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Old 13-12-2015, 11:57   #1
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Lots of carbon build up in cyl #2 exhaust port

What does it mean when the exhaust port of cylinder #2 has a lot more carbon buildup on the exhaust port? I'm not sure what this means, I'm not much of a mechanic (yet).

I removed the exhaust manifold (to clean/repaint) and found that exhaust ports 1, 3, 4 are pretty clean, but #2 has nearly one mm thick later of buildup. I'll guess that the cylinder also has more buildup than others, but I don't have the mechanical balls to go that deep into the engine yet.


Engine: universal M50/5444 (v1902).
Engine was running fine and never had any problem starting or running, but i'm not a mechanic and wouldn't know bad noises/performance if it hit me in the face. There also was always a starting problem when the engine sat for a few months. I suspect air leak into fuel lines.

I am removing/cleaning/replacing parts because it's a 32 year old engine and lots of rust.

One thing I did notice is that injector #2 always had a wet look on it (the outside that is visible). I replaced all injectors (same reason, they are old) and cost to rebuild/test was more than the $60/each new.

Is there anything i should check or be worried about?

thanks
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Old 13-12-2015, 12:10   #2
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Re: Lots of carbon build up in cyl #2 exhaust port

Probably a valve guide. Live with it unless you want to pull the head and do a valve job. Slim chance you could pull the retainer and spring and put on a new seal if it has one.
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Old 13-12-2015, 13:17   #3
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Re: Lots of carbon build up in cyl #2 exhaust port

As mentioned by Guy, you could be getting some oil into the combustion chamber, either from a worn valve guide or valve guide seal, or perhaps piston rings, and this oil is showing up as soot in the exhaust port. You could also have had a marginal injector with a bad spray pattern resulting in poor/ incomplete combustion. This also could soot up the port. Sometimes if the deposit is dry, it is coming from fuel, and if it's wet, it's oil.

Since you have changed out the injectors, that possibility is eliminated. I think if the oil level isn't going down, and the exhaust gasses aren't overly blue, just keep an eye on it and see if it progresses.

DougR
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Old 13-12-2015, 13:21   #4
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Re: Lots of carbon build up in cyl #2 exhaust port

Black soot is from under burned fuel! If you had an issue with external fuel leakage, then #2 injector probably had internal issues as well. The fuel on the out side is usually caused, by a loose connection, or bad feral seal under the nut. During lay up the fuel would weep out, and if you had a problem with the engine starting, it was probably caused by the air that displaced the fuel in the line. Also if the injector bleeds down during shut down, ie when engine is not running, this will cause excess fuel to slow combustion, sooting up that cylinder. It would be worth having the #2 injector pressure tested to see if it holds or bleeds out.
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Old 13-12-2015, 13:40   #5
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Re: Lots of carbon build up in cyl #2 exhaust port

Quote:
Originally Posted by scherzoja View Post
What does it mean when the exhaust port of cylinder #2 has a lot more carbon buildup on the exhaust port? I'm not sure what this means, I'm not much of a mechanic (yet).

I removed the exhaust manifold (to clean/repaint) and found that exhaust ports 1, 3, 4 are pretty clean, but #2 has nearly one mm thick later of buildup. I'll guess that the cylinder also has more buildup than others, but I don't have the mechanical balls to go that deep into the engine yet.


Engine: universal M50/5444 (v1902).
Engine was running fine and never had any problem starting or running, but i'm not a mechanic and wouldn't know bad noises/performance if it hit me in the face. There also was always a starting problem when the engine sat for a few months. I suspect air leak into fuel lines.

I am removing/cleaning/replacing parts because it's a 32 year old engine and lots of rust.

One thing I did notice is that injector #2 always had a wet look on it (the outside that is visible). I replaced all injectors (same reason, they are old) and cost to rebuild/test was more than the $60/each new.

Is there anything i should check or be worried about?

thanks
Carbon buildup comes from unburnt fuel or oil.

Check compressions, wet and dry. This will indicate if you have problems with your oil contol rings. You may or may not see blue smoke.

If the engine has overheated sometimes your oil control rings will lose their tension. However you mention one cylinder so I'd start diagnosing the fuel system.

A leaking or dribbling injector could lead to carbon buildup. You would typically see black smoke if the engine is overfuelling.

$60 an injector sounds cheap. What was done?

Note that diesels last when fed clean air, clean fuel and clean oil and they are run at temperature for long periods.

Make sure your fuel filtration system is up to scratch. We run a 30 micron primary, 10 micron secondary and a 2 micron final fuel filter.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
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Old 13-12-2015, 17:16   #6
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Re: Lots of carbon build up in cyl #2 exhaust port

Thanks for the advice.

I checked exhaust port #2 and the build up is dry and crusty.
Based on what ya'll said and what I have seen (no oil loss, no smoke, leaking #2 injector, dry buildup)

I think I'll ignore the build up for now.
The fuel filter system is good (new tank, Racor 500, then on-engine filter. Separate recirc system with it's own racor 500 and a larger filter, name/poresize I forgot, but most engine hours were put on by PO before I redid the filter system.


LeftBrain, that $60 injector was the price for a new one from kubota, not a rebuild/clean. I'm probably going to chuck the old ones because cost of new (~$60) is cheaper than rebuild.

Now, I have to learn how to adjust valves and the decompreesion lever. A PO or PO's mechanic adjusted the decomp lever and it wasn't movin. it was totally stuck in the "compression enable" mode. I tore the rocker cover and decomp lever apart, cleaned them and reassembled. Now the hard part, putting it all back together correctly.

Working this diesel engine is getting less scary with each part I remove, clean, and put back on.

One day I might go sailing again!

Thanks again for the help.
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Old 14-12-2015, 08:31   #7
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Re: Lots of carbon build up in cyl #2 exhaust port

I agree with all the advice except I would not assume the brand new injector is working right, and as the other poster said, I'd want to get it tested. Not so much to fix a so-far minor problem but because I don't know enough about diesel design to feel confident it can't make the engine fail to start when I really need it.
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Old 14-12-2015, 11:32   #8
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Re: Lots of carbon build up in cyl #2 exhaust port

It is probably from over fuelling that cylinder.
Keep a check on the oil consumption, but I think you've cured the cause of the carbon build up
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Old 14-12-2015, 11:42   #9
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Re: Lots of carbon build up in cyl #2 exhaust port

My vote is the valve seal or guide .
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Old 14-12-2015, 12:21   #10
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Re: Lots of carbon build up in cyl #2 exhaust port

Normally dry soot, as in lamp black perfectly dry, is fuel, usually an injector either opening at too low a pressure, a bad spray pattern or both. It's possible even a new injector could have a clogged tip or be shimmed wrong, injectors I have been around, the pressure is set by shimming the spring.
If it's oily and greasy, it's oil of course, either from valve guides, or rings.
If it's fuel, I'd try to correct it, if it's oil, I'd run it until it lost power, got hard to start or started smoking up the neighborhood.
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