When exposure to the rigours of boating damages the tilt tube on a 125 HP Mercury outboard you have to replace it. The tilt tube acts as both the hinge on which the motor tilts and the support for the steering cable. The replacement process involves working with a crane, lubricants and an outboard motor-variation of "the old switcheroo," meaning you replace a part before the engine knows its gone. The project has a high potential for dinged fingers and damaged egos.
Press down on the latch handle at the rear of the motor cover, tilt the motor cover forward and lift the cover off the motor, exposing the lift ring on top of the motor. Move the shop crane to the motor--the motor weights 147 Kilogram, so a lifting device is essential--and insert the crane's hook into the motor's lifting ring.
Raise the motor just enough to relieve the strain on the motor's mounting bolts. Spray a substantial quantity of a moisture-excluding spray lubricant onto and into the tilt tube and wait for an hour, allowing the lubricant to break through the particulates and corrosion that might hold the tilt tube--or the steering cable that passes through it--in place.
Use a 9/16-inch socket and socket wrench to remove the nut that connects the steering link rod to the end of the steering cable. Pull the steering cable from the tilt tube. Place a length of metal pipe of the same outside diameter as the tilt tube against the port edge of the tilt tube--the end of the tilt tube nearest the left side of the boat.
Tap the end of the metal pipe with a hammer, so that the impact breaks the tilt tube free, causing it to move out of its hinge brackets. Grease the outside of the new tilt tube with marine grease. Insert the new tube into the hinge bracket on the port side and pull the old tube out while sliding the new tilt tube into place.
Apply a liberal coating of grease to the end of the steering cable, insert the cable through the tilt tube and reconnect the steering link rod to the end of the cable, tightening the 9/16-inch nut with the socket wrench.
Lower the crane's rig, allowing the motor mounting bolts to take the weight of the motor once again, but watch for problems with the new tilt tube. If none appear, lower the rig and remove the hook from the motor's lift ring.
Move the crane away from the motor. Replace the motor cover, front edge first, then lower the rear of the cover into place and re-engage the cover latch.
Determine the outside diameter of the tilt tube before you need to replace it and have a machine shop custom make a punch that size.
Always wear safety glasses when involved in heavy work around a boat. Keep your hands away from heavy, moving objects.