Mysterious Engine Failure

[LeighWebber]

More comments:

Tin Tin - the water pump">raw water pump is gear-driven, so no v-belt involvement. FWIW, the v-belt was fine afterwards. Exhaust elbow hose popped off? No, it was firmly attached. You are getting warmer, though.

IOM - I will defer commenting for the moment. All will be clear shortly.

Jim Cate - I did all those tests afterwards, as I will explain shortly.

Chris Mac - the v-belt was in perfect condition afterwards.

King Richard -- good idea. See below.

[LeighWebber]

Here's the solution.

After cleaning and inspecting everything, I went to the cockpit to try starting the engine. The engine compartment was still wide open, and I asked my 16 year-old son to watch the engine. It started instantly. I looked over the stern – no water coming out of the exhaust. I dashed back to the instrument panel and hit the stop button just as my son yelled that there was water squirting out of the engine. I jumped down below and saw water coming out of the base of the exhaust riser, underneath the fiberglass insulation packing. I wiggled the exhaust riser and found that it was broken clean through! I unwrapped the insulation, and saw that the pipe was broken just above the 90-degree bend that connects the riser to the exhaust manifold. On the Beta, the exhaust manifold opening is at the back of the engine, near the heat exchanger. The exhaust riser pipe is stainless steel, about 2 inches in diameter. There is a 90-degree bend close to the attachment flange, then a straight vertical run of about a foot to the mixing elbow. The mixing elbow is then joined to a length of exhaust hose that leads down to the water lift muffler.

There is a factory weld that joins the vertical exhaust riser to the 90-degree fitting at the flange. The factory weld held just fine: the break occurred about an inch above it. The break was rather jagged – not straight across. Fortunately, my local welding shop says they can repair the pipe. I’ll also order a spare from Beta.

So here’s my diagnosis. The exhaust pipe cracked during my recent long passage. On the day of the incident, it broke right through. The break was concealed by the fiberglass insulation wrapping, so I didn't notice it. The smoke was not from a fire – it was black diesel exhaust. One of you suggested that when I backed away from the dock, the dinghy blocked the exhaust at the stern. Not sure the relative geometries would allow that, but it's possible. If it did block the exhaust, then that would force diesel exhaust through the broken riser and into the engine compartment. The engine air intake is about 4 inches away from the base of the exhaust risher, pointing right at the place where the break occurred. The escaping exhaust went straight back into the engine, producing the black smoke. With no exhaust pressure going up the pipe, the sea water flowing to the mixing elbow was not being forced out to the muffler. The easiest path for it was back down the exhaust riser. I didn’t notice the water on the day of the incident because I thought it was a fire. By the time the smoke had cleared, of course, the water was no longer dripping. It was only the next day when my son saw the water gushing out. The exhaust riser/elbow is at the welding shop at the moment, but as I think of it, I think the sea water exit hose attaches to the elbow pretty much at its highest point, which is a bad design/installation. It should be attached on the downhill slope of the elbow to prevent water from flowing back down the exhaust riser. I won't know for sure till I get the part back on Monday.

I am still puzzled by a couple of things. First – why did the riser break? The exhaust riser and mixing elbow is held in place by a 1.25 x 3/16” steel strut bolted to the engine and attached with a steel strap looped around the insulation near the mixing elbow. Engine vibration should therefore be transmitted to the flexible exhaust hose: the engine and exhaust riser/mixing elbow would be vibrating together, so there should not be any stress on the exhaust pipe. I noticed, however, that the strap had worn away much of the insulation on the pipe. This may have allowed the pipe to vibrate independently of the engine, probably on a harmonic, leading to the fracture.

Second – why was there black smoke? Before I saw your excellent responses, I couldn't figure this out. It's obvious, however, that the escapting exhaust fed straight into the air intake pretty much eliminating combustion oxygen. When you look at the air intake breather, it almost looks like it's designed to suck in exhaust fumes!

Third – why didn’t water get into at least one cylinder and cause a hydro lock? When I started up the engine post-cleaning, there must have been water in there from the incident. I count myself very lucky that there was no hydro lock, which could have caused terrible damage (connecting rods, bearings, etc.). If I had known what the problem was, I would have removed the injectors before cranking with the starter. That’s what I will do before I start the engine again.

Further comments and suggestions welcome.

[LeighWebber]

Follow-up. When I tow my little Zodiac, I use a double tether. One goes to my boat's port after cleat, the other to the starboard. This keeps the dink nicely centered in my wake and very stable.

Just checked the dinghy and boat stern geometry. If I snug the lines in tightly the bow of the Zodiac fits perfectly against the exhaust outlet on my stern! Going astern like that would be like putting a cork in the exhaust. IOM you are a genius.

The riser probably fractured on my long trip (maybe when I opened the throttle wide for 15 minutes), but the engine rpms produced enough pressure to blow most of the exhaust out the normal way. When I backed out of my slip with the dinghy snugged in, the blockage caused the exhaust to leak (big time) into the air intake breather.

Takeaways.First, snug your dinghy off to one side so as to prevent it getting near the exhaust outlet.

Second - add a step to your morning checks: grab the exhaust riser and see if it is loose. Yeah, slim chance, right? But it happened to me, and could have been far worse.

Third - don't move the boat until you track down the source of any unexpected water in the bilge.

Fourth (and I think I got this right) - if thick smoke pours out of your engine compartment, stop the engine and empty your fire extinguisher in there immediately. Don't ponder the possibilities, just do it. The cleanup was a PITA, but think of what might have happened were it a real fire.

Thanks again for all the comments.

[skipperpete]

I guess you have this swan neck and if so,there’s a vague possibility that your’e not completely free of this problem even if you replace it. In answer to your question, it probably broke because the exhaust hose to the aqualock is too stiff and is applying pressure against the vibration of the engine, the next thing to crack open is the weld between the riser mounting block and the exhaust manifold, mine did this on a previous boat. A softer silicone exhaust hose or maybe a hump hose will absorb the vibration but risers like yours are always prone to failure unless properly supported, usually with a strut to the flywheel housing or gearbox.

[IOM]

I have no clue what your Exhaust looks like, but I do know stainless steel is an untrustworthy friend.
It's wonderful in its ability to resist corrosion, but it reputation to cracks for vibration and repeated heat cycling is terrible.

The worst time for engine movement is at switch off and start up. So the last run you did, may have just about have completed the crack, and either the switch off or the start up could have broken the pipe completely , or even bumping into the dingy.

I assumed the pipe just came off because the few boats I have seen have some pretty dodgy pipe connections on the exhaust (IMO)and a little to much back pressure could cause them to fall off ie like the dingy blocking the outlet

Black smoke is over fueling. Either too much fuel or too little air. Since the fuel is constant by virtue of the pump and throttle and controlled independently of air, removing the oxygen provides a very rich mixture and the associated black smoke, also common if a turbocharger fails. Only in the turbo case, continued use of the engine can lead to total engine failure. A little black smoke is OK , but a lot is good reason to back off the power to prevent engine failure.

The black mess combined with your powder must have made for some wonderful recreational cleaning inside the engine compartment and the bilges.

There are better options of fire suppressant than powder as a first solution to a fire.

I have seen one that is literally a pressurized plastic pipe with a small pressure gauge on the end, filled with a fire suppression liquid , and used in computer system rooms. The guy had it tied to the top of his engine, so it never went off for just heat, but fire would cause the pressure to rise and the pipe to soften and burst at the point where the flame was, depositing the liquid where the fire originated. I believe its common in the computer world, but I haven't been able to find it yet.

Fire Stryker also make a solid state non servicing extinguisher. I have thrown it into a fire and closed the lid and left it with success , but you could also push it into a 35mm hole in the engine room and leave it do its thing without ever even opening the engine bay. for their size and weight these are pretty incredible devices and not much more expensive than a size for size fighting capacity powder extinguisher

There is also a marine fire fire retardant system I saw locally at a show that is plumbed around the engine bay, and triggers automatically (or manually) to spray retardant all over the engine bay at regular intervals without opening the engine bay and adding oxygen.

All these systems leave no damaging residue like the powder.

[LeighWebber]

All your suggestions are completely new to me -- thank you for listing some of the alternatives. My hunch is that most rec boaters have no idea about any of this stuff. I consider myself to be a fairly seasoned sailor, but I confess to have never given adequate thought to fire suppression. I will be researching your suggestions.

Fortunately my little Beta 25 is not a turbo, so it simpy gagged on all the CO in the exhaust and lost all power. When I get the repaired part tomorrow I will run the engine for a while, then change the oil. I'll post pix of my "swan neck" riser and mixing elbow so everyone can see what I have been talking about. I also plan to pick up some exhaust pipe repair gizmos (clamps, tape, etc.) against the time when this happens again. They are cheap insurance.

I still don't know why the sea water flowing into the mixing elbow ended up squirting out at the break in the riser. If the geometry of my swan neck allows the water to flow back down the riser, I may get a custom part made with the sea water fitting way down the slope towards the water lift muffler. Sea water flowing into the exhaust manifold would be the biggest threat of all in this scenario.

[FPNC]

Originally Posted by LeighWebber

If the geometry of my swan neck allows the water to flow back down the riser, I may get a custom part made with the sea water fitting way down the slope towards the water lift muffler. Sea water flowing into the exhaust manifold would be the biggest threat of all in this scenario.

The typical Beta stainless riser design only injects water at the very bottom end of the elbow where the hose connects. If you had water back up the riser elbow is was due to the back pressure from the dingy blocking the exhaust outlet. If you block the outlet the water and exhaust have no where to go except backwards towards the engine.

[skipperpete]

Originally Posted by LeighWebber

All your suggestions are completely new to me -- thank you for listing some of the alternatives. My hunch is that most rec boaters have no idea about any of this stuff. I consider myself to be a fairly seasoned sailor, but I confess to have never given adequate thought to fire suppression. I will be researching your suggestions.

Fortunately my little Beta 25 is not a turbo, so it simpy gagged on all the CO in the exhaust and lost all power. When I get the repaired part tomorrow I will run the engine for a while, then change the oil. I'll post pix of my "swan neck" riser and mixing elbow so everyone can see what I have been talking about. I also plan to pick up some exhaust pipe repair gizmos (clamps, tape, etc.) against the time when this happens again. They are cheap insurance.

I still don't know why the sea water flowing into the mixing elbow ended up squirting out at the break in the riser. If the geometry of my swan neck allows the water to flow back down the riser, I may get a custom part made with the sea water fitting way down the slope towards the water lift muffler. Sea water flowing into the exhaust manifold would be the biggest threat of all in this scenario.

I have a possible explanation for why you had seawater flowing in the wrong direction (against the exhaust gas flow).
After the raw water enters at the injection point it normally mixes with a high speed gas flow and then goes directly into the aqualock but without the gas pressure to eject the water, the aqua-LOCK becomes a bit of a dead end for the in rushing seawater so it takes the path of least resistance back towards the break in the riser. I don’t think you were in a situation where the water could actually get into the exhaust manifold either with the engine running or shut down, it would all exit at the fracture ….even just cranking.
Make sure the support strut is really tight and properly adjusted and probably not over the insulation unless its really well secured, that braided insulation tape doesn’t do well if something is continuously chafing at it.

[AA3JY]

Originally Posted by LeighWebber

I still don't know why the sea water flowing into the mixing elbow ended up squirting out at the break in the riser. If the geometry of my swan neck allows the water to flow back down the riser, I may get a custom part made with the sea water fitting way down the slope towards the water lift muffler. Sea water flowing into the exhaust manifold would be the biggest threat of all in this scenario.

There possibly be an anti-siphone valve in your circuit?