100k is about the norm for a chain. you bring it to me, and whether i know you and the car or not, i STRONGLY suggest at 100k, we pull the valve covers at EVERY oil change to check for chain stretch. at 6 degrees or less, look again at the next oil change. at 7 degrees or more, time for a chain, tensioner and rails. seen many a bent valve, never replaced pistons or a motor. good luck, chuck.