Yanmar diesel engine

Mith

Active member
I've been meddling with a Yanmar 4HP single cylinder diesel engine today. Got it running after a rebuild.
Anyway, it runs just fine, however, it gives out quite a significant amount of white smoke.
I understand this would indicate there was too much fuel being injected. Any thoughts as to why?
Would the injector being worn cause this, and is it likely the injector might be worn (its been used enough to require a rebuild....)?

Just seen the time and gotta dash, anyway, TIA.....
 
B

bczoom

Guest
I understand this would indicate there was too much fuel being injected. Any thoughts as to why?
Come on Jim... You're too smart to ask such a silly question. It's obvious you overfilled the fuel tank and it's getting too much fuel. :whistle: :D :poke:
 

Grrrr

Member
White smoke comes for a variety of different reasons but often because of too much fuel is being forced in or water is getting in.

I suppose it might be that the injector has got a bit leaky and worn if the engine is well used
 
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Mark777

Member
Mith,

bczoom's statement is pretty close. Excessive fuel is a strong indication when white exhaust is present. And unless the single cylinder is water cooled with a bad head gasket...it may be the only plausible answer. An injector with weak cracking pressure (timing) will cause thick, white smoke.

Pulling the injector and reconnecting the fuel pipe, sitting it part way in a coffee can and observing the spray pattern should help in diagnosing the problem...If the spray is cone shaped and even, then the injector is OK. Anything else, like slobber, dripping or uneven hemispherical spray patterns are a dead giveaway and the injector should be rebuilt or replaced. Keep your hands away from the end as they open (crack) at about 350#'s, which seems extremely high...but not when you're talking nearly 20 to 1 compression ratio.

Mark
 

Mith

Active member
Brian, honestly, you mock my wifes name (SWMBO) and now you accuse me of overfilling the diesel tank! :ohmy:
:yum: :yum:

Mark and Jake, its air cooled, so I guess that really does narrow it down to excess fuel.

Mark, the injector sprays an even fan pattern, kind of like a firework exploding if you see what I mean.
Sounds like the cracking pressure may be wrong, might it be time for a new injector?
 

Mark777

Member
Jim,

Can't think of anything else it could be....

There is a remote possibility (and usually created by excessive ether starts) of a cracked or broken swirl chamber. It is the cone shaped, (like a sharp pencil) metal piece installed in the head. It has 6 taper-drilled orifices for the final fuel delivery at the top of the piston. If it's distorted or broken, it can disperse fuel unevenly and create pockets of unburnt fuel.....

Were you able to check the ring gap during the overhaul? And cylinder taper measuring with snap gauges and a micrometer? Or the poor mans method of measuring the ring gap at the top and bottom of the cylinder wall?

I'm wondering if what appears to be excessive white smoke may be a combination of unburnt fuel AND poor compression. These Yanmar engines are notorious to keep on plugging along even with worn rings with gaps larger than .065 (and bigger). This happens often and long before your exhaust changes from gray-white to blue-black. Yet people continue to use them even though they become harder to start...enter the dreaded 'ether' which usually makes the difference between a scheduled overhaul into a worthless boat anchor.

Just tossing out bits to ponder.........

Mark
 

Mith

Active member
Mark, I wasn't really looking for damage on the head when I rebuilt it, so I'm afraid I cant comment on the condition on the swirl chamber.

The rings were replaced as part of the rebuild, and I do recall them being pretty tight, though I didn't measure.

The engine as rebuilt due to low compression, and therefore being hard to start. I now starts on the first pull, so that has been remedied.

Sounds like I might need to pop the head off and check out the ring gaps and swirl chamber.

Thanks for the help, exactly what I needed.
I usually only work on petrol engines, this is my first step into working on diesels.
 

Mark777

Member
I agree ribchord....

Mith, never did hear the outcome of what the little one banger needed?? Did you pull the head and/or replace anything??

Mark
 

Mith

Active member
Mark, someone else finished off that engine, so I'm not sure what happened. I *think* it might have received a new injector.

Either way, now I've had a go with diesels I'm itching to get one for myself again. I'd quite like to get a nice 2 or 3 cylinder on the bench for rebuild.
 
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