Um 4cyl sport bikes run at like 3-5x the rpm as old iron blocks. Which is something to think about. My CBR600F4 had 44K miles when I sold it last year, but it was still running smoothly. My 2007 R6 has 16K miles on it but things are swell with that bike too. I changed the plugs and adjusted the valves recently but that cost was minimal $600. A high miles bike should require some suspension rebuilding or maintenance to keep things smooth.
My buddy has a Honda 929RR that had 60k miles on it before it got wrecked. It needed a timing chain pretty much, but luckily a bicyclist crashed in to it before that got dealt with.
$600 for plugs and a valve adjustment! Did you have to send the bike to Japan or what?
So it's safe to say the average rider could drive one for 50 to 70k without it throwing a rod, would that be fair?
