Tonik 50cc 4 stroke Chinese Scooter. I am trying to get to the piston because I beleive they need replacing. I cannot get the valve cover etc off. 1. I have undone the 4 x bolts securing the valve cover. 2. Then an hour later after trying to pull off realised there were two more (see pictures). But it still seems solid on and won't pull off. Any ideas?