Thanks for all the good ideas and information on the generator! Isolating it to a problem in the diesel engine and not somewhere else was the first challenge – we couldn’t tell where the noise was coming from. The fact that there was back smoke and that the frequency fell off should have been our first clues to go right to the engine.
So after some scratching of heads we too decided that it was something wrong with the combustion. We checked the air filter and saw nothing major, so we next switched to inspecting the fuel system.
The engine runs from an 80L fuel tank that sits above the engine next to the control panel. The fuel leaves the tank from a small port on the bottom of the face of the tank and goes to a low-pressure fuel pump. From the low pressure pump it goes through a fuel filter, the governor system, and into the high-pressure pump before going into the injectors.
Next to the port on the fuel tank is a drain plug that you are supposed to use once a week to drain the diesel sludge that settles at the bottom of the tank. It turns out the sludge had not been drained in the past FIVE years to anyone’s knowledge. I think we found the root of our problem. The small filter on the low-pressure pump was coated with a thick layer of grit and junk. We took the whole fuel tank off and washed it out, we replaced the fuel filter, and cleaned all the lines as best we could.
After clearing all the air out of the fuel lines we started it up again and it has continued to run fine. So the answer to this one is that sludge in the bottom of the fuel tank was clogging up the fuel system.
Such a simple problem could be solved with good maintenance practices, but it has been difficult for a technician to know what good practices are when they come and go every few years. The only way to learn that the maintenance is insufficient is to run into these problems and then try to sort out the shortcomings of the current maintenance regime. The lesson from this experience is that the breakdown and repairs need to be well documented and the maintenance schedule should be written down and refined according to the performance of the generators - but lots of prayers and banging on the generator with large objects seems to go a long way too!
Never would've guessed it was fuel supply and not air intake, but makes sense when you think about it. At the ski run, we struggled with starting the rope tow most mornings when the temp was less than 40. In other words, it was fairly reliable in the summer and on days when the snow was turning to mush. But when it was good and cold out, or right after a nice dump of new snow, it was a real struggle to get it running. Often it meant skiing back and forth from the motor house to the parking lot to "borrow" somebody elses car battery when the first ones ran down. Ever thought about trying to ski while carrying a car battery? Anyway, it turned out that most of the problem was due to the manager (Milan Moody) who thought it prudent to just add more oil to the engine when it was low and not worry about ever changing it since it went thru about a quart every 15 - 20 hours. Plus he figured since it used so much oil, we should buy the cheapest we could find, parafin based, nice and thick, usually plenty dark too. Eventually, I got tired of having to fight with it every time it got cold so I changed the oil, spark plugs and filters in hopes that would make a difference. Naturally it made a huge difference and the motor was easy to start for several seasons, even when it got cold. Eventually, the fuel system started acting up usually right about the time when we had the highest number of riders waiting for a lift up the hill. Turned out to be pin-hole leaks in the bottom of the tank near the up-take resulting in "vapor lock." But that's a whole nuther story.
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