Usually its good practice to check During regular maintenance, if it seems to have a hesitation in its operation (piston) of the conrod, like play then its time to replace it. I have had motors last 3+ gallons on a rod, and others got replaced after a race meet. When in doubt, change it out! Running conditions etc. Can vary from person to person and motor to motor. Is it an ISON .21 7 port? What are you running it in?