I have a couple of 66cc china girls. The first one I built has around 3000 miles and has been running RICH its entire life. When the season ends and snow falls, I will tear down the engine. I already have new rings to put in, but should I put a new piston in as well? It also has a really loud knock at idle so I think I will replace the wrist pin and needle bearing. I ordered bits to solder and rejet to a leaner setting. I'm also replacing all the hardware since all the screws are chewed up and I had a stud snap on the new bike. Any other matinence that anyone recommends? I won't change the cylinder or head as they are fine and I don't want to spend the money (I'm in high school). I will also retard the timing by filing the woodruff key to prevent 4 stroking=more stress. I want to shave the head a bit and port/ramp, but with this old of an engine I think I'll just baby it. It still can hit 34-35 despite the age and running way too rich. I'm hoping the rings will bring back some compression as my new bike hits 40-41 with the spark retard, porting, and ramping. All stock parts. Over the 3000 miles, I have only replaced the clutch cable as far as break downs go. Originally built to ride to work when I was only 14. Now my friend and I race around the neighborhoods and trails and we ride them HARD. I still use them for trips that are ~3 miles. Too much fun for how cheap they are. I find them very durable if you maintain them and build them right. However, if I build another, I am replacing all hardware before I build and re-tapping the mounting studs for 8mm.