sorry my typo error its the left hand engine cover over the generator and sprag clutch. got a big hole in it where the gear runs from the starter to the sprag clutch.
keith.
Are you starter gears worn ? as thats what may of caused it to go ,i had a grinding on startup on my old bike and when i broke the engine i found the clutch casing had broken up and one of the lugs has gone round and cracked the R/H casing
If not chemical metal makes a good permanent repair if done properly