Yanmar blowing black, then eventually stopped

[Wotname]

Originally Posted by 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!

Great first post Blinchy!

And worth waiting for . Looking forward to more

[Wotname]

Originally Posted by Jimmy_G

.....I think we reached about 2800 revs when testing after a clean and prop replacement.
.........

This may be a red herring and not important but why was the prop replaced. It may be part of the reasons you have problems today.

I'm thinking like others here that your current symptoms have been a long time in the making and you have too both find out why you are currently over fuelling (black smoke, restricted rpm) and why the carbon build up has occurred in the first place - perhaps gong back years.

I recall you believe the engine was "overhauled" eight years back, perhaps the real problems have never been addressed.

You wouldn't be the first "new" owner to discover old problems that previous owners either ignored or just papered over through ignorance.

Let me repeat though - this is fixable and usually take more time and sweat than money.

[Wotname]

Originally Posted by 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.

This is great explanation and should be read by all small boat diesel owners, many forget the small marine diesel is quite different from a petrol (gas) engine when it comes to fuel /air induction.

I'd like to repeat this section "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"".

Originally Posted by 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.

Another very good suggestion.

[StoneCrab]

Originally Posted by Compass790

Blocked exhaust elbow is most likely cause if boat bottom & prop clean clean.
When it was serviced were the tappets done?
Compression check?
Usually blowing black smoke is overloading, too much back pressure, insufficient compression, air intake restriction or faulty injectors.
thats a few things for you to start on.

This advice is spot on. Black soot from a diesel is incomplete combustion of either diesel fuel or oil.

If this starts after servicing an engine, this is usually caused by something that the mechanic did or didn't do that caused an intake blockage. If it develops over time, it could be intake blockage or oil getting into the cylinders.

Are you consuming oil?

I had a truck that developed the smoking problem months after service. It wasn't using oil. I called another mechanic who didn't have time to schedule me in so he told me to stick my entire arm through the intake tube until I could feel the screen on top of the manifold. He said that I would most likely find all or part of an air filter gasket lying on top of the screen. I did this while we were talking. He was correct. It just took that long to make its way to the screen from the filter. The engine would run at low rpm's and blow black smoke under load.

If your injectors aren't set properly and blowing too much fuel into the cylinders, this can also cause the problem. This can be checked at a shop on the bench. They are set to a relief pressure which is adjustable.

The injectors also need to be atomizing the fuel when it is released into the cylinder. This is why some injectors have a needle sticking out of the center of the nozzle. Are any of these damaged? If it is just squirting in a stream of fuel, the combustion will not be complete, but I also wouldn't be surprised if the engine wouldn't start.

The "rack" in the injection pump also adjusts the amount of fuel injected when you vary the throttle. It adjusts the length of the pump stroke for each cylinder. These should be closely calibrated so that you aren't dumping more fuel in one cylinder than the others.

The oil rings on the pistons could have also failed causing oil consumption and smoke. If the compression rings are all good, a compression check may or may not reveal anything. A look into the cylinders with a bore-scope would tell you if the cylinders are scored up.

Is your gearbox or transmission excessively hot? Although I suspect that you'd hear something first, if something is broken and bound up, it could be putting an unusual load on the engine.

[Shaneesprit]

Take the boat out and give it near full power, for 1 - 3 hours, Carbon comes from you idling around at low revs / power, when you go above this the engine and exhaust get up to working temperature and burn off the carbon hence the deposits

[Mainebristol]

I have a 2gmf. Love it. My max rpm in gear at speed is about 3,100 rpm. I feel I am slightly overpropped, but not by much. If you can only manage 2,800 rpm, then I think you are clearly overpropped.
The only real trouble I had with this little engine was when I ignored the primary fuel filter for a few years. That just brought us to a halt, though. Never had any real trouble with black smoke, but I did have to replace the exhaust elbow last year when it started rusting through. The elbow is best thought of as a consumable, just like the filters. It has to be replaced now and again, really for the sake of the head.

[Shaneesprit]

There is a lot of absolute rubbish written here by people who have heard rumours and tricks, all A load of crap.

1) it is not possible to overload a Diesel engine with a prop - NOT possible!
2) spraying water into the inlet - BAD Idea
3) Carbon is caused by low load and low cylinder temperature not by excess fuel
4) leaking injectors cause Oil dilution with Diesel
5) Carbon in the exhaust causes lack of power due to exhaust back pressure
6) Not being quite able to reach full Engine Speed is a good thing, obviously closer you can get to max RPM the better but reaching MAX RPM to early is bad

I will try and answer your questions if I have time - I didn’t look at your pics
Is she still running?

[Compass790]

[QUOTE=Shaneesprit;2972149]There is a lot of absolute rubbish written here by people who have heard rumours and tricks, all A load of crap.

1) it is not possible to overload a Diesel engine with a prop - NOT possible!

This statement 1) is the biggest piece of crap I've seen in the thread to this point.

[Wotname]

Originally Posted by Shaneesprit

There is a lot of absolute rubbish written here by people who have heard rumours and tricks, all A load of crap.

1) it is not possible to overload a Diesel engine with a prop - NOT possible!..............

Err... What!
Of course it possible to overload a diesel with an incorrectly sized prop. Please think about this if you don't believe it as it is unhelpful to knowingly post incorrect information.

If you can't work it out, I happy to debate the subject on a new thread but I have no wish to de-rail Jimmy_G's thread ATM; at least until he resolves his engine problem.

[Jimmy_G]

Thanks again folks,
Prop photos (and hull) from one year ago.....
I have filled the fuel tank, replaced 1st stage filter, and she started great.
After warm up I got my black smoke at 1800 rmp (while tied to the pontoon).
My next moves were to jump in with a tank and clean the prop to look for a difference, then replace the hose and muffler system from the mixing elbow back; and add an additive to the fuel to potentially help injector performance.

Hopefully one of these will bring me joy, other wise I'll continue to dig deeper.

Dave

[skipperpete]

Originally Posted by Shaneesprit

There is a lot of absolute rubbish written here by people who have heard rumours and tricks, all A load of crap.

1) it is not possible to overload a Diesel engine with a prop - NOT possible!
2) spraying water into the inlet - BAD Idea
3) Carbon is caused by low load and low cylinder temperature not by excess fuel
4) leaking injectors cause Oil dilution with Diesel
5) Carbon in the exhaust causes lack of power due to exhaust back pressure
6) Not being quite able to reach full Engine Speed is a good thing, obviously closer you can get to max RPM the better but reaching MAX RPM to early is bad

I will try and answer your questions if I have time - I didn’t look at your pics
Is she still running?

1.
It is possible to overload an engine with a propeller simply by running the engine at full throttle while strapped to the dock and note the black smoke, low rpm achieved and rise in jacket water temperature.
2.
spraying water into engines is a thing. Google "Turbo wash". Engineers do this from time to time to clean the compressor side of turbo but not always into the engine itself.
3.
Carbon is caused by excess fuel to air ratio among other things too numerous to mention and presents as exhaust soot and coking.
4.
Leaking injectors can cause lube oil dilution on engines where the injectors are under the valve cover. GM, Ford lehman , a recent Yanmar 4JH series and the Lombardini's in the little Paguro generators but the type of leaking is rarely spray nozzle leaks, it is usually pipe connection leaks that allow fuel oil to directly drip into the sump.
5.
Agreed. In fact anything that increases exhaust back pressure will cause lack of power hence Yanmar's insistence on 75mm and larger for relatively small engines.
6
And agreed on this too, most installation literature gives the rpm under maximum load but it's not easy to get a good match unless you have a adjustable pitch propeller.
Cheers, Pete.

[Wotname]

Originally Posted by Jimmy_G

Thanks again folks,
Prop photos (and hull) from one year ago.....
I have filled the fuel tank, replaced 1st stage filter, and she started great.
After warm up I got my black smoke at 1800 rmp (while tied to the pontoon).
My next moves were to jump in with a tank and clean the prop to look for a difference, then replace the hose and muffler system from the mixing elbow back; and add an additive to the fuel to potentially help injector performance.

Hopefully one of these will bring me joy, other wise I'll continue to dig deeper.

Dave

A reasonable plan IMO.
If at possible, next time can you do a run the engine underway (i.e. not tied to the dock). The difference in the rpm between the two (at WOT) will help determine how suitable your prop size is.

[Wotname]

Originally Posted by Jimmy_G

Thanks again folks,
Prop photos (and hull) from one year ago.....
I have filled the fuel tank, replaced 1st stage filter, and she started great.
After warm up I got my black smoke at 1800 rmp (while tied to the pontoon).
My next moves were to jump in with a tank and clean the prop to look for a difference, then replace the hose and muffler system from the mixing elbow back; and add an additive to the fuel to potentially help injector performance.

Hopefully one of these will bring me joy, other wise I'll continue to dig deeper.

Dave

Re the photos, presumably the first one is of the old prop. If so, I can see why it was changed -it's shocker IMO!

[Wotname]

Jimmy_G, you may also want to read post #10 in this thread
http://www.cruisersforum.com/forums/...er-223042.html
It describes a fairly simple DIY method of determining exhaust back pressure. This will give a good idea of the health of the exhaust system downstream of the mixing point.

[Jimmy_G]

Originally Posted by Wotname

Jimmy_G, you may also want to read post #10 in this thread
http://www.cruisersforum.com/forums/...er-223042.html
It describes a fairly simple DIY method of determining exhaust back pressure. This will give a good idea of the health of the exhaust system downstream of the mixing point.

Hi again,
I just looked at #10 and it just said replace the mixing elbow??
Seems to be the wrong post.......