Too many, all depends on previous use and how the owner treated it. I gave a 20 year old Honda 25 to a family member, it needed a new gasket in one spot, that was it. When the mechanic looked at the internals, he told me it looked like new, no wear on the cams or valves, 100% compression. I used the Amsoil synthetic and that motor probably had 2000 hours on it. I'm not one to start a motor and immediately try to go warp speed, let things warm up a bit and go moderately before cruising.