I crashed in practice and damaged my gear linkage, leaving me with no 5th and 6th gear.
I had badly worn rings.
I was running a tight squish band for short circuit track.
I had to over-rev in 4th to try to keep up.
I think it was down to a type of detonation where the hot gas finds a way through the easiest passage (the ring gap) and keeps burning away in that specific point.
Did you have anything like this at any time recently?
It's a theory, but I don't know for sure. Welcome to the twilight zone!
