Hello , I built a small little extra-10 3-D plane and it called for a 15 size engine. So I put a OS 15 LA on it and its not enough power for me, So then I got a new OS 15cv-a And my question is this new 15 cv at top dead center the crank shaft moves a little bit and the piston does not. Like a 1/8 to 1/4 of an inch with out the piston moving ! Is this nomal and just needs broke in? The 15LA does not do this. Maybe its a bad engine? Doesn,t OS start and run all there engines before they sell them ? Any one heard of this before ?