Universal M25 Exhaust Riser Mixing Pipe

Sep 29, 2018
28
Catalina 30 Annapolis
I'm in the process of replacing the exhaust riser on my Universal M25 (Catalina 30). On the existing riser, there is a 90 elbow that is connected to a 1 5/8 inch OD straight 3 inch pipe threaded on the top only with the injection nipple on the side. The bottom of that pipe would connect to the hump hose / water muffler. I haven't been able to find that 3 inch pipe. Any ideas, or do I need to have one fabricated?

Thanks!
 
Feb 26, 2004
21,960
Catalina 34 224 Maple Bay, BC, Canada
Yes, below the nipple should be a straight pipe to go to the hump hose as you said. Ralph's right, 'cuz only those of us who know M25 engines would understand what you're talking about. It sounds like you've got a cobbled together niple/riser arrangement, rather than a prefab one, like Catalina or CD sell.
 
Feb 26, 2004
21,960
Catalina 34 224 Maple Bay, BC, Canada
I haven't been able to find that 3 inch pipe. Any ideas, or do I need to have one fabricated?
Also occrred to me: just take it into a hardware store and find the right length nipple that threads into the bottom of whatever that top piece is.
A nipple is just a straight piece of pipe with threads at both ends.
 
Sep 29, 2018
28
Catalina 30 Annapolis
Also occrred to me: just take it into a hardware store and find the right length nipple that threads into the bottom of whatever that top piece is.
A nipple is just a straight piece of pipe with threads at both ends.
Sorry, bad wording on my part. When I said nipple I was talking about the piece at a 45 degree angle off the side that is welded to the straight pipe that the raw water is injected through.
 
Feb 26, 2004
21,960
Catalina 34 224 Maple Bay, BC, Canada
OK, what you show is pretty much what I figured out on my own of what you have, which appears to be a cobbled together exhaust riser made from individual pieces of either black steel or galvanized pipe. It appears to be home made, rather than a purchased piece from C or CD. But mebbe not, I'm not there to check the material.

What you bought from Westerbeke is a pretty good find on your part, not many folks know about it.

What your real challenge is that you have the old entire assembly which was built to match the physical constrains of the space between the back of your exhaust manifold and the inlet of your muffler. And what you bought does not fit into that geometry at all, because it is not an exact replacement for any individual part or piece of what you have removed for replacement.

Your old assembly has the inlet nipple on the TOP of the horizontal part of the assembly. The new WB piece will have it on the vertical piece.

Because you are the ONLY person in the entire world who is anywhere near being on your boat, you will have to figure out the geometry of any and all additional pieces that need to be added to the new WB piece to make it fit and connect the manifold and the muffler.

For credibility's sake, I, too, have an M25 and have replaced three risers, so I know.

The other option is to return the WB piece or sell it, and ONLY IF you have a standard C30 PHYSICAL arrangement between your engine and the muffler, buy one from Catalina Direct. Exhaust System

They seem to have four different ones, so no matter what you do, you're in for some serious measuring.

Good luck.
 
Sep 29, 2018
28
Catalina 30 Annapolis
Stu,

Thanks for your reply. Perhaps I'm not understanding, and I'm guessing it doesn't make a difference, but I believe the inlet nipple on the the old riser runs vertically as well. I didn't measure down from the top of the old and new pipes to the inlet nipple, but the new one is 3 inches longer overall. I thought that by going the sch 80 black pipe route I'd be able to customize the fit and might be able to avoid a potential issue with the CD prefab riser not fitting exactly. This winter, i pulled my engine, had trans rebuilt and put it back in last night. I will likely have the yard do the alignment and wonder if all of that might affect the riser measurements at all.
 
Feb 26, 2004
21,960
Catalina 34 224 Maple Bay, BC, Canada
I will likely have the yard do the alignment and wonder if all of that might affect the riser measurements at all.
That should be taken up by the use of the hump hose. The end of the riser at the muffler end then becomes a non-critical but important piece of the puzzle.
but the new one is 3 inches longer overall.
You're the ONLY person who is there. I simply don't know if it will fit.