Tech Wiki

Exhaust Pipe Replacement

I was looking into replacing the exhaust pipe for our boat. I contacted Catalina direct and got the part number, price etc. from them. To my surprise they told me that their part did not include a flange fitting to mount to the engine manifold and that I would have to purchase the part from "Trans Pacific." At Trans Pacific they had no idea how the Catalina Direct part was to attach to their part, i.e threaded fitting or ???

This has all been somewhat of a surprise to me, since my recollection of the discussion here on the list was that the new "one-piece" stainless steel pipe was the way to go. It seems as though that this is in fact not a one piece part. Since it isn't, I'm not so anxious to replace the exhaust pipe. I've checked the pipe and it appears to be sound and well fitted. The only problem that I have is that the end fitting at the raw water inlet has developed a pinhole leak. I repaired it with epoxy in an overnight stop late last season, but don't want to rely on it for a full season. The part is about 6" long, has a threaded end that screws into the black iron pipe, has a 3/4" "Y" that the raw water hose clamps onto and a smooth end that the 1 5/8" hose clamps onto to take the wet exhaust to the muffler. Does anyone know where I can obtain this end fitting? Frank, Kik N Bak

Considerations

The part you're describing is similar to one I had made when the original exhaust on my boat failed due to corrosion at the weld between the 5/8 inch water injection pipe and the 1 1/4 inch nominal size pipe (actually 1 5/8 inch OD).

Rather than buy from Catalina, which can be a Border Customs nightmare for those of us in Canada, I had a local fabricator, who could weld stainless steel, make up the whole thing out of screw coupled, stainless steel, schedule 40 pipe. The only welding required was to connect the water injection pipe to the last pipe section.

Next time, if there is another, I'll use schedule 80 pipe for the last section where the water injection pipe is welded in. Schedule 80 pipe has a thicker wall but the same outside diameter. I'm fairly sure that the original Catalina exhaust was schedule 80 for the end section. There are two reasons for using the schedule 80 pipe: the hot gas and water form a fairly corrosive mix that attacks the weld heat altered steel and the screw threads remove quite a bit of the pipe wall reducing its strength perhaps too much.

By the way, I reused the coupling to the engine. It can be removed from the exhaust pipe but might require a lot of heat, a very large pipe wrench and a large mechanic's vice. The heat, and I'm taking about to dull red, makes the coupling expand loosening (a relative term) the joint. A couple of strong friends would be a useful addition for this part of the job. Charles Holder, Discover #617 (1988)

My suggestion would be to fabricate from schedule 80 stainless steel screwed pipe and bends. That way you only have to weld the injection pipe into the last short piece of pipe. I found the same piece rotted out frequently, probably due to heat alteration of the metal when welding and the presence of heat and salt water. Using screwed fittings enables one to replace one part and means a lot less expensive SS welding. Lots of pipe-fitters can cut and thread pipe. Two cautions: you'll need to use a thread sealer - I used regular exhaust paste spread on the pipe threads; welding in the injection pipe will distort the pipe section to out of round - have the welding done first, then the pipe cut and threaded. Schedule 80 is thicker than normal steel pipe and provides more metal after cutting the screw threads. As to which stainless steel grade, I'd suggest regular marine grade 18/8. Charles Holder


The exhaust flange for the Universal 25 XP is Part # 298599-R14. Make sure they install a rubber hose that has a hump to take up the vertical vibration stress. When I bought my Exhaust Manifold from the factory, they wrapped it with lots and lots of insulation. I'm not sure , but I think the main function is to protect YOU from getting burned. The pipe would run cooler if it had a place to radiate the heat. But I left all the wrapping in place. The results were such that it would not pass the "dollar bill test" that Ron use to talk about. That is, there must be a space between the manifold and the heat exchanger so the they would not rub each other and cause more problems. To solve that problem, the yard man took off the HX and bent the support flange about 1/2-1 inch so that there would be a good clearance. Dave Davis


As far as all the wrappings - they are there to keep all the HEAT inside the riser and not let it get into the interior of the cabin. TRIPLE check that the mounting flange on the engine to insure it is absolutely clean of old gasket material. Then check this again!! If the welding shop was capable of doing a good job of stainless welding, you should be good for another 5-10 years - if the rest of the flange piping is OK. Make sure that you have a slack bend in the raw water line that empties the heat exchanger water into the nipple in the riser. The tip from your mechanic is correct on worrying about a scored or pitted surface on either the engine / riser flanges. What I used for a "liquid gasket" material was muffler patch paste. It's the only material I know of that could stand up to the exhaust heat. Mine is sealed and w/o leaks, 3 yrs later. Ron Hill, APACHE #788


Detailed installation instructions #1

The first step in replacing your exhaust riser is to drain the coolant through the starboard side petcock near the front of the engine. Squirt some liquid wrench on the three nuts that hold the riser and flange to the back of the engine and let it sit over night. I believe these nuts are 7/16" and are best removed with a box end wrench rather than a socket, especially the one underneath. After you remove these nuts, you have to undo the raw water hose from the riser and the two clamps from the inlet exhaust hose to the muffler. With some gyrations the flange/exhaust riser will come out thru the engine compartment.

To reassemble the first step is to put the flange in a vise. Screw the exhaust riser into the flange until you get the angles aligned properly (use the old exhaust riser and flange as your pattern). Then back off the riser counting the number of turns until it is all the way off. With the flange still in the vise, treat the riser threads with some muffler patch and screw back in the flange the same number of turns. Remember don't over tighten because you don't want to have to back off (you may break your seal). You want to end up tightening it to get the proper angle.

Ensure that all of the gasket material is off of the exhaust/reservoir casting on the back of the engine. It's a real bear to get in there and make sure the surface is clean, but quadruple check this or you will not get a good seal and lose your coolant (when you refill) and have to start over with a new gasket. Make a dry run without the gasket just fitting the flange/riser assembly in place. As I mentioned in the Nov 98 Mainsheet Tech Notes, try the "dollar bill test." It's more important for a 25XP with the larger diameter heat exchanger than the M25, because the factory may have wrapped too much insulation in that area where the riser goes over the heat exchanger. I couldn't get the flange to completely seat until I cut out some of that insulation. If you can pass a dollar bill between the riser and the heat exchanger, you are in good shape. If you can't, whittle away some insulation.

Also measure the length of hose that you'll need between the riser and the inlet to the Aqualift muffler (with a new riser it may not be the same distance as it was with your old riser).

After you are sure the flange/riser is going to seat and that surface is absolutely clean, place the gasket on the three studs. I even used some of the muffler patch around both sides of the gasket to make sure I had a good seal. This is a perfect time to install the single hump hose which I wrote up in that same Mainsheet article and again in the Aug 99 issue( the 81/2" hose from the factory is $33.75).

Up to this point, disassembly and reassembly has been a one person job. Now you need a second pair of hands. As one person aligns the flange with the three studs on the back of the engine, the other person aligns and inserts the single hump hose into the flange and muffler inlet. Tighten down the three nuts to secure the flange, double clamp the single hump hose on the flange and muffler ends. When I attached the new raw water hose from the anti-siphon, I made it a little bit longer than the original factory installation so it could flex a little and put less strain on that welded nipple that goes into the riser. Re-clamp that hose and you are ready to refill the reservoir with coolant (50/50 Prestone).

To ensure that you don't have an air bubble in your internal cooling system that goes through the water heater, remove the inlet hose to the thermostat housing. Insert one of those Par Junior Pumps and with the pump exit pointed into the reservoir, keep pumping until you have coolant being pumped back into the reservoir. Remove pump and insert hose into the thermostat reservoir and tighten the hose clamp( you shouldn't have to "bleed" that system as all of the air has been purged) . Recheck that the reservoir is full & replace the cap, start the engine and check for any leaks. You should be in good shape. Hope this helps.

Ron Hill, APACHE #788


Detailed installation instructions #2

A "tech note" in the May 1997 issues of Mainsheet reminded me that periodic inspection of the exhaust riser was a good idea. To my surprise, cursory inspection under the vanity in the head revealed soot buildup on under the sink and on the interior side of the bulkhead to the aft stateroom -- not a good sign. It was a surprise because neither my wife nor I noticed or smelled diesel exhaust in the head or the main salon.

With Mainsheet article in hand, I called Catalina and discussed my options for replacement of the exhaust riser. Because hull #80 featured a black-iron riser as original equipment, it was recommended that I replace the riser with the black-iron version ($115). This recommendation was largely driven by the fact that the stainless steel riser used on more recent Catalina 34s results in the riser being centrally located between the interior bulkhead of the aft stateroom and the aft bulkhead of the engine compartment. (As I would later learn for "Flying Colors," the output of the upgraded riser was about 3" forward of the muffler input).

Ordering the riser was very straightforward, and was accomplished by telefaxing critical information including the desired riser material, hull number, and model year to Catalina. Catalina advised me that the flange and gasket for mounting the riser on my M-25 engine had to be purchased directly from the local Universal distributor.

To my delight, both the riser and the flange arrived within 7 days. However, as I would soon discover, the easy part of this job was over. Examination of the existing flange revealed that it was secured onto the exhaust manifold by three 9/16 nuts. While the top two nuts were easily accessible, access to the bottom nut was less than optimal and, of course, the bottom nut was the most seriously corroded and required the most attention. To improve access to the lower nut, I unfastened the heat exchanger mounting bracket (with heat exchanger attached), and lowered the entire assembly approximately 3 inches away from the riser. I found that access to the lower nut was then best accomplished through the large access panel under the aft berth. However, after several applications of liquid wrench, various wrenches, several sockets, and assorted vice-grips, I concluded that the lower mounting nut had become an integral part of the boat’s structure, and wasn’t going anywhere without greater leverage and persuasion.

Discussing the situation with a few very reputable marine diesel mechanics, I was consistently advised that my encounter with a frozen lower nut was very common. The consensus opinion was that I should remove the entire manifold with the riser still attached. Once the assembly was clear of the boat, I was able to remove the mangled nut by hammering a smaller socket onto the nut and applying torque by using a 2-foot socket handle. Persuasion worked! However, I soon learned that the entire flange had seized to the manifold due to an extensive rust buildup. A local engine shop was able to apply some heat with a blowtorch and remove the flange from the manifold by using a small sledge hammer. At this point, I employed the engine shop to clean the mating surfaces of the manifold. I also took the shop’s recommendation to remove the rusted mounting stud, and use a stainless bolt for attaching the new flange (the other two studs were in good shape). I had the shop screw the new manifold into the new flange - a good decision since it took two men, a vise, and two pipe wrenches to apply enough torque to screw the riser sufficiently into the flange.

Upon returning to the boat, I remounted the flange/riser assembly and utilized new manifold gaskets which my engine shop had been nice enough to cut. At the recommendation of the mechanic, I applied "Anti-Seize" to the nuts and bolt in order to help preclude the future seizure of mounting nuts and bolt. Upon remounting the manifold/riser assembly on the engine, I discovered that the new riser was misaligned with the inlet port of the muffler by about 3 inches. My choices were to remove the stainless riser and order a black-iron riser, or replace the muffler; I decided to replace the muffler. The boat’s muffler was the original box-type waterlift which measured approximately 13"x13"x10". The muffler was screwed and epoxied in-place on a piece of plywood which was form-fit to its base. After removing the mounting screws and breaking the muffler free from its foundation, I found that the height of the inlet and outlet ports severely restricted the muffler’s egress.

Consequently, I cut-off the inlet and outlet tubes, and was able to remove the muffler through the larger access port under the aft berth. The new muffler which I selected was manufactured by Veralift, and, similar to the old muffler, featured inlet and outlet ports on top of the unit (not a commonly used configuration anymore – it required a special order). However, unlike the old muffler, the Veralift was cylindrical in shape, with a diameter of approximately 8", and a height of 9". Consequently, it was convenient to work with, and I would later be able to install the muffler through the access door under the vanity in the head (i.e., I would work right-side-up! What a novelty!) As a foundation for the new muffler, I selected 3/8" marine plywood and cut it to a dimension of 17" x 13". I then aligned the plywood such that the 17" length ran fore/aft and overhung the forward end of the old foundation by 3". I then screwed the plywood onto the old foundation; the 3" overhang would allow for mounting the new muffler in alignment with the new riser. With the new foundation in place, I maneuvered the new muffler through the head-vanity access door and reconnected all hoses.

As I started the engine and checked all connections, I realized that my five-day adventure was almost over. The only other action would be to re-torque the flange bolts after a few hours of engine use.

Flying Colors #80


A Mainsheet letter written about draining the expansion tank is good advice and a good way to drain the tank. I have replaced my exhaust system twice and I only have this to offer. Using the drain plug does drain the tank however when you remove the gasket for the flange the remaining fluid will drain out the rear of the tank. If you use the drain plug the fluid (may) end up soaking into the engine compartment sound proofing. If you drain it from the rear it will fall onto the fiberglass and end up in the bilge. I also suggest taking this opportunity to wash the tank out to remove whatever particles have settled in the bottom of the tank over the last 11 years. Just a thought because you will have to replace the gasket no matter which way you go. You will also notice the gasket has a stamp on it indicating which side goes against the tank, (very important). Rich Dwyer, Rebellious #328


I did the draining today and caught maybe 95% of the coolant. I used a small plastic bendable cup and used my finger to stop the flow every time the cup filled up. I also spayed the the bolts with liquid wrench. Dave Davis