Briggs/Stratton motor wont start

I have a 31c707- 17.5 briggs motor rocker arm stud bolt hole in head stripped out. Had a 17.o briggs motor & put that head on the 17.5 from what youtube said i adjusted the valves 0.60 gor the intake & 0.10 for the exhaust. Its getting gas & has spark but it turns over but wont crank. So im kinda lost now. Any advice would greatly appreciated