@Mightyman said in Overpressure in cooling system:
Man that engine does sound sweet!
You shouldn't really remove that cap when the bike is warmed up as there is always going to be some sort of pressure in the system. I don't actually know if your video shows TOO much pressure though. Anyone else?
Yeah, I know there are supposed to be some pressure, but this is definetly too much, i've filled the system a number of times by now, and i've never noticed anything like this before 
@Calum said in Overpressure in cooling system:
As the coolant heats it expands hence pressure.
The radiator cap is supposed to handle some sort of pressure, replacing that can sometimes fix the problem.
If the pressure is massively undue then it is likely to be a headgasket.
The head and barrel needs to be skimmed. They are both ally and both warp.
Might be the cap yes, but this wasn't an issue a month ago, before I changed the piston, so I doubt it helps changing the cap - it's more likely the head that maybe is warped yes, I didn't really check it since it seemed to be in a very good condition.