Stihl 261cm, I need some help!

[huskydave]

Working on the key.

ok doesn't look bad, make sure the flywheel bore and the crank stub are clean, no dirt or oil. You want this to be a dry fit so it locks on good. When you install the flywheel give it a good shove so it locks on the taper well, then tighten the nut good. Set the coil gap to 10 thousandths, 2 sheets of paper will work or a business card. place that on the flywheel, loosen the nuts on the coil, push down very lightly and re tighten and pull the paper out. if you have rust on the flywheel magnets or coil use emery paper or such and sand the rust off. It will make a nice blue spark this way.

 

[PV Hiker]

Emery cloth to clean the matting surfaces.

 

[leaf]

Key isn't absolutely necessary. Make (small, exact) marks on the "outside" of the flywheel for exactly correct rotational position. Place flywheel, and tighten flywheel nut at first "gently" and then tighter until flywheel held in exactly correct rotational position and tight on the taper of the crankshaft end. (It is the taper"' that holds the flywheel; the key just lines it up, really.)
Other relevant activities can include printing out a "degree wheel" (from the internet), sticking it onto an old CD. Observing timing as you install flywheel, etc. Top dead center can be observed with a dial indicator, but lots of people are pretty good with a metal pin, etc.