Re: 150hp mercury outboard
I have a 90 hp with the 4.25" gearbox. Your's has the 4.50". My Merc Service Manual says put a 2x4 between the prop and the anti-vent plate and torque to 55 ft-lbs. You turn a 14+ dia prop and I turn a 13+ dia but I have run a 14+ on my engine so I guess the shafts are the same diameter. Therefore one would/should safely assume that 55 is the right number. If you want 60 put on 60....heck your torque wrench could be off that far. Basically they want it on good-en-tite.
Mark