Sudden loss of power and grinding noise

[ImpulseRocket]

I’ve checked all that. The small bevel gear seems to be quite far out away from the engine but it wouldn’t explain why it only makes noise when it’s warmed up

Have a picture of it? is there any marks on the inside of that side cover from the bevel gear?

 

[machanic]

Have a picture of it? is there any marks on the inside of that side cover from the bevel gear?

Also a picture of the end gap of the lower piston ring, something looks odd there in your previous pic but can't see it well enough to tell