ops may have a more tighter tolerance at top dead center when new as far as breake in go to the engine wont run thread on the second page of the nitro engine zone i posted my brak in methed their, it works grat and that motor will last. the motor may need to be heated up quite a bit, if 200 to 220 dont do it then apply a little more, but once you get it going you will have to keep heat on it or it will lock up from cooling down. good luck