Jon,I wish I could claim that it was due to my knowledge, wisdom and excellent riding skills, but the truth is that when I bought the bike (in 1983) it already had 35,000 miles on it.The previous owners must have really understood what they had there. I believe with a light right wrist those milage figures can be achieved by most riders. I think big bore kits really stress the whole shebang. If what I read is correct, the 500 are really bored out 350s. Thats quite an increase ,percentage wise, and it really sucks up the safety factor in the original 350 design. Much beyond that, and your in the "granny on dexis" mode.