7 years old and I've never noticed any grime or film under the swim platform. It's also still running on the original spark plugs that still look brand new, which is a good indication of how clean it's running.

 

[Brentathon]

Re: Exhaust Bellows vs. Tube

There was a service bulletin that said to use the tubes on big engines, because the corregated bellows style could expand under pressure, and press the U-joint belows into the U-joint. Probably not likely.

There are 2 other exhaust port holes in your transom assembly that allow any "excess" exhaust that doesn't go through prop hub to exit these 2 holes. When not in gear, MOST of the exhaust exits these 2 ports, rather than the prop hub, as the prop hub is much lower in the water column.

I like the corregated bellows, at it is quieter. Either bellows allows for the exhaust to exit via prop hub, there's a natural low-pressure that draws exhaust through prop hub.

 

[FreeBeeTony]

Re: Exhaust Bellows vs. Tube

I have the tube..........no grime here.

Maybe your engine isn't tuned properly.......

 

[rbh]

Re: Exhaust Bellows vs. Tube

http://forums.iboats.com/showthread.php?t=410985

#6 post has the mercruiser write up.

 

[Bondo]

Re: Exhaust Bellows vs. Tube

and the previous owner put a tube on it which is why there is always this nasty exhaust grime all over the bottom of the buillt in swim platform and around the outdrive area. It took me forever to figure out why it was there and other similar built boats didn't seem to have this issue, then another boater pointed out the tube. Since it doesn't connect to the outdrive there is constant exhaust fumage boiling up in that area and creating the nasty film on the boat. And for anyone who wants to say that it only leaks when the outdrive is up - they can come wash my boat every Monday.

Ayuh,... Fix the carb so it ain't runnin' so Rich,+ you won't have a soot problem...
It's got Nothing to do with the tube, vs. bellows...

 

[jtmarten]

Re: Exhaust Bellows vs. Tube

Agreed, sounds like you're running rich. I've run the tube on previous boats and never had any grime/soot/etc collecting around the transom.

 

[Captain Ben]

Re: Exhaust Bellows vs. Tube

Are you planning on doing the other bellows or gimbal bearing while you are in there?

I am replacing my shift cable bellows, and don't know what other ones to buy.. but i don't want to do this again next year.

 

[Sunking22]

Re: Exhaust Bellows vs. Tube

Well after reading all the great feedback here, and then spending time on the quardrajet threads, I'm going to attempt to adjust my carb this weekend and see if I can get rid of the gunk - which would be fantastic. To answer Captain Bens question - If adjusting the carb doesn't seem to work then when the time comes for a full bellows job I'll put it on. Right now I'm not getting any water in my bilge (knocks on wood) and I'm a big fan of "If it ain't broke don't fix it."