I have an issue with a blade for my Murray 16.5 '42 lawn tractor. Currently, the blade hits the deflector assembly whenever the mower is placed in engage. When I replaced the old blade, the new blade continued to hit the deflector assembly. I also adjusted the blade rotation control to no avail. PLEASE HELP!:)

I would try a slightly shorter blade even if I had to cut a little off with a hacksaw, or try bending or trimming the deflector shield a little to get it out of the line of fire. Does it look like it is bent from striking against something maybe? Wear gloves the metal edges are sharp.

Are you sure the blades are hitting the deflector? Look at the deflector and see if there is markings from the blade. If so try adjusting the shape of the deflector.
DO NOT do as wildandblue suggested by cutting off the blades. #1, you could become injured; #2 you could cause severe damage to the mower due to the blades becoming out of balance damaging the jackshaft and bearings, and perhaps even the housing itself; #3 You could leave a streak right in the middle of each pass you mow.