Removing the clutch on a Stihl chainsaw requires a few speciality tools that can be purchased only from a Stihl service dealer. These tools will allow you to remove all the clutch parts without damaging them or the engine. These tools, while somewhat difficult to find, will be far less than the cost of replacing a crankshaft, flywheel or the entire clutch.
Piston Locking Strip
The clutch is attached directly to the crankshaft. To remove the clutch, you must prevent the crankshaft from spinning. For this, you will need a thin rubber tool that is inserted into the cylinder, where the spark plug sits, to block the piston from moving up and down. While some may recommend using some of your starter rope, this can be dangerous if done improperly as you may insert the rope too far into the cylinder. The rope will then exit out the exhaust port and may get stuck, ripped off and melt, ruining the cylinder and exhaust port. The rubber tool cannot be inserted too far.
For most Stihl chainsaw models you can use a standard socket wrench set with a 19mm attachment nut. This will give enough clearance to keep the handle of the socket wrench from hitting the walls of the engine. This nut is a left-hand thread and must be turned clockwise to loosen and counterclockwise to tighten. If the bolt gets stuck or you cannot free it, do not use a punch or other device as you may miss and damage the crankshaft stub. If you cannot free it, spray a little lubricant onto the stub and let it sink down into the nut.
The three clutch springs are attached to posts inside the clutch assembly. To bend these hooks so they slide off their posts, use the metal hook manufactured by Stihl. In a pinch, you may be able to use an old coat hanger or similar device with a flat screwdriver. Remember these springs can pop out unexpectedly, so wear safety glasses and keep all people and pets clear while you remove and install these springs.
Once you've removed the clutch, clean and carefully inspect each part for damage. The clutch shoes and clutch drum need to maintain a specific thickness to function properly. Also lubricate the needle cage with a multipurpose engine lubricant before reinstalling it into the sprocket. Always check the function of the clutch before restarting the chainsaw, as an improperly installed clutch can fly off and cause injury.