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Old 30-05-2015, 15:02   #1
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Perkins 4236 blue smoke

My Perkins 4236 was completely rebuilt in South Africa last year . After 47 hours I changed the oil and laid up the boat on the hard in Trinidad. There was no smoke and the exhaust was clean at this time. Launched in March this year And motored for about 4 hours on passage to Grenada . I was horrified to find the hull around the exhaust covered in black soot. The motor has now done approximately 80 hours since the rebuild and on startup is producing lots of blue smoke . This appears to diminish to nothing when the motor reaches normal running temperature. I have not detected any drop in the oil level on the dipstick. A local mechanic diagnosed a worn injector pump so I ordered a rebuilt pump from the USA but that does not appear to have made any difference to the smoking.
The next mechanic I consulted said the cylinders are glazed and the motor needs new piston rings. I find this hard to believe as the motor has run only a few hours without a load. Please, can anyone help?
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Old 30-05-2015, 15:30   #2
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Re: Perkins 4236 blue smoke

If the oil level does not drop, it is not an oil overconsumption.
If the engine starts well, the compression is good, the piston rings are not Involved.
And the motor has been reconstructed, so it is assumed that the injection pump has been properly seated.
blue smoke and black soot, it is a bad fuel combustion, Especially on cold engine, probably bad injector spray ?...
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Old 30-05-2015, 15:39   #3
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Re: Perkins 4236 blue smoke

Thanks for your reply. I had the Injectors checked and the spray pattern was described as good but not quite 100 % . I will have new tips fitted when I reach somewhere where these are available.
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Old 30-05-2015, 15:51   #4
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Re: Perkins 4236 blue smoke

Injectors that sat for some time may have developed minor corrosion on the tips.
Beware of Caribe mechanics! I went thru 3 on an engine problem over a period of months before getting one that knew what was wrong.
Is it blue smoke or black smoke?
Doesn't blue indicate burning oil? Black develops on the stern of a lot of sailboats after hours of motoring.
My 4-108 produced some smoke until warmed up when started cold. But didn't burn much oil.
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Old 30-05-2015, 16:05   #5
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Re: Perkins 4236 blue smoke

How is the air supply to the engine? My 4236 made a lot of smoke at one point and the issue was a slightly blocked air intake. I have also changed the injector pump and ajusting against the timing/alignment made a difference to smoke so might be worth considers also.
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Old 30-05-2015, 16:46   #6
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Re: Perkins 4236 blue smoke

Your mechanic may be right. It takes hardly any amount of oil to make it smoke. You can't just run it at "no load" just after a rebuild. This is especially true if you don't know what the cylinder surface was like afer the rebuild. You need pressure on the rings to seat them. Which means running it a rated power for a number of hours..
You may to able to get by without another hone job but it's not a sure thing. You can run straight oil with no additives for about 50 hours and see how it's doing. This what we do with aircraft engines.
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Old 30-05-2015, 17:45   #7
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Re: Perkins 4236 blue smoke

Do you overfill the engine with oil in the last oil change? the gases vent to the air filter housing, blowby my guess!!! see if there is oil in the air filter canister...
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Old 31-05-2015, 09:34   #8
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Re: Perkins 4236 blue smoke

My uneducated guess would be a slight bit of oil running down a valve guide after shutdown. probably so little you wouldn't notice a drop in amount on the dip stick.
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Old 31-05-2015, 10:48   #9
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Re: Perkins 4236 blue smoke

I think your engine is fine...but you've got some bad diesel fuel. Where did you top up last? Before the haulout? Did you use a biocide or fuel conditioner?
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Old 31-05-2015, 11:07   #10
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Re: Perkins 4236 blue smoke

Gee, I hate to jump in on this but I have a Perkins 4-108 that deposits a lot of black soot on the transom after motoring awhile. The smoke is not blue, but black. It starts and runs fine but will not come up to full rated revs.

I have been told that blue smoke means oil is in the exhaust and black means that unburnt diesel is in the exhaust. This seems right to me. I'm surprised more mechanic "sperts" haven't spoken up on this.

In my case, I think my prop is over-pitched. I was told to check the timing mark on my fuel injector system and that seems OK. The injectors are OK. The air intake is clean. From what I understand, if the timing is good and you get enough air for the proper amount of fuel then you should be good at the rated max RPM.

I am not sure if blue smoke would soot up your transom the same as black smoke but the causes and repairs are very different for each so it is important to sort that out.

I'm going to start a separate thread about the effect of motoring at different RPMs on smoke.
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Old 31-05-2015, 11:08   #11
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Re: Perkins 4236 blue smoke

Blue smoke will be lube oil, not bad combustion. Did they overhaul the cylinder head as well? If not, it maybe should be done.
Otherwise could be an overfill of lube oil, like allready suggested, or maybe wrong oil viscosity.
Is the oil pressure normal?
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Old 31-05-2015, 13:23   #12
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Re: Perkins 4236 blue smoke

First step is to check blow by.
Sounds ringish, oil ring anyway.
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Old 31-05-2015, 13:59   #13
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Re: Perkins 4236 blue smoke

Quote:
Originally Posted by sailnow2011 View Post
First step is to check blow by.
Sounds ringish, oil ring anyway.
Yeah, seems like very few read the OP, It seems to go away with temp. None of the other ideas have much to do with temp.
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Old 31-05-2015, 14:06   #14
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Re: Perkins 4236 blue smoke

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Originally Posted by Cadence View Post
My uneducated guess would be a slight bit of oil running down a valve guide after shutdown. probably so little you wouldn't notice a drop in amount on the dip stick.

My bet as well, Quite normal for people to not re-build heads during an engine overhaul, and often old valve guide seals leak, and when they do, it's blue smoke at start up, that goes away in a couple of minutes, but results in little to no oil consumption.


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Old 31-05-2015, 14:37   #15
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Re: Perkins 4236 blue smoke

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Originally Posted by a64pilot View Post
My bet as well, Quite normal for people to not re-build heads during an engine overhaul, and often old valve guide seals leak, and when they do, it's blue smoke at start up, that goes away in a couple of minutes, but results in little to no oil consumption.


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Pretty quick to blame the mechanic for doing a lousy job around here. Valve guide seals come free with a gasket set on these engines. I can't imagine not using them.
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