bertram31.com

Good morning Faithful.
finally got around to starting up one of the rebuilt 6bta engines (0970), and at the end discovered an issue. My buddy and i ran it for about a half hour at different rpm's to make sure everything was sealed, and that we didn't have any leaks. oil pressure, water temp, and raw water discharge was great.
we turned it off, let it sit for about 15 minutes, and then decided to let her run one last time, before throwing the bed sheet over her and pushing her back in the corner of the garage.
well, everything was happy, happy, until there was diesel coming out the exhaust side of the turbo. that's when i got that sick feeling in my stomach, and called it a night.
any idea's of what's going on before i start looking deeper into it?
as always, thank you.

Are you sure that it's diesel and not motor oil? Is the oil over full?

Was the engine close to sitting level while running, or was the ass end maybe down quite a bit?

After you ran it for the 30 minutes, did you idle it for a few minutes to cool the turbo before shutting down or did you shut it down hot?

Is it possible that your crankcase isn't venting pressure properly?

Mike,
it's definately diesel.
the engine was sitting level
yes, we idled it for a few minutes before shut off
there is no obstruction at the venting nipple.

the engine seems to be running rich, maybe a valve seal or re -setting of valve lash?

It is probably what is referred to as "Diesel Slobber". When the engine doesn't have enough load on it all of the fuel is not consumed. The excess goes out the exhaust mixed with soot and forms a black slobber around the exhaust. Farmers deal with it all the time on tractors that run low load applications like augers. It will build up at the top of the exhaust and then run down the side of the tractor. The cure is to take them out and run them under a good load, such as tillage. That will burn all of the residue out. In your case there is also probably not enough load to fully seat the rings on a newly rebuilt engine and that just adds to the problem. This phenomenon also leads to the problem of "wet stacking" in which the unburned fuel from an idling unloaded diesel washes off the oil on the cylinder lining and leads to excessive wear and fuel dilution of the oil. Put them in the boat, run them hard and all will probably be well.

Rawleigh,
that completely passed my mind, but would make very good sense.
we've had that issue on some standby genny's for our pump stations here at work.
it would be a silver lining w/ this project, if that's the case....
thanks

I vote slobber. But the good news is that even it is not slobber, it is more than likely just an injector issue. Injectors are cheap and easy to access compared to everything else on that engine. Run it under a load, if it is still doing it, pull the injectors and have them tested. Any decent injector shop can tell you if they are tight and popping at the correct pressure.

When the engine doesn't have enough load on it all of the fuel is not consumed. The excess goes out the exhaust mixed with soot and forms a black slobber around the exhaust.

Thanks Rawleigh, you just resolved an issue that's been bugging me with my Yanmar 315's for years. We tend to run at low rpm's (2500-2600 usually because there's so much drift in the waters up here) and the boat is pretty light so I bet that soot buildup on the transom is from lack of load.