what happened to this engine? less than 50 hours

[Hermit Scott]

Some of you know about me rebuilding the YSM12 for my C30. I ran it for a couple of years, put about 50 hours on it and decided to rebuild a 2QM20 to replace it. I sold the YSM to a forum member here at SBO that lives in Houston. He drove up to pick up the engine and he, his friend and I took it out of my boat loaded in his truck and he took it home. Actually he took it to a mechanic to make a custom exhaust elbow, buy some motor mounts and touch up the paint. I hadn't ran the engine in 6 months or so when I went to the boat to meet the buyer and take the engine out. As always it started up right away. Understandably the buyer wanted to see the engine run before buying it.
We were standing in the boat, I was getting ready to shut down the engine, I shut the water off, went to throttle it back and shut it down. One of the guys said "can you just back it out and turn it around under power". I said sure. I went up to back the boat out. Smoke started coming from the cabin and I realized what I had done. I went down and turned the water back on. The temp gauge said it was still normal temp, about 20 degrees above what it usually ran at. We waited 20 minutes with the engine running to make sure water was flowing through the exhaust again and clear out the smoke from the cabin. When we started taking the engine out, the exhaust elbow fell apart at the solid part near the engine. It just literally lifted up like it wasn't connected. We looked in the elbow, it didn't look corroded but something was obviously wrong with it.
The mechanic has had it for two months or so. Yesterday he said the motor was locked up and took the head off to see why, and this is what he found. He claims the motor had been submersed in water prior to him receiving it.
The buyer says there are no engines outside at the warehouse.
The buyer is going to the mechanics shop tomorrow to talk about it. The mechanic is under the assumption that this engine looked like this leaving my boat. I don't believe an engine could run like this or any where near this condition.
I thought it was astronomical odds that this engine ran flawlessly for 2-1/2 years and the moment I am standing there selling it, the exhaust elbow broke off. What else could have happened to this engine immediately after running perfect for 2-1/2 years, we turn it off and now it looks like this two months later? Cracked block or cracked head as we shut it down?

In your opinion what happened to this engine?

 

[Tim R.]

My theory is that when the exhaust riser failed it allowed water to run back into the engine thru open exhaust valves which when sitting for a few months would rust, thus locking up the engine.

The exhaust riser was probably on it's way out and your grabbing it finished it. Less than 50 hours tells me the engine never got a chance to fully heat up and dry out each time it was used which caused more stress on the exhaust.

I would never store an engine for two months with the exhaust manifold open to the environment. Condensation could form and cause something like this.

Back when I was racing, we would buy engines from running cars and immediately remove the valve cover, to adjust the rockers in order to close all the valves and then pickle the cylinders thru the spark plug holes.

I would say this is a failure on the buyer's part to properly seal the engine.

BTW, why did you shut the intake before shutting down the engine?

 

[Bill Roosa]

Well you shut off the cooling water flow and the exhaust and manifold HE got hot. You then turned on the cooling water causing a thermal shock. Cast iron is not good at handling thermal shock. hence the exhaust breaking off. The exhaust manifold also cracked and allowed coolant or seawater into the engine exhaust valve.
As one of those principal rules that you NEVER break. don't turn the cooling water off while the engine is running.

 

[sailaway78]

Agree with previous posts

There was some combination of bad manifold and the heat from no water, and shock of cold water that allowed sea water into the cylinder via exhaust valve. It doesn't take long for salt water to totally destroy a cylinder liner/piston.

 

[Hermit Scott]

I always closed the valve then immediately choke the engine to shut it off to minimize any additional water through the exhaust. I also never let the engine sit after shutting it down with out closing off the seacock for fear of water filling up the engine because it is sitting below the water line.
The elbow didn't break where there is water. It broke an inch or so from the flange that it is bolted to and about two inches from the water injection elbow. The solid elbow bolted to the head is a separate piece from the injection elbow that is bolted to it, the solid elbow is the piece that broke. I did ask the buyer about the elbow, he said he intended to replace it anyway with a new one.
The water jacket of the engine was always full of water. The engine didn't overheat but the exhaust elbow did. Looking back it seems pretty easy to get a little bit of seawater in one of the ports. He took it to a mechanic right away, but told the guy he was in no rush to get it painted,the exhaust elbow installed and checked out because he was still working on the engine compartment.

 

[Hermit Scott]

Less than 50 hours tells me the engine never got a chance to fully heat up and dry out each time it was used which caused more stress on the exhaust.

I never just ran the engine at idle. If I wasn't taking the boat out I put it in gear and pushed the dock to get it up to temp. I was more concerned with glazing cylinders from leaving it running at idle.
I may have put more than 50 but no more than 100. we mostly used the boat at the dock and didn't take it out. So if we went for a weekend and didn't take it out, it would get ran about an hour at the dock.

 

[Stu Jackson]

I always closed the valve then immediately choke the engine to shut it off to minimize any additional water through the exhaust. I also never let the engine sit after shutting it down with out closing off the seacock for fear of water filling up the engine because it is sitting below the water line.

Uhm, Scott the purpose of the vented loop on the water injection hose between the HX and the riser nipple, right before it hits the exhaust (air) riser, is to prevent just that. You did install a vented loop, did you not?

One of our respondents posted a photo from a reference source about how to install a diesel under the waterline. Wish i knew where the post was, but if you do some research you can find it. I'll look, too.

Here's one, from a Google on diesel engine vented loops, no pictures, but a good description: http://www.marinemechanic.com/site/page66.html

 

[RON20406]

Your question was answered correctly by Tim and Bill . . . simple. Good luck and good sailing, Ron

 

[higgs]

I'm with Bill. Worse thing you can do to an overheating engine is to give it cold water.

 

[Hermit Scott]

Uhm, Scott the purpose of the vented loop on the water injection hose between the HX and the riser nipple, right before it hits the exhaust (air) riser, is to prevent just that. You did install a vented loop, did you not?

One of our respondents posted a photo from a reference source about how to install a diesel under the waterline. Wish i knew where the post was, but if you do some research you can find it. I'll look, too.

Here's one, from a Google on diesel engine vented loops, no pictures, but a good description: http://www.marinemechanic.com/site/page66.html

I had a bronze one with a plastic 'scot' check valve brand installed. But the plastic check valve was very brittle and cracked so I didn't trust it and I took it out. Then I didn't trust that water would not seep through the impeller and fill up the engine, so I always kept it closed off when not running. The engine is raw water cooled so there was no HX. And that is why I was concerned about the water jacket. It's a 40 year old engine that has had sea water in it it's whole life. When I had it all apart I didn't see any areas that concerned me though. No thin walls or anything.
The mechanic thought the whole engine was submersed by what he saw in the cylinder. It was probably just a small amount of water in the cylinder sitting for 2 months. The rest of the engine should be fine.
Hopefully all this will need is a new piston and cylinder liner. I am going to ask for some pics of the head tonight. The parts will be $300 or so, piston, liner and head gasket.