@CYBER-NINJA looks like an older style model by the looks of the tank, probably just in sumo trim.

I had the same issue with that sprocket nut too. Main problem was that I had already taken most of the engine apart.. Took a good couple of hours to get that thing off in one piece!

@Calum I've always used Loctite stuff for the cases, seems pretty good.

Think it's this one
http://www.ebay.co.uk/itm/LOCTITE-515-Anaerobic-flange-GASKET-sealant-GLUE-50-ML-B-B-04-2018/261831854946

You tried something like this?

http://www.ebay.co.uk/itm/352053460833

With the bike completely cold, fill up the radiator, then fill up the expansion tank between the min and max marks.

@declan If you expansion cap is shooting off, I doubt the underlying issue has been solved. You may be burning coolant in the long term.

Head warped maybe?

@jgr72 nice