i have a 92 cbr 600 f2 and i drag race it. i changed the oil last summer with mobil 1 synthetic mc oil and ever since then ive had a tap or knock at an idle when its hot. it seems to go away when its at a rev or when its cold. i drained the syn. oil out and changed it with conventional mc oil and its still there. i think its the timing chain and ive been told its a valve. any ideas? and it doesnt have a manual timing chain tensioner.