Hi, sorry for the late reply. I have a 2008 crf450r, bought it used, running, started 1-2 kick, cold or warm, its a mx bike, but I doubt it was raced because the last owner rode it for 10hours, it had worn grips and a broken holeshot device. Don't know about previous maintenance. I've ridden it for 40h, and have only changed oils, filter and cleaned the air filter, no engine work. I also had it underwater once for 5-10 min, about cylinder deep, no water got in the airbox, rode it straight home for 10-15 min after that and changed oils, filter. That was approx. 30h ago. about 5 h before the "knocking" sound, it begin to start 3-5 kick, when I checked the valve clearance(now, when the knocking sound started): Exhaust. 0.29mm(left) and 0.33mm(right), Intake. 0.03mm didn't fit in, neither left or right, so 0.0 I'm guessing. Im certain I checked the clearances right (did it like 20 times).
pics,
https://i.imgur.com/3vkGeca.jpg ,
https://i.imgur.com/P1WO9mv.jpg
The chain tensioner doesn't move left/right, up/down, so I would assume its not broken in the housing. It moves out by itself.
When I take a look at the cam chain, I can visually see that its not tight. So a new question, could i have done any harm to the bike because the chain is worn. e.g the valves hit the piston etc.
A question about the valves, what do I need, if i have 1.2mm shims (the smallest as I've googled) and its at 0 clearance, do I need a new head, valves? what do i need to do?
And now something that's probably dumb as ., could I add washers under the cam chain holder thing, like 0.2mm thick washers, as I see that would raise the cam, and eliminate the 0mm valve clearance issue. BUT, the cam chain would be tighter, i doubt what would be a issue, because I lift it so little. But, I think the part where the valves meet the head (idk what its called) is already worn, and the washers would be a not-so-worth-it fix. Am I wrong?
Sorry for complicated explanation and bad english.