Generator problems that I run across most often are due to: 1 long periods of not running. 2
Corrosion due to Generators getting wet 3 Bridge Rectifier failures (Westerbeke). 4. Gasoline generators are prone to "gumming up" the carburetor due to the new "Government (read ethanol)
fuel.
One example of a major generator failure occured to me on a yacht that was kept in "mothballs" in
Florida for a few years......The generator ran fine for about 20 hours.
Then, at an anchorage in
Nantucket, WHAM smoke.....lotsa smoke....sparks.....
The windings shorted out.......come to find out, that the shellac that
seals the windings is great
food for some bacteria/bugs........it only took one bare wire to cause the whole mess to blow......By running the generator frequently and getting it up to heat kills those varmints.