I put about 250 passes on mine before I go through it and that can be a couple seasons for me. Then it gets rings, bearings, wrist pins lifters and anything else that a close inspection reveals needs to be replaced. I check the heads and it gets new locks. I check the valve springs at least once a year and replace them as needed. If you run aluminum rods they typically need replaced at this time also. It really depends on how much power you make, how hard you rev it and what kind of parts you use.