Stuart, as I told you previously, the Briggs and Stratton engine relies on the thickness of the crankcase cover gasket to set the end-clearance of the crankshaft. First, you should not have taken the crankcase cover off in the first place - all of your problems since have stemmed from that mistake. Second, it is not unusual for gaskets to be ruined when you dismantle an engine - when it happens, you have to fit new gaskets. Your crankshaft is jammed because of the absence of the gasket which provides its end clearance. Buy a gasket and fit it properly. I suggest you do not ever go back to that mower shop: it appears the person who advised you has probably never dismantled a mower engine, since most of them rely on that gasket to set crankshaft end clearance. There is nothing wrong with him not knowing anything about mower engines, but there is definitely something wrong with him giving stupid advice to a customer when he is consulted as a professional. The people serving at the counter in mower shops usually know nothing about mower engines, but normally they have enough sense to refrain from giving advice on the subject. They have a mechanic in the back room who (hopefully) knows about engines, but his time is worth too much to have him waste it talking to customers.
