Originally Posted by Kioshk
When I get a new engine, I always disassemble it so I can make sure everything's in good order and will replace sub-standard parts. I also slather the clutch-axle (and spring) with common bearing-axle grease. Works great. That portal is meant to allow greasing access AND access to the spring tensioning nut. Adjusting it affects resting clutch-plate pressure.
I knew the hole went all the way through to the crankcase but didn't know it had a purpose, THANKS Kioshc.