I have the top end off my RT2 360. On taking the compression release components out of their threaded aperture I notice a hole in the top of the threads about 5mm in. There is a matching one 180 degrees opposite. I attach a link to the picture on IMGUR. 
imgur.com/E7H6Alr
The hole was (and still mostly is) filled with a resin like material which I initially scraped away but before I have someone look at this cylinder head with a view to cleaning it up and then possibly machining the bore etc. I wondered what this hole was all about and whether it should be open or bunged up as mine currently is?
imgur.com/C4d9jUX
Any advice welcome.

I raised this a few years ago (thread has probably been archived) and yes, that resin is meant to be there. Something to do with filling in a hole that was needed for machining of the decompression valve aperture. 

Ok, thanks, I'll won't try to dig it out then.

Hope this works, on old phone. Blocked hole was from drilling down to the exhaust port exit for the valve to bleed compression out to. Had to start drilling from up there or wasn’t possible. Then had to block it off or valve would bleed off up ‘& down’. If the down hole is carboned up I think you can get at it on an angle from the bottom with cylinder off & a long drill as hole goes angled from top to bottom. On rethinking that I wonder why they didn’t drill from bottom to top & avoid having to  
make a hole then resin it. Maybe not accurate enough. My thoughts anyway. So be sure both cylinder & down holes are clear.