Yanmar blowing black, then eventually stopped

[Jimmy_G]

Thanks Compass 790.
I didn't notice a hole burned in the plastic waterlock muffler, but will have another look for signs of that. I always check that water is exiting the exhaust', and it was on the day that I stalled, although I didn't notice whether it was or not just before the engine stopped.
Just to ensure I'm getting it right, cleaning the 'injection point' basically means punching through the hole (currently covered in carbon build up) where the injection point joins the elbow. Hopefully that's a foolproof task.
So if I clean the elbow & water injection point and she runs well, can I assume that I've resolved the issue for now?
Although I also see the value of trying to clear the carbon from inside the manifold, and your description seems very do-able. So I might then take that on while I'm at it. She is seawater cooled, but I guess that it doesn't matter whether I use fresh or seawater for this job......
I will report back. Thanks again!
Dave

[Compass790]

Originally Posted by Jimmy_G

Thanks Compass 790.
I didn't notice a hole burned in the plastic waterlock muffler, but will have another look for signs of that. I always check that water is exiting the exhaust', and it was on the day that I stalled, although I didn't notice whether it was or not just before the engine stopped.
Just to ensure I'm getting it right, cleaning the 'injection point' basically means punching through the hole (currently covered in carbon build up) where the injection point joins the elbow. Hopefully that's a foolproof task.
So if I clean the elbow & water injection point and she runs well, can I assume that I've resolved the issue for now?
Although I also see the value of trying to clear the carbon from inside the manifold, and your description seems very do-able. So I might then take that on while I'm at it. She is seawater cooled, but I guess that it doesn't matter whether I use fresh or seawater for this job......
I will report back. Thanks again!
Dave

Yes punch thru but I'd google cleaning carbon off or look on youtube for tricks & clean elbow best as possible.
DONT spray seawater in air intake, must be fresh.
Yes I'd say if it runs well you will have resolved the issue for now but you didn't say if your overheat alarm is working????
Also make sure oil pressure alarm working.

[Jimmy_G]

Thanks again.
I believe my alarms are working, but will check again on startup.
Freshwater it is!
cheers.

[Jimmy_G]

Turns out I diagnosed the problem incorrectly. the cooling water does not exit directly into the exhaust elbow cavity, but into a sleeve on the inside of the elbow. And has a raised section where it enters the elbow which gave me the impression it was carbonised over (Pic attached).

And as you can also hopefully see, the elbow is pretty clear. So I'm a little stumped again......

The manifold has some blockage as I mentioned (maybe up to 50%), but I'm not sure that would bring me to a halt as it did.....

To quickly recount, she blew a lot of black smoke and carbon drops when over 1800 revs, then stopped on me after 4 h motoring at 1500 rmp (while no smoke blowing).
Exhaust elbow entry1 (after breakdown_Aug2019).jpg Views: 179 Size: 415.2 KB ID: 199076" style="margin: 2px" />


And thoughts?

[model 10]

Wow, if everything above is not the answer, you are getting into stuck valve etc, or fuel pump territory.

[Compass790]

I would have thought the inner pipe in yr btm pic should be central to the bore but not being a 2gm20 owner maybe one of them can comment. It's not broken inside is it?
Looking at the top pic the carbon buildup at that flange end doesn't look that bad, certainly not able to stop engine on its own.
I'd be suspecting injector or fuel delivery problems now but wait till someone comments on your exhaust pics that has a 2gm20

[Compass790]

Yes inner pipe is meant to be concentric.
https://www.pbo.co.uk/expert-advice/...he-elbow-24029
According to their pic of a new one.
hope that helps.
I'd buy or make a stainless one if I was you. Make out of sched 10 316L pipe rather than tube & it will last for ages

[Wotname]

Originally Posted by Jimmy_G

Turns out I diagnosed the problem incorrectly. the cooling water does not exit directly into the exhaust elbow cavity, but into a sleeve on the inside of the elbow. And has a raised section where it enters the elbow which gave me the impression it was carbonised over (Pic attached).

And as you can also hopefully see, the elbow is pretty clear. So I'm a little stumped again......

The manifold has some blockage as I mentioned (maybe up to 50%), but I'm not sure that would bring me to a halt as it did.....

To quickly recount, she blew a lot of black smoke and carbon drops when over 1800 revs, then stopped on me after 4 h motoring at 1500 rmp (while no smoke blowing).
Attachment 199076

Attachment 199077
And thoughts?

My 2GM20 had the same exhaust mixing pipe except the inner tube was more centred - not perfectly but better than the one in the picture. Double check to see if all is clear in there.

When you say 50% blocked, are you talking area or diameter? While neither is good, 50% diameter would give similar symptoms to yours.

Will the engine run up to max revs (3600) at WOT in neutral?

I agree with the others, it's is becoming less likely to be an exhaust blockage but any blockage should be removed before looking further.

[Wotname]

Originally Posted by Jimmy_G

........

She is a Hartley sister twin keel, plywood boat; and I cannot easily redline the engine in neutral due to a press-in button that switches between neutral and not in the way of the accelerator lever. I think we reached about 2800 revs when testing after a clean and prop replacement.

Will repost what happens next.
Thanks again.
(any updated views still welcome

OK, I forget you have difficulty with a WOT at neutral but you can easily disconnect the throttle cable at the injector pump to perform this test. Disconnect the cable and manually operate the lever on the injector pump.

Also, 2800 at WOT with clean bottom and prop indicates you are over propped and thus any fouling on the prop will quickly affect engine performance. You should be able to reach max rpm with a clean bottom and prop in calm water.

This may not be your initial problem but will make diagnostics harder.

[Jimmy_G]

Thank you all,
The exhaust pipe is pretty central. I have just not taken the pic square on.
I am unable to run the revs high in neutral because the button that toggles between in and out of gear hinders the throttle lever.
50% blocked referred to the diameter of the exit holes that I could see when gazing into the manifold. You may be able to see it in the new pic.
BTW, what is WOT?
Dave

[Jimmy_G]

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

[Wotname]

Originally Posted by Jimmy_G

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

No
WOT = wide open throttle

[Wotname]

Originally Posted by Jimmy_G

....
50% blocked referred to the diameter of the exit holes that I could see when gazing into the manifold. You may be able to see it in the new pic.
........
Dave

Wow that's looks very blocked to me but perhaps it is the photo!

Me, I would want to remove the carbon but I'm not a diesel expert - however this can't be helping.

[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

[Wotname]

FWIW, a 50% reduction in diameter reduces the area by 75% (if my maths serves me correctly). That is going to create a lot of back pressure effectively preventing the engine from breathing i.e. the same as any restriction in the air intake.

Reduced air intake but with the same fuel input will cause black smoke and reduced power output - pretty much your symptoms.

BTW, the injector pump and governor will keep dumping in fuel trying to get to the power setting you have selected with the throttle while the air is intake is determined purely by the engine design and the exhaust back pressure - so any large increase in exhaust back pressure effectively causes over fuelling.

Again, you might get better professional advice, I'm just a DIYer whose has had several older small boat diesels