Anatomy of a Exhaust Riser

Stu Jackson · Nov 21, 2012

dj2210 said:
It appears the leak was only at the threaded joint at the manifold flange.

Doug,

Nice work. When you put it back, what are you planning to use on the threads into the flange to avoid future leaks?

Yes, use the hump hose, save your muffler inlet port.

Anonymous 121765 · Nov 22, 2012

DJ,

A number of years ago I changed to a stainless steel threaded exhaust piping made up of fittings & nipples.

It worked well for about 3 years. I developed a leak at the cast carbon steel flange connector for the exhaust head.

The problem was s.s. vs carbon steel. The nipple ate away at the female threads in the flange because of dissimilar metals. I did some hunting and decided to go with a galvanized hard piped system & a replacement exhaust flange. It's going great for a number of years now. In addition, galv. is much cheaper to change out.

CR

jrowan · Nov 22, 2012

I agree with Capt. Ron. I have seen stainless steel fittings attached to standard or galvanized steel pipe plumbing fittings corrode at a much faster rate then they would if they were made of the same type of metal. The less noble ferrous or galvanized steel at the exhust flange will act as an annode absorbing corrosion from the di-electric corrosion cased by dissimilar metals. The salt water & air will accelerate the electrolysis effect. Sometimes sticking with cheaper is better in the long run for the sake of durability. I inspect houses for a living, & am continually surprised by how long some galvanized steel pipe lasts in domestic plumbing lines. It was designed to last for about 30 years, but I have seen it more then 60 + years old & not rusting away yet.

shipwreck66 · Nov 22, 2012

Old Skool Neil · Nov 23, 2012

FYI, galvanized pipe for use in the hot section is non-ABYC compliant and as the USCG has adopted the ABYC standard P-1 for exhaust systems, non-USCG compliant too.

Anonymous 121765 · Nov 23, 2012

DJ,

You,re right pal, I forgot to say anything about off-gasing of galv. pipe under heat.
I was told of this before I did my exhaust. The pipe will gas off the first 2 or 3 times it is heated. The gases are somewhat poisoness if you spend time below. So don't for the initial break-in process. After that, it is not a problem.

One suggestion for breaking-in can be done at the dock with the engine running in gear above 1800RPM for at least an hour. Next time, do the same thing. You will be able to smell the fumes at first. When the fumes stop, you're home free.

Don't forgrt the asbestos wrap.

It took 2 times for me to gas-off but I motored underway for an hour each way both out & back to my dock.

JR added a detailed explanation in his post that should answer additional questions about Galvanized pipe & dissimilar metals. He's OK in my book.

CR

Maine Sail · Nov 23, 2012

The ABYC specifies that all threaded pipe & fittings used in a marine exhaust system be made of Sched 80 pipe NOT the sched 40 I see most DIY's use. SS is very prone to fatigue cracking especially at the deep part of a thread due to the vibrations associated with engines.. It is also not technically "galvanically compatible" with the engine manifold, which is another ABYC requirement..

I simply use schedule 80 black pipe & fittings. It is relatively inexpensive and last just as long as galvy pipe. SS in sched 80 is going to be very expensive and more prone to failure....

Johnnie Walker Black · Nov 28, 2012

Uh... How hot does the exhaust get again?

Maine Sail · Nov 29, 2012

dj2210 said:
From searching the web for marine diesels somewhere between 300 F to 1000 F. When I put mine back together I would like to put a thermocouple under the insulation just to see.

Westerbeke/Universal & Hansen marine one of their largest master distributors use 400F Rectorseal...

I have not measured an aux diesel exhaust at over 375F and that was with a plugging exhaust elbow.. Remember the exhaust gasses are surrounded by a water jacket as they leave the engine and are only non-water cooled for a few inches...

catownersd9 · Nov 29, 2012

I have a 1984 Catalina 27' that has started leaking at the exhaust flange/manifold, the area is pretty rusted and probably needs to be replaced including the exhaust riser. I got a pretty pricey quote from the yard, said they would have to remove the engine to do the work. I have to imagine the work can be done without removing the engine entirely. What is the best way to access that part of the engine? Thanks for some guidance.

Anonymous 121765 · Nov 30, 2012

Guys,

Don't you think you're over-thinking this.
Boat diesels are small block retrofitted simple tractor diesel engines, Nothing more.

We're not building a watch, it's not NASA, it's a small boat engine.

There are more ways than one way to have a good exhaust system, but the concept & fix is much simpler than what this thread has grown into..............

CR

Maine Sail · Nov 30, 2012

captnron said:
Guys,

Don't you think you're over-thinking this.
Boat diesels are small block retrofitted simple tractor diesel engines, Nothing more.

We're not building a watch, it's not NASA, it's a small boat engine.

There are more ways than one way to have a good exhaust system, but the concept & fix is much simpler than what this thread has grown into..............

CR

Yep some schedule 80 black pipe, a proper injection elbow / point, some high temp exhaust wrap and some pipe dope....

Anatomy of a Exhaust Riser

.

Attachments

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.