Replace Exhaust Riser?

[abelovarac]

Hello all!  I own a 1993 Mark 1.5 34 TR and have been reading about the need to replace the exhaust riser periodically due its tendency to fail at the most inopportune moment.  Since mine is 29 years old, and I have close to 2500 hours on the engine, I thought I'd have a look its condition.  After removing the insulation, I found what appears at first glance to be a solid riser with no visible leaks or cracks.  It's stainless steel with some rust around the elbow going into the manifold flange as well as the muffler, but as far as I can determine it seems pretty solid.  Not sure whether to go through the trouble of fabricating or buying a new one.  I am handy but don't have much experience with engines other than the usual maintenance.  Any thoughts from anyone who has more experience or a better eye for this?  Here's some pictures.  On the one showing the flange, note that I removed the top two nuts anticipating the possibility of replacement. The boat spent its first 18 years in salt water, but since then has been a sweet water boat on Lake Erie.

[Noah]

Doesn't look bad to me—a non-mechanic. I am guessing it has already been replaced previously. I don't think the original was SS—at least on the 25XP engines they were black iron I believe.

[Ron Hill]

Abe : Your exhaust riser looks pretty good to me.  I'd put the insulation back on it and then reinspect it in a couple of years again.  You have a very low number of engine hours for the age of the engine!! - which is why your riser appears in such good condition.  Always closely inspect the bends and welds of the riser!!

It looks to me that you have an M35 engine and the two top nuts that hold the riser to the exhaust manifold are missing! - or did you just remove them!?! 

Noah : FYI, The original C34s 1986 and into 1987 all had black pipe exhaust risers.  Catalina changed to stainless risers sometime during the 1987 production.

A few thoughts

[Noah]

Good info Ron. Thx!

[Stu Jackson]

I agree, looks pretty good.  Put those nuts back on the studs.  Before you start the engine.  Or you'll lose coolant.

Here are some tips for when you need to do this:

https://c34.org/muffler-exhaust-riser-replacement-2015/

[Ekutney]

Agree with other comments' looks in good condition.  I would suggest changing to the blue flexible hump hose, good way to reduce engine vibration transfer to the water lift muffler.

[abelovarac]

Thanks for all your input!  I wondered whether it had been replaced as well - looked pretty good for all those years.  Glad to hear 2500 hours is not that much - I didn't have any reference to judge.   I did take the nuts off the flange just to see if they came off easily and they did.  Won't forget to put 'em back on. I guess it goes along with that old saying - if it ain't broke, don't fix it.

[Stu Jackson]

Thanks for all your input!  I wondered whether it had been replaced as well - looked pretty good for all those years.  Glad to hear 2500 hours is not that much - I didn't have any reference to judge.   I did take the nuts off the flange just to see if they came off easily and they did.  Won't forget to put 'em back on. I guess it goes along with that old saying - if it ain't broke, don't fix it.

You're welcome.  All those years also is dependent on use and engine hours.  2500 is pretty good.  Dave Davis, a past Commodore, once tried to start recording failure times, but they were all over the place.  The top two nuts almost always come off easily, it's the bottom one that's a real bear.  My linked tech note article discusses that issue and MTBF on mine.  Good luck.

[Ron Hill]

Guys : Stu is correct, that bottom nut is a BEAR.  Just make sure that you soak it with Blaster/Penetrating oil and you use a 6 pt socket!!

A few thoughts

[KWKloeber]

Doesn't look bad to me—a non-mechanic.

The answer, of course, is to use the hammer test. 
Tap along the entire riser and at welds using a small-head ball peen hammer or a tack (upholstery, not sailing) hammer to sound for thin spots that may be near corroded-thru from the inside and not visible on the surface.  Not wailing on it, just tapping to sound it out (just like sounding out a hull or deck.)   Pay special attention to the condition of the injection wye which is typically the first to go.

[Sailing Sirona]

Wish I were in the same boat (so to speak)... I just recently started getting exhaust smell in the head and cabin, and investigated two days ago and found an exhaust leak where the raw water injection nipple meets the main body of the riser (and on the other end the threads of the rise at the exhaust flange are pretty rusted away)... looking like I'm going to have to replace the riser - so I've been reading all of the relevant posts over the last couple of days.  A couple of questions:

1) Any place other than Catalina or CD to buy the riser, or any point even spending much time looking? (I was talking to a Marine supply store near me on Vancouver Island, so asked, and they seemed to think there wasn't much option other than ordering from the US, from Catalina or CD)

2) Anyone had any luck with using automotive exhaust weld and/or tape as a temporary fix (i.e. until i can get a full replacement riser, flange, gasket, hump hose and do the full job)? --- kinda dreading the whole process.

[KWKloeber]

Steve

One option is to make up a heavier wall and longer-lasting riser using schedule 80 stainless pipe nipples and fittings.  Lower cost as well!

[Stu Jackson]

>>>>>>>>>>>>>>>>

1) Any place other than Catalina or CD to buy the riser, or any point even spending much time looking? (I was talking to a Marine supply store near me on Vancouver Island, so asked, and they seemed to think there wasn't much option other than ordering from the US, from Catalina or CD)

2) Anyone had any luck with using automotive exhaust weld and/or tape as a temporary fix (i.e. until i can get a full replacement riser, flange, gasket, hump hose and do the full job)? --- kinda dreading the whole process.

1)  Making up your own.  The Old Projects & FAQs (https://www.c34.org/faq-pages/faq.html) have some ideas:

https://www.c34.org/faq-pages/faq-exhaust-pipe.html

2)  The nipple is where they usually go bad.  Yes, muffler tape will tide you over.  From the 101 Topics:
Westerbeke Nipple Source  https://www.westerbeke.com/Product/NIPPLE/299693

[Ron Hill]

Steve : The nipple weld is usually the first thing that goes bad!!  I've written this up a number of times but here it goes again : 

The factory used wire reinforced hose to go from the anti syphon valve to that nipple. That stiff hose transmits all of the engine vibrations right to that nipple weld!!  Change that hose to a softer nylon reinforced hose.  I also recommend a stake weld on the inside of the riser to reinforce the outside weld.

If you haven't changed to a Hump hose (riser to muffler) now is the time to do it - That softer hose negates the engine vibrations to the fiberglass muffler inlet!!

A few thoughts

[ewengstrom]

This is what was left of our original riser.....obviously it had been bad for some time and I could tell there was an exhaust leak in the engine locker.
I measured carefully and ordered the stainless steel parts from a plumbing supplier and assembled it myself. (Ferguson Plumbing Supply)
Total cost was just over $100.00 in early 2020.
Luckily the nipple weld assembly was reusable,  it appears it was made from bronze or brass and is virtually perfect.