I had a similar problem with our Onan MicroQuiet several years back. We had pulled into a gas station and shut down the generator without letting it run for a few minutes with no load to cool down. When we tried to start it later the starter clicked but it wouldn't crank at all. I removed the generator access cover, reached in and tried to turn it by pulling on the fan blades. No luck with that. Fortunately I carry a 3/8" socket set that had the right size socket for the bolt on the fan/flywheel. It took quite a bit of effort to break it free. Started right up with the starter after doing that and no problems since.
I'll never forget the no load cool down period again!
