Yanmar 2GM20F suddenly lost power but not RPMs

[scorpio77]

Hi all folks, Im looking for some experience Yanmar owners, about a month ago I purchased a beautiful ODay 322, with a Yanmar 2GM20F working flawlessly, a couple of days ago while returning from the sea to San Diego Bay, it was late and the wind was not cooperating at all, so I stowed sails an turned on the engine, after motoring for a while at 4-5 knots, the boat lost speed until just 1 knot, I reviewed the engine RPMs, being ok, accelerating and decelerating normally, but apparently the propeller was not getting the power and I heard a noise like if it was skidding, then I looked at the boat sea water discharge and suddenly it started to expel dirty black water for a while, so I shut down the engine, then I checked the oil and coolant, being both at the full marks and with no leakage at all.
So I hoisted sails again and managed to sail to the marina, arriving around 11 in the night.
Before entering the Marina, I started the engine again, hoping to have it available for the docking in the night, It started nicely, I put some thrust in it, getting two knots, so I decided to accelerate it more, and surprisingly it worked ok getting the normal 4-5 knots as if nothing have occurred before, no more black water, no more skidding noises.
The next morning I took it out to the bay briefly just to make a quick revision of the engine and it worked apparently ok.
Has anyone of you folks have an idea of what could happen to the engine, I would appreciate your help to get this matter solved.

Jose Salgado
ODay 322 1987
DREAM ON

 

[Delezynski]

What comes to my mind is you might have picked up a plastic bag in the prop. As you sailed in it managed to drop off. If the problem does not come back, that was most likely it.

The other option might be a failing drift pin in the transmission to shaft coupling. It that is it, it will come back soon. But you most likely would not get the black soot in the exhaust water.

Greg

 

[Stu Jackson]

Did you recently have any trouble starting and perhaps needed to crank for an extended period? If you have a water lift muffler, it may have been full. If you do, check the antisiphon valve at the water inlet if you have one. Also check you raw water impeller.

Sometimes when that kinda stuff happens, it pays to stop and put the engine in neutral, and then in reverse, sometimes it knocks whatever is there off.

 

[scorpio77]

Hi Stu, the engine was starting at the first touch of the starting button, no problem at all with that, anyway I will check the lift muffler for water inside, but it does not have an anti siphon valve.
I recall that when the boat lost speed and I was trying to find what was happening to the engine, I switched to reverse then to forward and in that moment the black stuff started to came out from the exhaust, exactly as you say.
Also, I am confused with what You say Greg, the drift pins are connected to the exhaust? Im lost here.

Jose Salgado
ODay 322 1987
DREAM ON

 

[Delezynski]

Jose,

Sorry for the confusion. The pin I am speaking of is a pin or key that fits in a grove on the prop shaft and in the transmission coupling. It makes the shaft turn with the transmission.

I have had one shear due to an out of alignment condition.

Once this pin shears, the engine sounds like everything is fine, but the prop no longer turns. But it might stick a bit and seem OK, until it's pushed a bit hard.

Just an idea.

Greg

 

[scorpio77]

I got the idea Greg, makes sense to me to explain the skidding sound and lost of propulsion, and after a few hours of having shut down the engine, it maybe stick again for a while.
This has to be related with a bad alignment, the next day in the morning I noted that the engine was rocking a little bit, in your experience is this normal for this engine? or it has to be running smoothly while engaged.
About the black stuff in the exhaust, a friend just tell me that the mixing elbow could have been clogged in the point where the two conducts converge, the exhaust manifold and the raw water, so with the pressure it got unclogged and sent out the black stuff.
I don't know much about diesels, you know better this engines.


Jose Salgado
ODay 322 1987
DREAM ON

 

[Delezynski]

Jose,

A good friend of mine, now cruising in the South Pacific (now in New Caledonia aboard his Nor'Sea 27) posted a good video on Youtube about shaft alignment and shake of the Yanmar. It's at;
http://youtu.be/hMGN4OnmH0s

Take a look, I think it will help. The vibration changes as the speed changes.

Greg

 

[scorpio77]

I checked the video, I will compare the vibration in my boat, thank you Greg for the info and the help, I will also find out about the mixing elbow, maybe it is clogged with soot and carbon.

Jose Salgado
ODay 322 1987
DREAM ON

 

[scorpio77]

Thanks also Stu for the help in this matter

Jose Salgado
ODay 322 1987
DREAM ON

 

[mikenovit]

My 322 Yanmar has also had sudden loss of RPMs/slower speed.

Hi all folks, Im looking for some experience Yanmar owners, about a month ago I purchased a beautiful ODay 322, with a Yanmar 2GM20F working flawlessly, a couple of days ago while returning from the sea to San Diego Bay, it was late and the wind was not cooperating at all, so I stowed sails an turned on the engine, after motoring for a while at 4-5 knots, the boat lost speed until just 1 knot, I reviewed the engine RPMs, being ok, accelerating and decelerating normally, but apparently the propeller was not getting the power and I heard a noise like if it was skidding, then I looked at the boat sea water discharge and suddenly it started to expel dirty black water for a while, so I shut down the engine, then I checked the oil and coolant, being both at the full marks and with no leakage at all.
So I hoisted sails again and managed to sail to the marina, arriving around 11 in the night.
Before entering the Marina, I started the engine again, hoping to have it available for the docking in the night, It started nicely, I put some thrust in it, getting two knots, so I decided to accelerate it more, and surprisingly it worked ok getting the normal 4-5 knots as if nothing have occurred before, no more black water, no more skidding noises.
The next morning I took it out to the bay briefly just to make a quick revision of the engine and it worked apparently ok.
Has anyone of you folks have an idea of what could happen to the engine, I would appreciate your help to get this matter solved.

Jose Salgado
ODay 322 1987
DREAM ON

My 322 Yanmar has also suddenly lost RPMS/speed for short period, then came back to regular speed and RPMs. No idea why, but if someone can give us a clue it would be appreciated.

Mike Novitsky
O-322 1988
AMAZING GRACE II

 

[Weasel]

Check the exhaust elbow off the engine where the engiine exhaust is mixed with the cooling water. This would cause the black crud and also drop your engine power.
If you have the cast "u" type take it off & check it w/ a flashlite. If plugged get a new one. If you have thr stainless steel 45 degree exhaust connection it can be cleaned, the cast "u" type cannot. Also check your inlet air filter. Sometimes they disolve leaving black residue.

 

[kloudie1]

Probably a problem with the shift cable not pushing the lever on the transmission quite far enough. Next time it does that, go down and very carefully, manually push the gear lever more in the direction it is going.. If that stops the problem then have the cable adjusted .. or lubricated or replaced as necessary..
The noise may have been the clutches slipping so now would be a great time to change the oil in the transmission.. That transmission uses the same oil as in the engine. It takes only 0.25 liter to fill it, about 8.5 fluid ounces

 

[JayTee]

Before you start making adjustments to anything, I thought I would provide some useful input. (You don't want to mess with your alignment if you don't have to!)
I also have a Yanmar 2G and have had to delve into it's workings somewhat. This engine uses a governor to maintain engine speed under varying load. If you set your throttle to provide an engine speed of, say, 2500rpm, and the load on the engine increases, the engine will maintain 2500 rpm! However, the governor will increase fuel to compensate for the increased load, which will become evident with the blacker exhaust you noted (think of a tractor-trailer accelerating from a stop).
In all likelihood, there is absolutely nothing wrong with your engine or it's alignment. I have to agree with those who say it is very likely that you picked up something on your prop, or perhaps you were pushing through some weeds!

 

[scorpio77]

Thank you Weasel, Claude and Jay,
You know I wanted to check the alignment, but thanks for your opinions, I am more inclined with a problem in the exhaust mixing elbow (mine is fitted with the U shape) because before the issue, when throttled up, the engine was working without emitting smoke or any other stuff, that day at sea when I had the loss of power (but not of RPMs) it started to exhaust a really black and dirty water for a minute or less, something like mud really really black, like crude oil or so, besides the slipping noises. Hours later when I turn on the engine again, the exhaust was expelling only clean water.
Mike, did you lost also RPMs? I think we have to start discarding from less to more, I mean, to give a good check of
- Raw water intake and prop
- Mixing elbow
- Water lift muffler
- Transmission cables and oil level

What do you think of this process guys or do I have to take a different course of action?

Before all this I didnt pay much attention to the engine vibration, but after this, I noted that the engine itself was rocking lightly, thats why Greg suggested and provided the shaft vibration interesting video, tomorrow I also will check the engine and shaft vibration, We will appreciate your opinions on this matter.


Tomorrow I will be at my boat and start by checking the easiest parts, I will post if I find something

Thanks

 

[tkanzler]

What comes to my mind is you might have picked up a plastic bag in the prop. As you sailed in it managed to drop off. If the problem does not come back, that was most likely it.

The other option might be a failing drift pin in the transmission to shaft coupling. It that is it, it will come back soon. But you most likely would not get the black soot in the exhaust water.

If the engine speed hasn't changed, and the boat is losing speed, then either there is a mechanical fault (slippage somewhere), or there is junk on or around the prop or somewhere under the boat, like a drogue. Assuming the mechanicals are working properly, thrust is roughly proportional to engine speed, all other things being equal. Power is proportional to engine speed, possibly as the cube of the speed (I'm thinking of the fan laws - have to research props in water to see if it's the same). Since engine speed hasn't changed (an assumption), but boat speed is lost, it has to be one or the other.

Black exhaust suggests the engine is laboring, and if it's governor regulated, that makes the most sense as the fuel injection rate would be increased to maintain engine speed, essentially lugging the engine.

Any chance you were dragging something large under the boat? Lobster pots? Old sails? Garbage bag around the prop?

 

[scorpio77]

Hi guys, I'm back again from the boat, Hi Tkanzler, thanks for the explanation I check the bottom of the hull, Its clean, the prop the keel and the water inlet.
This is what what I did in these two days and I found nothing obvious to cause the issue,
I changed the fuel filter, it had just traces of water, nothing serious and no foreign matter, I reviewed the engine/shaft alignment, it is ok, no disalignment, the muffler is ok just little water, the air filter is nice and clean, the transmision oil is in the full mark and clean, the gear shifter is correctly linked and it is reaching all the way to engage forward and reverse gears.
The only thing left for months end is the U type mixing elbow, time ran fast and I couldnt open it, Anybody know if I have to drain the whole system to remove it.
This elbow makes sense to me after your explanations that being clogged could cause the loss of speed and luckily throw away all the salt and carbon accumulated, after I accelerated the engine and made some switchings from forward to reverse, so I saw that black water (there was no black smoke or any other color) coming out of the exhaust.

Thank you I will let you know if I find the elbow clogged or rusted.