I have a snapper 30128BE r.e.r. My nephew put together from mixed parts. The 12 hp B&S motor came off a sears LM. It's done well for me for 3 seasons. It started to have trouble climbing hills. Now it makes a grinding noise especially when I mash the clutch. There is no more nuetral anymore. When this started I replaced the drive wheel, the one with the rubber ring, and the gasket material clutch, but that didn't help. So I'm looking at it. The drive wheel has moved dead center to the horizonal plate that is mounted on the engine crank.What is supposed to hold that stationary? There is a yoke with a slotted opening assumed to be for ajustment. But mine has no nut, or locking mechanism. Is it supposed too? The grinding is worse when I try to put it in reverse. What is the problem? and how can I fix it?