MY 284 has a 2 year old starter and all of a sudden It would not turn over. I hear a click when I push starter button (key went bad years ago) I replaced solonoid because I couldn’t even cross poles on that to start it. Still no luck with new one. Battery is fully charged and also only a year old.
After checking all of the electrical connections, try getting the engine to turn, at least a little. Pry bar on the front crank pulley or put it in gear and rock the rear wheel with a board or something. It is possible that the bendix is just jammed against the flywheel and rotating the crankshaft a little will free it. It is also possible that the starter armature is just sitting in a “dead” spot that it can’t turn itself out of.
The next step is to pull the starter. Fortunately it is easy to do. Then some bench testing will show you what is wrong if indeed it is the starter.
Have you done a load test on the battery? If you don’t have a load tester put a voltmeter on it and make sure it has at least 12.5 volts with everything turned off. Then watch the voltage while you turn the key to attempt a start. If it drops below 10 volts, the battery may be the culprit.