alright there, just got a second hand rb-x.12, seems to have good compression and holds its own weight sideways with ease, does anyone have one of these are they any good? and how do i check if the engine is in good condition, is ther anything i can look for if i take the backplate off? thanks for the help

The RB X12 is a decent motor if your track is on the small side. Otherwise purchase another motor to race and just use the RB as the practice/spare engine. Should you choose not to enter races then it will do just fine. First inspect the compression by turning the flywheel by hand and see if it has any pinch and or it shouldn't turn over so easy. Make sure you have a glow plug in there while doing this. Take the motor apart as well to inspect the internals.