I do not have the manual for this mower. It's around an 1985, snapper hi-vac rider. I am replacing the engine and I do not know how to adjust the disk that goes on the engine shaft. This disk is above the rubber wheel that moves the rear tires. Should I have the trans. in neutral or in gear? Should I press the clutch pedal and then let the disk down? I had tried this and the mower almost took off in neutral. Any help??