Chainsaw Repair

The 'trick' is to NEVER start the saw without a bar/chain on it right after installing the clutch.  Put a bar and chain on it and run it for a minute or so (with several 'revs') first.  That'll tighten the clutch tighter than you can with a wrench (without breaking anything).  Then you can safely run it with the bar/chain off if you really feel the need to do so....

That clutch can do serious damage to people and property when it comes off/apart.  I worked at an old shop with a high tin roof and tin walls.  There were several shrapnel holes in the roof and one wall over/next to one of the benches.   Years before I got there, some guy did the no-chain rev up thing after reinstalling a clutch.  He was seriously injured (along with the damage to the roof and wall)....