Timing Advance Stihl 066 ms660 and many other Saws Step by Step How To 

I'm or harming the flywheel I'm only filing one side ive seen alot of saws sheer the key and ruin the Crankshaft too each there own

I thought the same exact thing. I always file the key, never even crossed my mind to do that to the flywheel. Also if you take a little ofg to much you're only out a few cents vs a 100+ or whatever the flywheel for that saw costs.