RE: os fs 120 parts
check the valve that the rocker arm[broken] was on to make sure the valve is ok. to bend a push rod and break a rocker arm, something went wrong. i have four eng's, all are four stroke. nothing wrong with any of them. i only fly two of them. i have a spare rocker arm from a OS 1.20 surpass[parts eng] i can send you and you can see if it will fit. i quite flying two strokes back in the 80's. i'm an old fart, i started building and flying in 67 in SEA. kept me from going nuts.