Hi, for a reasonably competent mechanic it is very easy job to do. Turn mower on to its side with air filter/petrol tank cap staying uppermost. Undo centre bolt, remove blade friction disc and then broken part. The key may drop out, but simply sits back into the engine crank to stop the crank spinning inside the aluminium blade carrier.
Fit new blade carrier, ensure when on the crankshaft that it will not spin freely. If all okay replace friction disc & blade & tighten. Turn mower to correct operating position - Check oil level & restart
epark mowers
February 2009