yes.. it is normal.. if you are that worried take the backplate off and check that piston is fully seated on the pin.. i take my new engines apart when i take them out of the box only because when i got my os .50, i ran it then the next tank it wouldnt run at all. and when i took it apart, there was a length of fuel tubing all chewed up thruout the motor which killed the glow plug.. but most motors are notchy at top dead center....