i am not sure on the 250 but this is how it is on a 400ex. align the t-mark on the flywheel before you put your cam in. put the cam in(lobes facing down) and align the sprocket in the timing chain so that the two marks on the sprocket align with the top of the head. there is probally another line on the top of the sprocket telling you which side is the top of the sprocket and which side of the sprocket faces down. the compression stroke should not matter until you have the camshaft installed. i found it easiest for myself to align the t-mark first. then i put the sprocket onto the chain so that the two lines on the sprocket aligned with the top of the head. i then slid the cam through the cam sprocket. when your on the compression stroke, your exhaust valves will be loose, not tight. you should not have to hold the flywheel in place. it should stay there fairly well. with some effort, yes, it will move. good luck
2005 450r
*sold* 2001 400ex
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