I got my 2006 VS650 with 9k miles on the odo.
I checked the clearance around 25k miles, and they were all within spec.
The bike has 42k miles on it now, will check them again maybe this summer.
It would be interesting to see if anyone checks them every 4000 miles like the schedule calls for, and kept careful records for which way they wear (if they get tighter or looser) and how long it takes for them to get out of spec.
There are two wear mechanisms going on with an overhead cam:
1. the valve wears against the face seal on the head, which will reduce the clearance, making it tighter.
2. the rocker arm wears against the cam lobes, which will increase the clearance, making it looser.
Interestingly, if the valve face wears and makes it tighter, the rocker arm contact to the cam would have pressure on it all the way around the cam, which would tend to make it wear faster and loosen up again...
so the two tend to cancel each other out, if the wear is the same on both metal to metal contact areas.
If it tends to wear to the loose side, the tappets will get noisy, but until it gets really loose it wont hurt anything, you just lose a bit of valve opening.
If it wears tighter eventually the valves will not close all the way, and the hot gasses will blown thru the exhaust valve burning it, and the intake valve will backfire into the carbs - both are not good. The odd thing is the tappets will quiet down when they are too tight, which sounds 'better', but its a negative indicator of trouble. A quiet air cooled engine without hydraulic lifters is an engine that needs adjusting.
Tappets gonna tap.
Last edited by KCW; 05-18-2019 at 09:51 AM.