Re: Nissan 1992 40hp outboard motor
Normally, both F and R gears turn all the time. The clutch dog selects which gear drives the prop shaft. Moving the shifter to R lowers the cam in the LU, which forces the clutch dog into the R gear. If that's stuck, or if the push rod spring in the LU is damaged, or if the shifter linkage came apart (either at the rod coupler of up near the powerhead), you could stay in R when you don't want to. Tiller models have a steering tiller handle; Remote models are setup for wheel or stick steering, and have an RC box to operate the shift and throttle via cables.
Grab a Factory service manual, available from any dealer (including me), and you can work on it; otherwise, time for a trip to the dealer for service.