I took apart my MT300x too last night , take off the engine screws first , then unclip the wires connecting to the starter. Pull the engine out from the driveshaft. Take apart the trigger and thread the Throttle cable through. After its all be done , push motor back into place and reconnect wires. This is where your motor and shaft will get stuck , just turn the motor cyclinder untill it will fit in , remember, the driveshaft is square so it has to fit into the square hole. Once in place , screw in the engine bolts and your done!
Jack
July 2012