the stock 21 engine in the inferno rtr does not have a key as i found out when fixing my friends buggy. I would put the sleeve in and put the cooling head on and when i would move the head for the screw holes the sleeve would move and be in the wrong area. I think the sleeve might of moved a bit when u put the head back on. have a quick look through the exaust port and see if the sleeve port is alligned correctly. and if not sure definately take it back apart and try and get it right. Make sure it is right cause u do nit want to damage or kill your engien.