we are having probs with the coolant on the shee every time we go out and ride the coolant level in the back reservoir drops to about 5 mm ,the bike runs great apart from that ,the guy at the bike shop said we mightv be losing it through the piston and might have to skim the head wat do u guys think............

 

This is how to check to see if the head is losing presure and causing the coolant to overflow, remove the radiator fill cap then start the bike and look inside at the coolant for air bubbles or alot of turbulance as when working properly the coolant should almost look motionless. Are you using a 50/50 mix of coolant and distilled water?

 

skim it, it'll fix you prob and you'll gain compression. . .
jus't don't take off too much unless you want to run higer octane