Yanmar blowing black, then eventually stopped

[Wotname]

Originally Posted by Jimmy_G

Agreed.
Anyone think this (reduced bore size in manifold) would be the problem?
One suggestion has been to spray water mist into the air intake when running at temperature and at 1500rmp. With the resultant steam blowing carbon out.
Is this my way forward?
d

I would (cautiously) try it. Done carefully (i.e. mist only) it shouldn't hurt anything IMO.

These engines are pretty robust - just don't dump a load of water into the air intake.

But it's your call

[Compass790]

Originally Posted by Jimmy_G

Agreed.
Anyone think this (reduced bore size in manifold) would be the problem?
One suggestion has been to spray water mist into the air intake when running at temperature and at 1500rmp. With the resultant steam blowing carbon out.
Is this my way forward?
d

I'd try it Jimmy G but trouble is it doesn't address the problem of why the engine stopped. It's an easy thing to try. The carbon buildup is not good & best removed as others say but I doubt it made the engine stop. Did the symptoms you describe only start immediately after the service or were slowly getting worse over time?
Blocked exhaust was the most likely reason, our exhaust was worse though & it still ran, but badly. Certainly makes it blow more black smoke having exhaust restriction.
I would check the injectors are spraying properly & compression as well now. Trouble shooting consists of eliminating the possibilities. I'm starting to doubt exhaust was the only problem. It's often the way that you can have multiple faults contributing to the engines problem on an older engine.
Normally it's a fuel problem if the engine just dies
If you want to work on it yourself I'd recommend a good book like " Trouble shooting marine diesels " by Peter Compton. ( not sure if I got the title right but author is I think)

[Wotname]

JimmyG, I'm not clear after re-reading this thread but is the engine starting currently or not or haven't you tried it again???

I'm wondering if there isn't some other exhaust constriction and I would try starting it with the exhaust mixing point off the engine. I wouldn't run it this way but a short start and run for a few seconds could be useful to know.

[Compass790]

Originally Posted by Wotname

JimmyG, I'm not clear after re-reading this thread but is the engine starting currently or not or haven't you tried it again???

I'm wondering if there isn't some other exhaust constriction and I would try starting it with the exhaust mixing point off the engine. I wouldn't run it this way but a short start and run for a few seconds could be useful to know.

Yep good idea to try this as well.

[Compass790]

You can run it for a minute easy if you can stand the fumes & the mess inside. If it's still blowing carbon when you rev it it will go everywhere.
But Wotname is on the ball, you need to find out if the exhaust is restricted downstream

[Jimmy_G]

To update and recap, I took off the mixing elbow and noted it was quite clear and open. But noted some carbon build up inside the engine block where I could see in when the mixing elbow was removed.
I also filled my fuel tank (which was below 20 l or 25% full) given that the symptoms of my recent breakdown may have been related to fuel blockage, reset the fuel system (with a deisel mechanic) and she started and ran well. In a similar way to she had been recently.
So I think I'm back to square 1. Running fine below 1800 rpm, but blowing lots of black smoke and carbon droplets above 1800 rpm (when in gear). This was done while tied to the pontoon.
So I seem to think my next likely options are to check that the exhaust piping system after the mixing elbow is not blocked, then start looking at injectors.
I am also thinking about adding some fuel/injector conditioning product to look for a miraculous solution that way.
Any thoughts?
Slightly stumped again.
Dave

[Wotname]

Originally Posted by Jimmy_G

To update and recap, I took off the mixing elbow and noted it was quite clear and open. But noted some carbon build up inside the engine block where I could see in when the mixing elbow was removed.
……………..
So I think I'm back to square 1. Running fine below 1800 rpm, but blowing lots of black smoke and carbon droplets above 1800 rpm (when in gear). This was done while tied to the pontoon.
So I seem to think my next likely options are to check that the exhaust piping system after the mixing elbow is not blocked, then start looking at injectors.
I am also thinking about adding some fuel/injector conditioning product to look for a miraculous solution that way.
Any thoughts?
Slightly stumped again.
Dave

Well the good news is you are back at square one so let’’s get to the real reasons of why it won’t power up over 1800 loaded.

Question: have you removed any decent amount of the carbon noted inside the head? I’m unsure from you above posts whether you have attempted this or not.

If not, please do the best you can to remove as much as possible. Not removing it makes further diagnostics difficult.

Too much exhaust restriction will lead to black smoke and low rpm in gear.

Next, please note that any fouling on an over propped boat will lead to low rpm and black smoke at WOT. This is exacerbated if you are stationary (tied to the dock).

From what you have previously posted, it is likely you are over propped so unless the water is freezing, get over board and remove all the critters on the prop. Then try the boat under way in calm water.

Check the tappets (valve lash). It is quick and easy to do so it is one thing that can be eliminated without much effort.

Previously you posted

Originally Posted by Jimmy_G

So I should see whether I blow black smoke etc when >2800 revs in neutral?

to which I answered “no”. I misunderstood your question and thought you were asking if you should expect black smoke at >2800 in neutral.
Please allow to correct my error.
Yes, you should try running the engine at WOT in neutral and it should run up to 3600 without any smoke. The governor will stop the engine from exceeding 3600.

This is an important diagnostic step and again is easy to do even if you do have to disconnect the throttle cable at the injector pump.

If all of the above fails to resolve the problem, then and only then look at the injectors. While it possible they are faulty, they might difficult to remove, especially if they haven’t been removed for some years - if ever!

The reason I suggest all the other avenues first is that all of them are known to cause your symptoms and are common faults. They are also relativity easy to eliminate. The injectors are less likely to be the issue and could well be time consuming to remove. They can checked by yourself if you are willing to give it a go. Plenty of help here on CF if you do want to DIY.

IMO, you will sort this problem by doing all the above in order and without spending too much money (but you will spend some sweat)!

Good luck

Below are a few extracts from this thread that leads me to give the above advice.

Originally Posted by Jimmy_G

I….. The hull is quite clean but the prop it accumulating a few crusty critters………
………..

Originally Posted by Jimmy_G

…..
The tappets were not serviced last time ……
…….think we reached about 2800 revs when testing after a clean and prop replacement.

Originally Posted by bouton

I had similar symptoms on my Farymann. Black smoke on revs 2000. If I put throttle for more revs. With load. Without load I reach 3500 revs and no black smoke. I found out that My sailboat was overpropped. When I put smaller prop engine works ok with max 3200 rev and without black smoke. Can you confirm, that without load there is no black smoke?

[Jimmy_G]

Thanks Wotname for that comprehensive assessment.
I had prop advice from a local but experienced expert so I am hoping that I'm NOT overpropped, but its possible.
I know there is some prop fouling of small hard-bodied critters (1 or 2 mm across). But not sure how bad this is in context with this issue.
I can run her in neutral to max revs and see what she does. I haven't seen her before at anything like those revs, but will do so tomorrow.
I will also try and remove any carbonisation from the engine block at the point of the exhaust elbow join. As much as I can get to anyway. Not sure how to do this, and am a bit concerned that I will knock chunck back into the engine block. Hopefully this is not an issue.
I will report back.....
Thanks again,
Dave

[Wotname]

Originally Posted by Jimmy_G

Thanks Wotname for that comprehensive assessment.
I had prop advice from a local but experienced expert so I am hoping that I'm NOT overpropped, but its possible.

Another possibility is that you are correctly propped but the engine isn't making enough power (low compression - faulty injectors etc). Let's hope this isn't the case.

FWIW, you should be able to achieve max RPM at WOT with a clean bottom and hull if correctly propped. For a 2GM20, max continuous rpm is 3400 and max intermittent rpm is 3600.

I know there is some prop fouling of small hard-bodied critters (1 or 2 mm across). But not sure how bad this is in context with this issue.

No good if on the blades but sort of OK if only of the hub. But if you can get rid of them, it is one less thing to consider.


I can run her in neutral to max revs and see what she does. I haven't seen her before at anything like those revs, but will do so tomorrow.
I will also try and remove any carbonisation from the engine block at the point of the exhaust elbow join. As much as I can get to anyway. Not sure how to do this, and am a bit concerned that I will knock chunck back into the engine block. Hopefully this is not an issue.
I will report back.....
Thanks again,
Dave

I'm no expert but I would take the rocker cover off, rotate the engine with the hand crank until both exhaust valves are closed as much as possible and then chip away at the visible carbon while holding a vacuum cleaner hose at the exhaust port.

Then before starting, spin the engine over decompressed for 5 or 10 seconds using the starter motor - this should blow out any remnants that might have made it into the cylinders.

Maybe others will have better ideas.

Good time to check the valve clearance before refitting the rocker cover. The correct clearance is 0.008" or 0.2mm.

BTW, does the engine start easily when cold? Like within a second or two at the most. Easy cold starting indicates good compression.

[Trawlerman]

All focus has been on the carbon buildup, however I suspect that the carbon is just the indication of the issue, not the problem per se. This excess carbon is indicative of the engine running too rich. This can be from several reasons. The classical one is that the boat is over-propped and the amount of power absorbed by the prop at a given RPM is not consistent with the engine/prop intended design. It is important to remember that in the setting of the fuel-per-injection stroke of the pump is related intimately with the RPM. That is to say that at a given "throttle" (misnomer) stetting, you are really "commanding" a certain RPM, and the fuel injection pump will commence to "squirt" progressively more fuel till that RPM is reached. The engine designer intends that there is sufficient air in the cylinder available to burn the amount of fuel necessary to get the engine up to that "commanded RPM". Of course in no-load (WOT) this does not demand much per cylinder-stroke fuel quantity, but the designer knows what the acceptable load is that will not demand more fuel than there is air to burn it. HOWEVER, If the engine has been running for some time overloaded, there will be carbon buildup in the cylinder head reducing air volume, and in the intake valve open-valve area (restriction) thus reducing the air density (less O2) thereby causing an ever increasingly too-rich mixture thus creating more carbon. That alone could be the cause of your problem, and it is insidious since it is a slow cumulative problem that finally "breaks the camel's back". The water attempt at decarbonization is potentially valuable as a diagnostic, but also check the prop pitch against the original design. If it is a bit to much bite this may have been a problem that took time to build up to, but was inevitable.

[blinchy]

Hi Guy's

We had a 2GM20 in a Legend 326 which had the same issues, after months and months of diagnostic works we eventually solved the issue.

We took a lot of advice and most diesel engineers said that the black smoke issue was from overloading, i.e over propped on a boat.

We dismissed this as the yacht was 5 years old and the black smoke manifested itself over a 2 - 3 week period.

We carried out the usual checks plus the following diagnostics;

1, Made sure exhaust system was clear and free flowing
2, Had injectors tested and cleaned
3, Borrowed an injection pump and tried that on our engine
4, Adjusted the injection pump rack

Eventually we took off the cylinder head to have a good look inside the engine, the diagnosis, polished bores.

The cylinder bores were highly polished with no visible honing cross hatch, we honed the bores and replaced the piston rings thinking that we had finally cured the problem.

Though the black smoke had reduced significantly, if you looked hard it was still there and still soot in the water.

So we went back to the original diagnosis of over propped.

Our unit was a sail drive with the square ended aluminium prop which can't easily be re-pitched so we had half an inch off the diameter.

Problem solved, no more soot or smoke.

Looking back at our experience;
The exhaust output from our engine was always a little dirty even though it wasn't seen as an issue
Operating the engine overloaded for many years and also whilst trying to rectify the problem caused the excess un-burnt diesel to wash the lubricating oil from the cylinder honing, this led to polishing of the bores.
This reduced the power output from the engine which made the boat even more over propped.
Even if we had changed the propeller to a small pitch / diameter as first suggested, the damage, in our case, was already done.

I hope your issue is simpler and less expensive to rectify but in our experience black smoke / soot from a diesel is an overloading issue.

As a post script,
Despite our earlier experience with the 2GM20
We got to know these great little engines very well and bought a overheated unit and had that re-bored.
We run it as a generator on our current boat, it has a very large alternator attached to the output shaft.
If the alternator kicks in before the engine is up to speed we make smoke, lots of black smoke where it is overloaded!

[Compass790]

Originally Posted by Jimmy_G

Thanks Wotname for that comprehensive assessment.
I had prop advice from a local but experienced expert so I am hoping that I'm NOT overpropped, but its possible.
I know there is some prop fouling of small hard-bodied critters (1 or 2 mm across). But not sure how bad this is in context with this issue.
I can run her in neutral to max revs and see what she does. I haven't seen her before at anything like those revs, but will do so tomorrow.
I will also try and remove any carbonisation from the engine block at the point of the exhaust elbow join. As much as I can get to anyway. Not sure how to do this, and am a bit concerned that I will knock chunck back into the engine block. Hopefully this is not an issue.
I will report back.....
Thanks again,
Dave

Lotta good advice for you to work at Dave, Very good posts from Wotname.
Do you know what your props pitch & diameter is? You can check on vicprop calculator ( google it ) was in the ballpark for our boat.
Dont know if it caters for bilge keeler but worth a look

[tbjhealy]

2GM20 Owner here. Had the same problem this year. Did everything mentioned in the thread. Finally pulled the boat. Picture says it all. Some weird, fast growing things growing in New York Harbor this year. Zinc Anode completely gone. Cleaned it up. Good, solid power under way. NO BLACK SMOKE. PHEW! Hope your journey ends on the same note. Good luck.

[Jimthebuilder]

Originally Posted by Jimmy_G

I had my Yanmar 2GM20 serviced a few months ago and then found it blowing black smoke and carbon spots on the water (not oil) when over 1800 rpm. It seemed to run fine below those revs. The hull is quite clean but the prop it accumulating a few crusty critters.
I noted that the mechanic overfilled the sump so I got him back to bring it back to full. that made no difference to the smoking above 1800.
My mechanic suggested removing the air filter in case it was air blockage via the intake, but that didn't change it.'My next move was to look at the air exit for a narrow or mostly blocked exit, but I haven''t done that yet.
Yesterday we went out, but after about 4 h running of the engine it lost revs then died after a few minutes.
Blowing out the carbon accumulation was an early suggestion, but there was too much black smoke for that scenario and running it harder didnt make things any better. So I have all but ruled that out.
I have had injectors suggested, but not much else to go by.
I am not aware of the engines history other than it was installed in 1990 and underwent some sort of rebuild about 8 years ago.
I am about to try and find a good quality marine diesel mechanic in the Brisbane area (SE Queensland) (any suggestions?), but was looking for any expert advice that may be out there.
I recently read a long blog (~27 pp) on this channel about a guy on holidays
with a similar problem and don't want to go through the semi-blind, 'lets try this' style of approach to finding the problem, which eventually ended in him having to buy ad install a new engine, plus costs of all the experimentational, but unsuccessful attempts at diagnosis and work ($25K).
Ideas welcome.

regards,
Dave

Hi Dave
I’ve used ‘Wave Break Marina’ at Redlands for my 3YM30 and found him very helpful. Steered me away from genuine wet exhaust elbow replacement at half the price$640 to $380). Hes also mobile if that helps.

[Bob328]

Check exhaust hose from exhaust elbow to muffler. If it has delaminates from poor water flow, it will block exhaust. It will also cause your mid- range problem with carbon blowing into water from exhaust. It can cause all the symptoms you are describing. Had same problem with my boat a few years ago. Inner lining of exhaust hose delaminates from hot exhaust. I have been a marine diesel mechanic for 30 years.