So I took the 6 HP all apart, replaced the impeller, put the gear case housing back on , all shifts fine ------ until I put the powerhead on. With the powerhead on I can't shift into forward ---- the upper shift cam hits on the front of the powerhead-----and must be out of alignment now???? I have no idea how that might have happened and I cant find a picture of what it is supposed to look like ------ I never disassembled in the first place! Any thoughts????