4 hp Johnson water pump

I am trying to replace the wat

I am trying to replace the water pump on my 94 4hp Johnson. The shaft from the engine has a flat spot on it for a nylon key. How do I slide the lower unit on the shaft with this key in place? The key is what turns the impeller. Do I need to take the engine off and if so how? Hope you can help

I'm sorry but I do not und

I'm sorry but I do not understand. The shaft should be installed in the lower unit then installed back into the shaft housing into the engine unless this engine is something that I have not seen before. Is the pump located in the top of the lower unit? If so slide the impeller down on the shaft with the key inplace then slide the pump housing over the impeller turning the shaft clock wise as you lower it over the impeller. Be sure to put a little grease in the pump housing where the impeller makes contact. This will keep it from burning when you first start the engine. Hope this helps.