built a gx390 cart motor back in 2014 and ended up clearancing the crankcase with a dremel at 3am bc the billet rod was smacking the dipstick tube and cam lobe. classic rookie mistake. you gotta dry fit and rotate the crank by hand multiple times before torquing the side cover down or you will grenade your build in 2 seconds flat. stripped out an arp rod bolt once cause my torque wrench was uncalibrated junk too. check your clearances