How to replace a flywheel;
1. Remove the clutch starter recoil cover from the saw.
2. Remove the bar and chain from the saw.
3. Remove the top cover on the saw to expose the spark plug
4. Remove the spark plug
5. Get your self a piece of clean nylon cord about 12” long and stuff about 4” inches of it or so in to the cylinder through the spark plug hole. (make sure none of the rope works it’s way out through your exhaust port, otherwise you’ll have little bits of cord to clean out of your cylinder).
6. Find the right sized socket to fit the flywheel nut, usually something like 13, 14 or 16m on European saws, or ½ 9/16 or 5/8 on older American saws.
7. Loosen the nut by turning it to the left, the flywheel nut is regular thread.
FAINT OF HEART TURN BACK NOW… THIS IS WHERE THE PROCEDURE BECOMES DICEY AND IS NOT RECOMMENDED FOR THE ANAL OR PEOPLE PARANOID ABOUT ‘WARPING FLYWHEELS’. I’VE PERSONALLY REMOVED SEVERAL THOUSAND FLYWHEELS THISWAY WITH NO NEGATIVE REPROCUSSIONS.
8. Unscrew the nut until the top edge of the nut is flush with the end of the crankshaft.
9. Pickup the saw powerhead by holding onto the sides of the flywheel.
10. Hit the flywheel nut (which is flush with the end of the crankshaft to protect the crank threads) with quick, sharp blows of a small ball peen hammer.
11. When the flywheel pops off put the saw down and finish unscrewing the flywheel nut.
12. The flywheel should be loose and come right off now.

If you find it impossible to hold the saw up by the flywheel you can use a small pry bar or broad, flathead screw driver behind the flywheel to apply pressure but you run the risk of damaging other parts on your saw like the cylinder or case with the prybar.

Installation:
1. Place the flywheel on the crankshaft.
2. Align the flywheel keyway with the flywheel key.
3. Tighten the flywheel nut