Yanmar diesel smoking/ black soot

[Bronk33]

Originally Posted by AlwaysFORSAIL

Your engine is near death. You have a rebuild or new engine in your near future.

Care to elaborate?

Motor isn't original and has low hours.

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[a64pilot]

This is what confuses me, Diesels have no throttle plate, RPM is controlled by fuel only, when out of gear, how can he have excessive fuel?
Increase in fuel should give an increase in RPM, unless the injector spray pattern was really bad or timing out, then you could get too much fuel without an increase in RPM.

Injectors were inspected right? Any way they can be incorrectly installed?

Injector fuel pressure way out of spec, too low?

The not responding to throttle correctly means something and jogs a memory, but I can't remember. I'd be prepared to put a board over the intake in case she runs away.

Are there crush washers between the injector and head, were the old ones left in and new ones added? Sorry I have no idea how these injectors are installed

[a64pilot]

You absolutely sure nothing is blocking the intake, keeping the engine from getting an unrestricted flow of air?
Remove the intake silencer to be sure

[tdh1849]

Call " Complete Yacht Service" Yanmar dealer in Ft.Lauderdale, ask for the owner, Mark,( USMC) tell him Pat N, formerly of Lauderdale now in Tampa told you to call.
Ask him, he knows everything there is to know about Yamars.............

[Ti' Punch]

Don't forget to replace your thermostat too. That's not causing your black smoke problem, but should always be replaced after an overheat situation.

[sailorchic34]

Originally Posted by a64pilot

This is what confuses me, Diesels have no throttle plate, RPM is controlled by fuel only, when out of gear, how can he have excessive fuel?

The amount of fuel injected at a given throttle position is set by the injector limiter. Normally this is set at the factory and never touched again. It's sort of a mixture control. On the yanmar gm's turn counterclockwise enrichens the mixture, clockwise leans it out. Too rich and the engine smokes black, too lean and you'll burn a piston. It's not a normally user adjusted item, but it's there. Black smoke is a sign of a too rich condition. Normally a fowled prop causes this as the governor tries to compensate.

Something has changed the mixture, either the injector pump was somehow damaged by the excess heat or governor springs, or pressure plate between fork and governor collar on governor were effected or even the tiny spring under the tiny bronze nut on the injector limiter.

[a64pilot]

SC, but you can't change the mixture of a Diesel, it's constantly changing as there is no throttle plate to restrict air flow, a Diesel ingests the same amount of air it Idle as it does at full bore, or close to it.
A spark ignition engine of course "throttles" both fuel and air, but a Diesel doesn't, a Diesel only is throttled by fuel.
Add fuel to a Diesel, it accelerates


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[wesevans]

Have you checked compression? Some older diesels with worn pistons/cylinders smoke (low compression) You may need a top end rebuild. Sounds like you need a complete check out by a mechanic.

[Nicholson58]

Originally Posted by gah964

its not the injectors its a cracked ring

My first guess as well or loss of compression in at least on cylinder. Compression test is cheap. The repair is not. For this vintage engine assuming no rebuilds, you may be looking at serious work. Also, I suggest you add a temperature gauge on the binnacle. Your observation that the engine runs a bit better or at least less smoke after warm-up may mean the ring(s) only worn but not cracked. Same labor job either way.

[sailorchic34]

Originally Posted by a64pilot

SC, but you can't change the mixture of a Diesel, it's constantly changing as there is no throttle plate to restrict air flow, a Diesel ingests the same amount of air it Idle as it does at full bore, or close to it.
A spark ignition engine of course "throttles" both fuel and air, but a Diesel doesn't, a Diesel only is throttled by fuel.
Add fuel to a Diesel, it accelerates

That is all true, but not everything there is to it. Unlike on a gas engine where the throttle connects directly to a butterfly regulating air volume, Diesels regulate by fuel volume.

When you advance the throttle on a diesel it dies not directly move the injector rack, It put a bit more force on the governor to open the rack a bit more.

The governor is directly connected to the injector rack and it sets how open the rack gets based on load. The problem with diesels is there really isn't a throttle. Diesels what to over rev. But the governor system is used to regulate the position of the rack, so the engine does not over rev. The injector limiter sets the maximum open distance on the rack. The governor controls the rack for the given load. So you can actually adjust the mixture of the rack by setting how far the governor will travel.

If the injector pump is damaged that can also let too much fuel by.

Not sure if that clear or not. I've attached a PDF of the governor linkage on the GM series. The throttle/ speed control has a spring between it and the governor assembly.

[ramblinrod]

What temp is the engine running at now. Low temp produces black soot. If temp is low, check thermostat is not stuck open.


Rod Brandon

[DeepFrz]

An explanation of diesel engine smoke.
Diesel engine problems: black smoke explained

[jimbunyard]

Another suggestion; I tried earlier to look up the actual injection pump you have, to no avail. If the pump illustrated in Sailorchic's post #40 is your pump, it's fairly easy to take it completely apart and re-assemble it. There are no rubber components, but the plungers and bushings and the rack mechanisms must be clean and without restriction of movement. It is reasonably likely that a severe overheat could have carbonized some fuel and restricted either the p&bs or the rack, restricting their travel.


I'm well aware that the books say one should leave the injection pump
(or unit injectors) to the 'experts', but I've done this successfully on Universal, Cat, Perkins, Volvo and Detroit (injectors) engines. One must be methodical, precise and clean, but it's certainly within the capabilities of a patient, experienced amateur....

[gah964]

Originally Posted by Nicholson58

My first guess as well or loss of compression in at least on cylinder. Compression test is cheap. The repair is not. For this vintage engine assuming no rebuilds, you may be looking at serious work. Also, I suggest you add a temperature gauge on the binnacle. Your observation that the engine runs a bit better or at least less smoke after warm-up may mean the ring(s) only worn but not cracked. Same labor job either way.

Most people will avoid the real problem because the problem is scary.
Look people its freaking simple run the engine put your hand over the exhaust if you you have a hand full of oil get a new engine.
Or get a compression check or waist money with sailorchicks theory.
It may be a fuel dump but a fuel dump is white smoke not black!!!
but what do I know I only rebuild engines.

[gah964]

Originally Posted by DeepFrz

An explanation of diesel engine smoke.
Diesel engine problems: black smoke explained

blue smoke lean mix
black smoke oil burn
white smoke fuel dump
that article is mixed up no pun intended