Care Essentials About Outboard Propeller Shaft

While bad fuel and a dead battery remain the primary reasons, a modern outboard might leave you in the lurch, another area that deserves your frequent mechanical attention is the propeller shaft. The propeller shaft connects the pinion bearings of the lower gear case with the propeller. It's the one part of the outboard that makes the passage from the cozy, lube-drenched confines of the mechanical womb out into the harsh, unfriendly environment of air and water. The two propeller shaft seals act as a membrane around the shaft to keep water from entering the gear case. If these seals fail, it will cost you big bucks. Here's a simple propeller shaft inspection routine you can follow to help avoid seal failure.

Boating with a bent shaft is like driving with a wheel out of balance - it will put a lot of stress on those propeller shaft seals and on the bearings that support the shaft.

Next give the prop a quick inspection. See if the blades are in the same plane when you spin it, and check for bent blades or bad dings in the blades. A bent prop won't perform well, and will also spin out of balance, again putting undo stress on the shaft seals and bearings. You might feel this through the wheel or tiller, although hydraulic steering can mask this vibration. A good prop shop can repair minor blade damage.

Now you'll want to remove the propeller. You'll need a socket (a 1 1/16th-inch nut is the most common size on mid-size to V6 motors) and a screwdriver to do this job. Use the screwdriver to bend up the tabs on the lock washer that fits under the prop nut. Some other brands have a slightly different style lock nut, and some older motors use a cotter pin that you'll need to pull out with a pliers.

Your main goal here is to keep the prop shaft well-lubed so that the propeller does not corrode itself permanently to the shaft. Grease that thing up, drop on the thrust washer and prop, and using your wood scrap to hold the prop in place, tighten the nut. Which is tight if you don't have a torque wrench handy. If the lock-washer tabs don't line up with the slots on the hub, tighten the nut a little more - NEVER loosen the nut to make the lock tabs fit. The service manual suggests retightening the nut after you've run the outboard once and thrust has seated all the parts.

While that prop is off, you've also got a chance to inspect the outer seal, which is right behind the thrust washer. This area is always going to be greasy from the prop shaft lube, but if you see anything that looks like 90-weight gear lube, a seal could be leaking. Other signs of trouble might be a little dribble of lube on the ground below the gear case when the boat is parked for a while, or any signs of oil in the water around the motor. Of course, if the prop shaft is bent, it could be causing the seals to leak. 

So please pay more attention to your outboard propeller shaft!