Troubleshooting a seized Yanmar engine

[Waterant]

Hi guys,

I need your help to figure out the next step in getting one of my engines (Yanmar 6LYA-STP) back to life.

What i have now:

- The engine is seized (I can not move the engine shaft at all using 30" bar on the front wheel nut). I can do it easily on the second working engine.

- I do not know what happened as the previous owner passed away and took this information with him

- I removed the raw water pump and starter to ensure those are not frozen, causing this issue. Both are in good condition with no sign of rust or damage

- I drained the oil, and there was a little water it in (~30 oz/1L in 5Gal of oil) which seems like a negligible amount but is still worth mentioning

- I removed the heat exchanger (mostly to be able to remove the starter) and there is no damage or corrosion there.

- I drained ~4.5 gal of antifreeze which is how much the engine holds, so there was probably no leak of antifreeze to the oil

- I removed all injectors, and there is no visible corrosion or damage on them

- I removed the valve cover and do not see any apparent damage or anything suspicious there (see image attached)

- I hit every valve with a rubber mallet, and all but 2 sets are making a nice high sound. on 2 cylinders (1 and 4 or 5) the sound is different like valves are not moving there. I'm not sure if this is because of the position of the pistons in the cycle there or those may be the frozen ones

- I put mystery oil for a month in every cylinder via the injector's hole.


So, my question: is there anything else I can test/check without removing the cylinder head?


and second more general question - is there even a remote possibility to find and fix the problem like that without removing the engine or I should stop the madness, take it out and send it to the shop?
It's not a question of what is faster, I'm not in a rush, but if there is no way to fix a problem like that in the boat, I may very well save time and start looking for a shop.

 

[GoneFarrell]

Buy or rent a bore scope to peek in the cylinders?

30 oz of water in the oil does not give me the warm and fuzzies. Likely head gasket issue from an overheating problem?

 

[Waterant]

good idea on the borescope. thanks
i have one but it's 2mm too thick and does not fit. I'll buy a smaller diameter one to get inside.

> Likely head gasket issue from an overheating problem?

can it cause the engine to seize up?

 

[twistedtree]

A liter of water i the oil is not insignificant. It’s a HUGE amount of water. There should be zero water. None. Absolutely none

Any idea if it was salt water, fresh water, or coolant? Has the bot been operating in salt or fresh water? You say your coolant wasn’t low, so I’m guessing wasn’t coolant in the oil. That means it’s seawater, probably indicating a poor exhaust system design. If it’s fresh water and the boat normally operates in sea water, then perhaps someone improperly did a fresh water flush and drowned the engine.

Oh, is there a sea water oil cooler for the engine oil? That could be a path for water into the oil, however I don’t think I’ve ever heard of a seawater engine oil cooler.

What’s a bit odd is that the most common entry point for water is backing up through the exhaust. But that dumps water into the intake and exhaust, not the crankcase. Really the only path for water into the crankcase from the intake and exhaust side is past the piston rings, and that would be a slow process.

You might dip a dowel down each cylinder through the injector ports and see if any come up wet. It’s almost certain that water got into the engine somehow, and it’s just a question of the extent of damage. It sounds like new pistons and sleeves are a neat certainty. Depending on the installation, it might be possible in situ rather than pulling the engine.

At this point I think the next step after the dowel dip will be to pull the head. Or get a bore scope in there looking for rust.

 

[sunchaser]

Getting the engine repaired and running is job one, but ---

If there hasn't been an overheat, suspect backflow from the exhaust side, failed elbow or a leaking after cooler. As has been discussed on TF and other forums for a very long time, back flow from exhaust runs is way too common on some builds. Check the oil for type of water, fresh, salt or coolant.

Which means get the cause remediated too.

 

[Waterant]

Any idea if it was salt water, fresh water, or coolant? Has the bot been operating in salt or fresh water?

I do not have this information and already disposed of the oil.
The boat was kept in the river, which has tides, so i think it was a mix of fresh and salt water.

Oh, is there a sea water oil cooler for the engine oil? That could be a path for water into the oil, however I don’t think I’ve ever heard of a seawater engine oil cooler.

it's a seawater oil cooler. same one got frozen on the other engine, which caused the cups to deform and was leaking. I'm waiting for new cups to fix it. It seems fine on this seized engine; there was no water inside when i tried to drain it. i guess it could be a good idea to pull it out an send for inspection.

What’s a bit odd is that the most common entry point for water is backing up through the exhaust. But that dumps water into the intake and exhaust, not the crankcase. Really the only path for water into the crankcase from the intake and exhaust side is past the piston rings, and that would be a slow process.

That engine was sitting in the water up to the top of the oil pan for a short time so maybe some water could get thru the dipstick hole.

I also heard about a common problem on Mainships with the engines' hydrolocking because of the poor exhaust design.
so this could be the original cause for this engine getting seized in which case i would probably see bent piston leg or valves.

At this point I think the next step after the dowel dip will be to pull the head. Or get a bore scope in there looking for rust.

Got it. Thanks.
borescope it is.

 

[DavidM]

I had that same engine on my last two Mainships: a 34T and a Pilot 34. Here are my thoughts:

Like many others have said, one liter of water is way too much.

If sea water got in through the exhaust, then it may have happened all at once or maybe over time. The valve gear looks great, no rust so it may have happened all at once. A big slug of water came in through the exhaust due to low water line clearance and the way the boat was moored, stern to the waves which pushed water up inside. Then it hydrolocked the next time it was started.

That could have bent a connecting rod or it could have stopped while cranking after a revolution or so. If the latter then you should be able to turn it over after removing the injectors. That happened to me on my Pilot 34 after water sloshing up the exhaust occurred on a travel lift. After clearing the water out, I changed the oil a couple of times and it was fine after that.

But it is possible that water either got in over time or the PO tried to start it, it hydrolocked and it sat there for a good while until the rings rusted and locked up the engine. You could do an oil analysis if you still have the old oil. High sodium with moderately high potassium is a sure sign of seawater in the oil.

So first question- have you tried to turn it over after the injectors were out? If you tried and it was still locked up then it either it is rusted rings or much worse, a bent rod.

I would first confirm the question above then if it is still locked then squirt in a bunch of WD40 or equivalent into each injector hole and try again after sitting for a day or so. If that doesn't work then I suspect you are in for a tear down job.

I just reread your first post so it is doubtful that WD40 would do any better than Marvel Mystery Oil. It is now looking like a tear down, and I would pull it and do it in a shop with a good mechanic. There is one compromise: pull the head with the engine in place and try again with WD40 or MMO. That eliminates the valve train as being stuck, but that is not usually the case in these situations.

David

 

[twistedtree]

Just for clarity, I'm asking about an engine oil cooler, not the transmission oil cooler. The transmission cooler would typically be sea water cooler, but I don't think I've ever heard of an engine oil cooler that is sea water cooler. They are typically built into the engine and are cooled by the engine coolant.



I didn't realize the boat had been flooded, so I agree that could be the source of the water in the oil pan, and might be unrelated to the seizure. But the seizure has all the signs of water intrusion into the cylinders, so that needs to be investigated fully.

 

[Waterant]

Just for clarity, I'm asking about an engine oil cooler, not the transmission oil cooler. The transmission cooler would typically be a seawater cooler, but I don't think I've ever heard of an engine oil cooler that is sea water cooler. They are typically built into the engine and are cooled by the engine coolant.

I'd prefer to have as little as possible of seawater around the engine, but the oil is seawater-cooled on this engine
if it was coolant-cooled, it would not freeze in the winter, and i would already save $400 on new cups and 3 days of making yoga love to the engine trying to take it out.

Fig 15 on this chart is the oil cooler:
https://yanmarshop.com/en-GB/catalo...-small-ly-series-6lya-stp-fig-23-cooling-pipe

 

[Waterant]

It is now looking like a tear down, and I would pull it and do it in a shop with a good mechanic. There is one compromise: pull the head with the engine in place and try again with WD40 or MMO. That eliminates the valve train as being stuck, but that is not usually the case in these situations.

i think you are right but i will try to pull the head out first to make sure i know what has to be fixed. my hope is to get to the smallest possible part (engine block?) which has to be removed and sent for repair which will solve a whole bunch of problems with taking the whole engine out.
it's 1200+ LB and getting on top of it will require a very long forklift which the marina here does not have or some kind of railing to get it to the edge of the boat. the time to set it up will probably be the same as the time to tear it down to the block inside the boat.
I see another problem with getting it back together later but enough swearing and sweating can fix everything and I prefer to solve the problems in the order of appearance

 

[Waterant]

Which means get the cause remediated too.

Thanks. That is also on my mind. I read somewhere Mainships have a problem with the engines' hydro locking due to the poor exhaust system design.
This is something i will need to investigate in more detail.
if I end up getting the engine out of the boat, it may be a good time to get to solving that problem as well.

 

[DavidM]

Actually I have not read anything about MS 430s having exhaust geometry problems. They may have sufficient clearance (usually 12+") above the water line or they may use an equalizing line like my 34T had. It went from the bottom of the lift muffler out the side near the water line. This meant that the water in the lift muffler could never get above the water line level, eliminating any chance of getting into the turbo.

I am surprised more trawlers don't use this simple fix.

My Pilot 34 had a horizontal muffler so the equalization line wouldn't work. I modified the exhaust to add 8"of rise. Fairly easy to do if you have sufficient overhead clearance for the higher riser.

David

 

[Waterant]

Actually I have not read anything about MS 430s having exhaust geometry problems.

that's good to hear. maybe my problem is not with a hydro lock and bent rods or valves which will be nice. i little rust i can handle

 

[SoWhat]

A borescope is your friend.

Try a 5' breaker bar and rock it to the extent possible. There aren't too many things that can seize an engine so I suspect you will be taking the heads off in short order. Start soaking bolts around exhaust with PB Blaster or Kroil. It will make removal easier.

 

[sunchaser]

A failed after cooler or exhaust elbow will allow water into the top end. When was the after cooler last serviced? Open up the discharge side of the turbo and any rust and scale buildup there hints at water going the wrong way.

 

[Waterant]

A failed after cooler or exhaust elbow will allow water into the top end. When was the after cooler last serviced? Open up the discharge side of the turbo and any rust and scale buildup there hints at water going the wrong way.

I do not think aftercooler was ever serviced. Engine has only 280 hours on it so they probably never get to servicing it.
Thanks, I'll check the turbo.

 

[Waterant]

A borescope is your friend.

Try a 5' breaker bar and rock it to the extent possible. There aren't too many things that can seize an engine so I suspect you will be taking the heads off in short order. Start soaking bolts around exhaust with PB Blaster or Kroil. It will make removal easier.

A borescope is coming tomorrow.

I'm afraid to put too much force on it. With 5' breaker and my unintelligent power of a 6'2" beast I'll probably break the crankshaft or whatever that little nut is connected to

I will do pb blaster, thanks

 

[twistedtree]

I'd prefer to have as little as possible of seawater around the engine, but the oil is seawater-cooled on this engine
if it was coolant-cooled, it would not freeze in the winter, and i would already save $400 on new cups and 3 days of making yoga love to the engine trying to take it out.

Fig 15 on this chart is the oil cooler:
https://yanmarshop.com/en-GB/catalo...-small-ly-series-6lya-stp-fig-23-cooling-pipe

Thanks. Learn something new every day. So that cooler failure could be another source for the water in the oil pan.

 

[Jeff F]

If it was ever running with water in the oil I would think you'd see lots of evidence on the valve train and elsewhere from the emulsified mix.

Sent from my moto g play (2021) using Trawler Forum mobile app

 

[Waterant]

If it was ever running with water in the oil I would think you'd see lots of evidence on the valve train and elsewhere from the emulsified mix.

Good point. Thanks for that. Everywhere I saw so far the oil is usual nice black

 

[sunchaser]

I do not think aftercooler was ever serviced. Engine has only 280 hours on it so they probably never get to servicing it.
Thanks, I'll check the turbo.

If you peruse boatdiesel.com or seaboard marine you'll see the term marine age. Irrespective of hours your after coolers should be pulled, pressure checked and serviced every 3-5 years. A failed after cooler will definitely hydro lock an engine.

 

[rgano]

I am familiar with a few of the more prevalent diesels used in trawler propulsion, and have never seen anything but raw water cooled lube oil coolers. I would be interested to hear of the engines which are otherwise arranged. Always learning...

As an aside, my Yanmar has an internal lube oil cooler with diesel fuel as the coolant in addition to the external raw water cooler - then of course there is the return diesel fuel cooler....

 

[sunchaser]

I am familiar with a few of the more prevalent diesels used in trawler propulsion, and have never seen anything but raw water cooled lube oil coolers. I would be interested to hear of the engines which are otherwise arranged. Always ...

Some Cat and Perkins Sabre diesels have coolant cooled/heated lube oil utilizing a plate heat exchanger mounted on side of engine.

 

[vacser]

Is your transmission still connected? Could your tranny be seized?

 

[Jeff F]

I am familiar with a few of the more prevalent diesels used in trawler propulsion, and have never seen anything but raw water cooled lube oil coolers. I would be interested to hear of the engines which are otherwise arranged. Always learning...

Cummins BT and JD 4045/6068 have coolant oil coolers. My assumption has been that it's common on modern engines. Lots of benefits IMO but that's for another thread [emoji12]

Sent from my moto g play (2021) using Trawler Forum mobile app

 

[mickand]

"Just for clarity, I'm asking about an engine oil cooler, not the transmission oil cooler. The transmission cooler would typically be sea water cooler, but I don't think I've ever heard of an engine oil cooler that is sea water cooler. They are typically built into the engine and are cooled by the engine coolant."

Be careful with this statement - a lot of marine diesels including mine have engine oil coolers where the main raw water pump sends external water be it salt or fresh through the cooler.

 

[mickand]

My other thought is that it's just the pistons/rings seized in the bores. You'd be very unlucky to have a bent rod. I'd take the head off anyway - if nothing else you'll have eliminated a head gasket issue - then fill the bores with a good penetrant and let it soak for days - then try barring it over again.

 

[twistedtree]

I am familiar with a few of the more prevalent diesels used in trawler propulsion, and have never seen anything but raw water cooled lube oil coolers. I would be interested to hear of the engines which are otherwise arranged. Always learning...

As an aside, my Yanmar has an internal lube oil cooler with diesel fuel as the coolant in addition to the external raw water cooler - then of course there is the return diesel fuel cooler....

My experience is with Cummins QSC, Deere 6090, Deere 4045, and Scania DI 13. All have coolant-cooled engine oil coolers. The Yanmar in this thread was the first raw water cooled engine oil cooler that I have seen.

 

[twistedtree]

"Just for clarity, I'm asking about an engine oil cooler, not the transmission oil cooler. The transmission cooler would typically be sea water cooler, but I don't think I've ever heard of an engine oil cooler that is sea water cooler. They are typically built into the engine and are cooled by the engine coolant."

Be careful with this statement - a lot of marine diesels including mine have engine oil coolers where the main raw water pump sends external water be it salt or fresh through the cooler.

So I am learning. I'd be interested in other examples of raw water cooled engine oil coolers.


I have always presumed that an oil cooler would be equally a part of non-marine engine applications, so cooled in the same way across all engine applications. But apparently that's only the slice of the world that I have seen.

 

[ronobrien]

Here is a page from Amazon for bore scopes. These are quite effective and fairly cheap. I bought the $100 one with both front and side camera heads, but I am a bit of a tool junky. https://www.amazon.com/Best-Sellers-Borescopes/zgbs/industrial/401578011