Thanks Grumpy and wilco. I have cleaned up the surfaces of the engine and cover and will now purchase a gasket. I have fitted the cover back on loosely and the pull cord seems to be working reasonably freely with the only real resistance coming when the piston is at the top of its stroke. I have looked for a gasket on the Outdoorking website but there are so many. What is the exact name of this gasket? The engine is a B&S 3hp model 80202.