Ford Lehman: Black Exhaust Smoke Stain on Hull

[Geoff H.]

There is only one thing for which I can really fault my 1980 Ford Lehman 120, and I would love to correct this: After an extensive run there's quite a pronounced black stain on my hull just aft of the exhaust exit. The motor runs great, starts great, is stingy on fuel.
Smoke stain (I don't really notice smoke much) seems worse since I switched back to regular oil (can't get synthetic oil where I am) and wonder if this is related.
Also, I replaced the old corroded exhaust manifold with a new one, which seems to have a lot more air induction in its design -- could this be a factor?

Anyone?

[Geoff H.]

And one other thought: I tend to run motor at 1800 rpm. Is this too low for this motor, is that a factor in the smoke?

[TassieBloke]

Hi Geoff,

I have a Lehman 135 in my yacht which I have just taken possesion of. FWIW, the PO of my boat used to run it at 1500rpm during their circumnavigation. It also has a darker area around the exhaust, but nothing too remarkable.

Just a few thoughts, black smoke can mean overworking, maybe you are overproped? What are the exhaust manifold temps like?
Another cause could be a dirty airfilter, however you mention that since the new manifold was fitted, there appears to be greater air flow, which would mean that it should run leaner, thus actually less smoke.
Maybe at the higher rpm's the injectors are overfueling, run at lower rpm's and see how it looks.

Bob over at American Diesel American Diesel Corporation is the undisputed guru of anything Lehman. Give him a holler, and he will surely help. The dude is a legend from Ford Lehman

Let us know how you go, I am also on a learning curve with these motors. From what I can gather, they are bulletproof and so simple to work on.

Cheers,

Bloke

[Geoff H.]

Thanks very much for the thoughts. Yes, I will contact Bob. I've done so quite a few times. I buy all my parts from them, including the new manifold. I don't believe that 1800 rpm is considered running hard, but I'll ask him as well. I had this engine on a smaller trawler 20+ years ago and we ran that at 2000 rpm all the time. The prop is the same prop I've always had, and its true and clean.
The smoke stain seems to have developed more of late, perhaps since the manifold, and also since I switched back to regular oil, so I'm thinking that might be an area worth getting into.
What about engine timing? Any relationship there? (Though she runs awfully good for her to be out of time. Hmm)

[Redcoat]

If you have a flush fitting throughhole I took a piece of PVC and used some 5200 and stuck it up in the exhaust outlet so it protuded about a inch out of the hole. That eliminated the stain for me .

[Geoff H.]

Redcoat, I like that idea!! Yes, I have a flush mount exhaust fitting, pretty big though, and wondering why it will work at only an inch further out. But worth the try perhaps. Thanks much for the thought.

[AnchorageGuy]

Geoff, we have a 120 and have put about 2800 miles on it since we bought the boat. There is absolutely no smoke and no black stain on the stern. So you need to resolve the issue that is causing the black stain and smoke, clean it up and you should not have to make any modifications to the boat. Chuck

[Redcoat]

Geoff the extention only works for the stain. The black smoke on my boat was the result of bad injectors and charging at anchor with no load on the engine.Carbon and bypass of diesel results in minor overfueling at startup. After warming up and moving off under load the carbon burns off. Charging at anchor is the real cause. The extension allows the exhaust to not run or pool in the wake. When you place the PVC the thruhole has two ridges in there for the wrench to hold when tightening. About a 1/8 slit on both sides of the PVC will lock it right in there.

[Geoff H.]

I may have an injection pump and or injectors issue. (I don't run engine w/o a load.) I'm currently in Zihuatenejo and heading south. I suppose I might be able to find injection service in el Salvador or Panama. Thanks guys.

[svWindfall]

Originally Posted by Geoff H.

I may have an injection pump and or injectors issue. (I don't run engine w/o a load.) I'm currently in Zihuatenejo and heading south. I suppose I might be able to find injection service in el Salvador or Panama. Thanks guys.

Good luck finding anything in El Salvador, and everything in Costa Rica is way too expensive! Your best bet is Panama, there are actually good mechanics (even Lloyds of London certified) at the anchorages at Las Bresas & Balboa who can help you. Ask on the VHF net (M-S at 8am) channel 74, there are many who can help steer you in the right direction.

[Geoff H.]

Thanks sv Windfall, that kind of info is why I love this forum. Will be in Panama, the gods willing, in March. The stain is just a nuisance, but evidence of something that I'd like to figure out/repair. Thanks for the word!!