If you went to the Harley Plant in York, Pa. they tell you that a Harley motor is designed to last a minimum of 100,000 miles..if you install bigger cams and pistons and such then it drops down to about 75% of that..Now with the newer Synthetic oils and such..changing oils regular it seems like 150,000 plus is the norm..I have a friend who has a dresser with over 200,000 on it and hasn't been touched yet! I change the oil in mine every 3,500 miles and i always let it sit and warm up till the heads are so hot you can't touch them for more than a couple seconds..