Marine propellers must work all the time in all conditions. They can strike objects and bend, twist, chip and break completely off the drive shaft. Some propellers wear from age and thin out, causing annoying vibrations. Replacing a propeller involves many factors according to its design, pitch and material construction. Changing out the propeller also requires some precaution and forethought.
Remove the boat from the water. Place the boat engine in neutral with the key in the "Off" position, or remove it completely to prevent accidental engine start. Spray penetrating oil on the propeller shaft lock nut. Bend the castellated nut tab in the open position with a pair of pliers. If a cotter pin is used, splay its ends open. Cut the cotter pin ends with wire cutters and pull the cotter pin through the shaft nut.
Place the correct socket on the end of the prop shaft nut and turn it counterclockwise until it loosens. Remove it and lay it down face up, noting that that side will mount toward the front of the engine. Pull the locking tab ring off, if so equipped. Remove the spacer washer by hand and place it face-up. Make note of any additional washers on the shaft and place them in order.
Pull the propeller free of the spline shaft toward you. If the propeller seems stuck, tap the back of the hub with a plastic hammer until it comes loose. Pull the propeller off the shaft. Note how many spacers remain on the shaft on the outside of the thrust washer. Pull them off and place them in order. Remove the thrust washer and examine it for damage; flat spots, pitting or deformity.
Take your propeller to a marine supply store and have it matched up. You need to consider the blade pitch, metal material, number of blades and shaft diameter. Purchase a replacement thrust washer if you need one, along with a new locking tab ring or cotter pin. The new propeller should be made of the same material as the old one.
Use a wire brush to clean the shaft splines. Scrub parallel with the spline grooves, not against them. Wipe with a rag. Apply a liberal amount of marine grease to the spline grooves on the shaft. Replace the thrust washer and any spacers that followed behind it. Align the new propeller up with the spline grooves and push it on firmly until it seats.
Place the spacer washers on the shaft in the order you took them off. Place the metal tab ring on the shaft, if so equipped. Run the castellated nut onto the threads and snug-tighten it only. Refer to your owner's manual for the correct torque pressure and use a torque wrench to tighten it. It should be around 55 ft-lbs for the Evinrude motor.
Bend the metal tab over the flat end of the nut, locking it into position. For the cotter-pin design, run the cotter pin through the castellated nut and flair the ends with wire cutters. Spin the propeller by hand to make sure it rotates freely without hitting the cavitation plate.
