The clutch on a Ryobi Bc30 string trimmer sits at the front of the engine, where the boom shaft meets the engine housing. This clutch connects to the crankcase, so when the crankcase spins fast enough, the clutch also spins. This clutch uses centrifugal force to engage the clutch drum and driveshaft. So when the clutch spins fast enough to turn the driveshaft, the cutting head also will start spinning. Worn out clutch shoes, spring or clutch drum will cause the head to stop spinning properly.
Turn the Ryobi Bc30's engine upside down. Locate the throttle cable, which will be a metal cable or plastic tubing enclosing the metal cable, and will run from the carburettor to the throttle handle. Pinch the tabs on the end of the throttle cable where it attaches to the carburettor. Pull the throttle cable slowly away from the carburettor.
Unscrew the throttle handle cover, just above the ignition switch. Pull the two halves apart with the end of the screwdriver. Disconnect the short circuit wire from the ignition switch by using the flat tip of the screwdriver and your fingers.
Unscrew the four screws holding the boom shaft to the front of the engine housing. Slide the boom shaft gently away from the engine by pulling the shaft down while holding the engine.
Disconnect the rubber boot that's attached to the end of the spark plug. Undo the spark plug with the socket wrench and remove it from the engine. Insert about 3 inches of starter rope slowly into the hole where the spark plug was just located. This will block the piston from spinning so you can unscrew the clutch.
Unscrew the clamp holding the shroud in place over the clutch and starter assembly. Remove the shroud, spring and clutch drum from the front of the engine. Unscrew the clutch rotor assembly and remove the clutch rotor assembly and the washer underneath.
Clean and inspect all parts for damage. Replace any worn or broken parts. Install parts in reverse order: washer, clutch assembly, clutch drum, spring and shroud. Tighten down the clamp holding the shroud in place. Remove the starter rope from the cylinder and reattach the plug and boot wire. Reconnect the boom shaft to the engine housing. Reattach the trigger handle and throttle cable to the shaft and engine.
Do not put more starter rope into the cylinder than is needed. Putting in too much rope can damage the piston and the exhaust port.