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Old 04-08-2008, 12:50   #1
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Yanmar started smoking

I am a one man anti smoking campaign so when my Yanmar started emitting a puff of black smoke on start up I was most distressed.

The puff appears to come from the breather. At first I thought the turbo wasn't turning but it is free and smooth.

A mechanic has told me Yanmars do that and not to worry.

My CO detector in the saloon is worried about it however or at least it thinks it is based on the noise its making.

This is a new symptom. The engine has never done it before. No Yanmar I have ever seen did it.

Any ideas?
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Old 04-08-2008, 14:09   #2
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Black smoke at startup is from a normal overpressurized combustion chamber, where more fuel than needed is injected to start the engine. Basically you've got a cold incomplete burn. The diesel engine compresses air and fuel (at something like 400psi) enough to get hot and explode. During startup, an extra amount of fuel is injected to increase this process. When the motor warms up, the black smoke seems to clear.

Also, do I understand you correctly, that the black smoke coming the wrong way out of the intake and is getting caught up in your CO2 detector. Definitely I don't know what's going on there. Everything else seems normal.
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Old 04-08-2008, 14:58   #3
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I have seen black smoke at exhaust outlet but never coming out of the air intake. If the engine runs for more than 30 seconds you can't breathe in the saloon or the engine room. It is clearly a continuous exhaust leak with no apparent break in the system.
Its coming out of the air intake.
The engine runs and sound normal for the most part.
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Old 04-08-2008, 15:04   #4
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Bill, Let me get this straight. There is air with smoke coming OUT of the intake but the engine is running. I am not sure that is possible since if the air intake is cut off the engine can't run. It is not possible for air or smoke to both come in and out of the intake at the same time.
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Old 04-08-2008, 17:32   #5
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I have seen that on a couple of Yanmars...not turbos....ended up being a valve problem specifically intake valve
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Old 04-08-2008, 19:30   #6
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Chuck, I'm no rocket scientist and I didn't stay at a holiday inn last night but even I can understand what you are saying.

On start up I get a very black and thick puff from the air intake. That single emission must be responsible for the smell and alarm. I have only run it for seconds at a time since this condition started.

So what I am actually getting is the equivalent of a backfire on start up.
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Old 04-08-2008, 19:38   #7
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Bill, My Yanmar has a hose from the valve cover to the air intake breather, not a turbo, and I could see under certain circumstances this hose could emit smoke. Not being an engine mechanic I have been around these engines for a long time and not seen anything like this.
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Old 04-08-2008, 21:13   #8
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Seems like it could be either an intake valve(s) hanging open a bit, bad injector(s) or maybe injection timing incorrect. If it runs fine otherwise, and the smoke goes away after a minute or so I would suspect valves. If it continues I would guess injector problems. If the engine is running rough it could be timing (problem in inj. pump) although this is a remote possibility.

I've had a Cat diesel start and run backwards and there was a lot of smoke coming out the intake, but that was in a truck that compression started in reverse (long story).

Good luck, John
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Old 04-08-2008, 23:55   #9
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What do you want to do?

To me it looks like your choices are :-
1) Ignore it and hope your mechanic is right.
2) Cut your losses and buy a new engine.
3) Indulge in minor/major surgery.

If the choice is 1) then continuing to run the engine if it is a valve problem could be expensive, forcing choice 2).
If 3) is the choice then removing the valve cover may disclose the problem. Check if replacement gaskets are available.

If it is a valve problem then a broken spring could be the culprit. Our friendly Yanmar experts may be able to assist.

How much do you like working on old engines?
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Old 05-08-2008, 00:48   #10
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Lets get some sensibility here folks. Firstly as Chief has stated, you may have a burnt intake valve.
You can't have a valve "hang". That would instantly have a very audible an frightening hammering noise followed by much smoke everywhere and the need to rebuild the engine. There is no wondering about that fault.
It won't be timing. Timing doesn't just slip in a Diesel and even if the timing did change, it couldn't do what you describe.
There is one other possible, but it won't be black smoke, more blue and that is sump compression blowing through the sump breather which connects to the air intake manifold. However, to pressurize the sump, you have to have bad rings and thus you wills see much smoke at the exhaust as well. So seeing as that is least likely, lets go back to the intake valve. There is a chance you may hear it when the engine is running, but the best way to test for the problem is with a leakdown tester. This is a gauge that you connect to the cylinder at the injector port. Compressed air is forced into the cylinder. The gauge reading tells you how much air is escaping somewhere. Your ear helps you detect where the air is escaping too. If it is a burnt valve, you hear the air escaping back into the intake manifold.
Burnt valves can be caused by several issues. Incorrectly set valve clearance and even a faulty injector. If the spray pattern is wrong, it can spray onto or in the direction of the valve and create too much heat on or around the valve face.
I suggest you do a leak down test. If you have a burnt valve, the longer you leave it, the more damage you are causing to the valve seat which is par of the head.
Oh and Cylinder pressure, think more in terms of thousands of PSI, not hundreds. You can not get an over pressurized cylinder burn. Unburnt fuel that has taken one complete trip around so as it remains in the cylinder when the injector squirts again, does not burn the same as the new injected fuel does. Diesel has to be atomized before it will ignite. unburnt fuel that has touch any of the internals will not burn. In fact unburnt fuel can actually flood the cylinder and rob enough heat to stop the next dose of fuel igniting at all. Instead the fuel burns much slower and very much later in the cylinder cycle and results in blue smoke. The same blue smoke you often see at start up of a cold engine. That blue is caused by Diesel and oil being heated and burnt off outside of compression.
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Old 05-08-2008, 02:07   #11
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there is no reason on any kind of combustion engine for exhaust smoke to be coming from the air intake while the engine is running. if there is you have a serious problem.

you may want to verify that it is not just an oil leak / gasket failure. you also need to verify if it could be a fuel leak which could be extremely dangerous. oil smoke by the way will look blue. fuel smoke will be billowy black.

one other thing (i don't know much about yanmars but I am a home mechanic on my own cars, skyline and rx-7 both twin turbocharged) is that your turbo might be spewing oil either through the turbine itself or through its intake. it could be causing the smoke when you start the engine. check your turbo (housing and turbine wheel) for any cracks and shaft play.

take your boat to a mechanic if you can't find anything wrong with it.
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Old 05-08-2008, 07:01   #12
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Thanx Alan.

You stated that quite well.
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Old 05-08-2008, 09:32   #13
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Give this site a try......

Yanmarhelp.com Message Forum - Yanmar marine diesel engine help & advice (Powered by Invision Power Board)&

Lots of smart folks and a few good mechanics.
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Old 05-08-2008, 09:52   #14
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Could it possibly be an intake valve adjusted a little bit too tight?
Upon warmup the valve lash would relax just enough to operate normally?
Just a thought.

Steve B.
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Old 05-08-2008, 13:24   #15
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Quote:
Could it possibly be an intake valve adjusted a little bit too tight?
No because it's the opposite way around. When an engine is cold, the valve train is at the most slack. As the engine warms up, the expansion of components takes up all the slack. This would mean the valve would be closed when cold and would open as the engine warms up. That would also take several minutes, not just a revolution or two or three. That would also result in the valve burning and being cut away fairly quickly, which would result in the cylinder pressure being down in the one cylinder.
Hmmm, never heard of the colour "billowy black" :-) I wonder if a paint company would include that on their paint chart sometime. In regards to the turbo, oil seal leaks wil result in huge amounts of oil smeared all through the down stream air intake area. A turbo would make it even less likely a "puff" of exhaust smoke would make it back out of the intake. It is also highly unlikely any one would be able to know if the bearing is worn by visually or physically with your fingers, checking it.
However!, Silentoption has not stated that there is a Turbo fitted, so lets not get side tracked until "SO" can confirm.
BUT!, "SO", it would be a very good idea to check the exhaust manifold if it is not a jacketed manifold. I am pretty sure yanmar water cooled their Turbo's, so the manifold and turbo should be jacketed. Chief can you confirm that???
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