Well guys, mission accomplished. The Builder was rescued. No sticks, no extra engines, just one nephew. He gave it a push and the second engine sputtered a bit, but stayed on enough to keep the train moving. It made it all the way through the yard and started back up the helix. I didn't notice that I had left half the train behind at the bottom, until it came out light at Red Wing. He pushed the cars up the helix and I put the train back together.
I took the bad engine, flipped it over and looked at the rollers. As I had suspected, they were filthy. A couple drops of hair clipper oil, and a quick spin with a wire brush in the Dremel, and they were clean and shiny. Back on the rails and in the train, throttle up and no more sparks. Jim asked last night, how did I know? Not my first rodeo.
How did they get so dirty? I'm running trains in a construction zone. Dirt gets on the track, in spite of running the track cleaning car. The sparks start slowly, but then they snowball, and before you know it, your engine's rollers aren't getting any power through to the motors.
If it is your first rodeo, and you see sparks coming from your rollers, Take a minute to check them and clean them.
