[Richard]

This will probably be a multi installment read, so get a cup of joe or whatever. Hopefully you will enjoy. 

For about five years my generator engine would periodically produce black smoke, not grey, not white, black. That is usually a sign of incomplete combustion in a Diesel engine. Because our generators are oversized for most of how we use the coaches, the engine runs at partial load and has a tendency to build up carbon in the cylinders. The carbon build up can interfere with the valves sealing, or the piston rings sealing. Both conditions lead to low compression and black smoke. Also, the injector tips can foul from the carbon build up leading to poor atomization of the fuel. That too will cause black smoke. Other potential causes are air intake restrictions, exhaust restrictions, cold engine, low fuel pressure, and improper fuel injector pump timing. Can you already tell I noodled on this a long time? 

My usual fix was to load the generator as much as possible and “burn off” the carbon deposits. This worked a few times. I also tried every magic fluid out there as a fuel additive, sea foam, marvel mystery oil, acetone, ATF, and pee from an albino raccoon. None of it really helped in the long run. 

Did I say I was smoking and really wanted to stop? Did I say it was embarrassing to enter a campground and have onlookers ask if I was on fire? Did I say that this war on smoke became extremely personal the longer it continued. 

New air filters, fuel filters, turbo, and injectors ($$$$$) did not really help. As the years go by, the black smoke is no longer intermittent, now it’s all the time. The heavier the load on the gennie the worse the smoke is. 

So a deeper dive was on the list for winter projects. Someone is going to ask, how many hours on the gennie, 6000. 

A couple of other important points or clues. The engine did not use oil, not one pint in 100 hours between changes. The engine was quick to crank, even on really cold mornings. The engine did not struggle to make 50 amps on each leg. The engine ran smoothly, well as smoothly as a tractor engine runs. 

Given all that the first diagnostic is a compression test. Well this is interesting because hooking a compression tester up to a spark plug hole is not going to work. It’s even more complicated because none, including the Yanmar, commercially available testers I could find married up to the injector hole. Maybe one is out there, I just didn’t find it. So, I made one. I took one of the old injector bodies, welded ears on it to match the injector hold down screws, and gutted the inside. I hooked that up to a high pressure gauge with a check valve and pressure relief valve in the appropriate places. This first pic is of the home made compression tester. Second pic is of the modified injector to fit the injector hole. I sealed it to the bottom the injector hole with an o ring. 

The compression readings on a cold engine that had been sitting for a couple of months were around 300. Not terrible, but the Yanmar manual says it should be 350 or above. 

The next step was to remove the one way check valve on the compression apparatii, and use air pressure to do a crude leak down test on the cylinders. So I learned a few things here. One the piston of the cylinder you are going to test should be at top dead center. Ok, got that. Two, install a regulator on the air line feed. When you apply air pressure to the top of the cylinder, the crank WILL turn. It’s a 3.5 inch diameter piston, so 100 psig is 960 lbs force. It’s a bit hard to hold the breaker bar on the crankshaft for a wimp like me. Any Hoo, 100 psig was not necessary, for as soon as I applied air to the first cylinder, I heard a lot of air escaping into the exhaust manifold. Only way that happens is if the exhaust valve is not sealing. At this point, I didn’t do any more testing, because I knew the head would have to come off.