Mid 80's Alpha One Gen One Transom: Exhaust Tube or Exhaust Bellows?

[San_Diego_SeaRay]

Quote from pg 4B-6 of Mercruiser Svc Manual says the following:

Exhaust Tube Use on V-8 Drive Shaft​

Extension Models​

Early MerCruiser IR-IMR V-8 Drive Shaft Extension​

models were equipped with an exhaust bellows.​

Later V-8 drive shaft extension models utilize an​

exhaust tube. If servicing a unit equipped with an​

exhaust bellows, bellows should be replaced with a​

tube, as excessive exhaust gas back pressure will​

result if bellows are used. In addition to affecting​

performance, excessive pressure may cause​

exhaust bellows to balloon out and contact U-joint​

bellows, pushing them against U-joints. Eventually,​

the U-joint bellows may chafe through with a​

subsequent water leak resulting.
​

But you can still buy exhaust bellows for these transom assemblies, and they seem to be quite common. What gives? Should I insist on replacing my exhaust bellows with an exhaust tube?

(My engines are 1982 MCM 260s but the transom assemblies are from the mid 80s)

 

[Bondo]

Drive Shaft Extension Models

Ayuh,..... How far forward are yer motors mounted,..??

That's for the drive shaft extension models,.....

 

[alldodge]

I don't see this being a big issue, but depends on how you use your boat IMO. If your the type which runs a lot of close to WOT, then yes you need a tube, otherwise not necessarily. Other wise, a tube with a V8 and Alpha drive will allow the engine to breath easier. It will increase exhaust noise a bit. If it was mine, I would use the tube just because there easier to install and the engine has an easier time, but may not really be necessary.

 

[San_Diego_SeaRay]

Ayuh,..... How far forward are yer motors mounted,..??

That's for the drive shaft extension models,.....

Good point. Reading that again, it does seem pretty clear that this is for those models. My motors are mounted just a few inches from the transom plate; so probably not a drive shaft extension model? Seems strange that this would make a difference in how much exhaust pressure is created....

I don't see this being a big issue, but depends on how you use your boat IMO. If your the type which runs a lot of close to WOT, then yes you need a tube, otherwise not necessarily. Other wise, a tube with a V8 and Alpha drive will allow the engine to breath easier. It will increase exhaust noise a bit. If it was mine, I would use the tube just because there easier to install and the engine has an easier time, but may not really be necessary.

Well that helps me understand my options but I had already bought the bellows version so lacking a clear need for it, I'll just stick to the version I've purchased.