im am rebuilding my yz400f 99 and im up 2 the timming chain ( this is my first bike motor) how presice are the timing marks. with the bottom lined up to the i mark i can see both dots on the exhaust cam and 1 on the intake but it is only out by a flyshit (1 to 2mm) and it would be perfect. could the timing chain be a little streached? i know i should have put in a new one but i didnt. when i set the cams up perfect the i mark is out about 2 to 3mm off. or is that 1 tooth out on the bottom?