Sudden Onset Black Smoke - Yanmar 4JH-DTE

[Microship]

Hi from S/V Nomadness, currently at anchor off Hope Island... watching eagles diving for fish off the stern.

I have read the recent black-smoke thread, and the one to which that pointed. Lots of good information there. Still a question remains...

A month ago I ran 3 hours at my usual 2600 RPM or so, and all went well. This weekend I took off for a short trip, and immediately noticed that black gunk was being injected into the water (granular appearance) along with black smoke at anything over about 1800 RPM.

I have been unable to dive on the prop (COLD) to see if there is a line or other fouling. I cleaned the simple mesh air filter on the input side of the turbo, and it was quite oily (there is a hose from the valve cover that presumably slurps up vapors). Aspiration to the engine room has not changed. Injectors were patterned about 50 hours ago. No change in exhaust sound, oil and coolant levels normal, same fuel.

There is some black powdery patterning around the mechanical shaft seal suggesting a little bit of friction, but I have a hard time imagining that it would represent a significant load. The only recent service since the last run was a Max-Prop nose-zinc replacement by a diver, and I can't imagine anything he could have done to cause an increase in loading.

I'll be heading back to home port tomorrow (hopefully mostly under sail), and would love to know if any of this suggests a serious problem brewing... or if I should just take it slow until I can get someone to take a look...

Thanks and happy 4th!
Steve

[Badsanta]

If it runs at speed in neutral with no problem and smokes in gear, I would check the prop.

[Evan]

I think Mr Santa means "if it runs at full redline speed in neutral". And I agree it's probably the prop. Is your prop the "vary the pitch underwater type?" Maybe your diver messed with the pitch by accident when changing the zinc.

[Microship]

Wow, interesting... I didn't know that was possible. OK, we'll investigate the Max-Prop... thanks!

[Boracay]

How old is the engine?

How old is the air filter?

[Badsanta]

depends on the max prop for the adjustment. But if he just replaced the zinc something could have easily got stuck under the prop blades and caused it to not fully return to normal. My max prop has to be removed to adjust it. The newer ones have a dial on the shaft. But a barnacle or rope or well anything can get stuck in there and stop it from returning to original settings. It does not take much growth to really mess mine up.

[Microship]

Engine is 1987, and has 3092 hours. The air filter came with the boat, and is not the paper kind I would have expected... just a fine-mesh screen cylinder mounted to a coarse frame with larger holes. It is quite dirty with oil, and I cleaned it somewhat casually with a paper towel... before heading back to port tomorrow I'll do it more thoroughly with detergent. This is new since previous run, though, so I don't think that's it.

Getting time for bottom paint anyway... maybe it's getting to be haulout time for a close look at the prop.

Steve

[Microship]

Mmm, been reading more about this on various fora and blogs. I'm still not sure how a nose-zinc installation (it had completely dissolved) could screw up pitch, but it is clear that an error here could easily cause the sudden appearance of black smoke that worsens at higher RPM. Thanks for the help, guys. I'll sked a haulout and have a word with the budget diver. And call PYI, while I'm at it.

[Boracay]

Do you have any way of checking your compression?

[Microship]

Originally Posted by Boracay

Do you have any way of checking your compression?

Not here at anchor, alas. Guess I'm going to have to get beyond my habitual strategy of tiptoeing around engines, digging in with reluctance only when a problem exists. Poring over Calder and Compton is instructive, and I realize how little I know about these things.

Still, the biggest clue is the abrupt change. The only intervening event is that zinc change, so while it seems a long shot, it is suspicious. It could also be fouling, of course.

Dreaming of clean, geeky electric propulsion systems...
Steve

[Dockhead]

Do make sure that you tell us what it was, when you figure it out. These trouble shooting threads are either (a) fascinating and useful for all of the rest of us; or (b) utterly useless, depending on whether or not we get to hear the rest of the story.

[markpj23]

Originally Posted by Microship

Engine is 1987, and has 3092 hours. The air filter came with the boat, and is not the paper kind I would have expected... just a fine-mesh screen cylinder mounted to a coarse frame with larger holes. ...
Steve

I too was surprised to find the intake air "filter" on my previous boat's 4JH2-DTE was only the screen you describe. It's the factory unit believe it or not... and cleaning is just as you describe.

As for the black smoke... KISS ..... last item touched was the prop. You're heavily loading the engine. Be sure to let us know once the mystery has been solved.

[Microship]

Will do! Alas, no wind today, and many miles back to the stable... I'll tiptoe and keep the revs low, then sked a haulout. I'll be back with results.

Cheers and thanks,
Steve

[Badsanta]

The thinnest part of the max prop zinc is the bolt holes. They will dissolve and then drop off the whole zinc. The best thing I was told is to paint on the zinc a 3/4 inch stripe on the outside of the three bolt holes that you use. That will force the zinc to be used on the biggest part and not the thin edge. I found that my zinc would fall off after little use. I have since added a shaft zinc, just in case as I dont want to damage the 3K prop. PYI has a great web site.

[Badsanta]

You could have just simply picked up some fishing line around the prop.
Best of luck