Re: 1955 25hp Evinrude Tilt won't lock when up.
That's because there isn't a lock in the up position. I used a block of wood to hold the motor up. For trailering, use the block of wood in conjunction with tying the motor down to prevent the block from falling out.
Short term, another option is to tighten the tilt bolt nut on the clamp brackets. It has a spring washer under it to add tension to the tilt so that it will stay where you put it. Will only work at rest or in neutral - will not hold the motor up while underway.