I am the third owner of an 03 WR450, and not knowing its history that well, I thought I would take the preventive measure of replacing the piston. It took me nearly two days from start to finish. I put over 2000 miles on the bike in the year I have owned it and I have no clue what the total mileage is. The old piston was actually in pretty good shape with little carbon build up. No scratches on the cylinder or piston. It was a great opportunity to learn a bunch about the bike, but in hindsight doing this the first time on my own may have been a bit risky. Thanks to the invaluable information I got from here it finally went back together and started. I did 40 miles of trails Sunday and the machine runs beautifully. Thanks again for letting me benefit from your experience and expertise.