The Propshaft: What It is, What it Does, What You Can Do…

by Super User
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An often overlooked and neglected part of your boat motor is the propshaft.  Without proper care and maintenance, the pshaftpropshaft can cause a major headache.  The propshaft is the piece that connects the pinion bearings of the lower gearcase with the propeller.  The two propshaft seals act as covering around the shaft to keep water ane elements from entering the gearcase.  If these seals fail then you could be looking at costly repairs.

It is important to regularly maintain this part of your outboard.  Start when your boat is out of the water or on the trailer. Shift your motor into neutral, remove the key from the ignition, and pull the kill switch in order to prevent any catastrophic injuries.  Begin by getting eye-level with the prop and manually spinning it. If you see any wiggle to the prop as it’s spinning you can know right away that the shaft is bent and needs fixed asap. (Driving on a bent shaft is equivalent to driving a car with a wheel out of balance)

Next give the propeller a thorough inspection.  Make sure blades are on the same plane when you spin it, look for bent blades or big dings in the sides of the blades.  To further inspect the propshaft you will want to remove the propeller (a socket and a screwdriver should suffice). Spin off the nut and lock washer and then you should be able to slide the prop off the shaft.  Behind the propeller will be a thrust washer, you will want to slide this off as well but pay close attention to which was it was put on. You will want to wipe off the thrust washer and inspect for damage. If it looks like the washer has been spinning under the prop then that means the prop nut was not adequately tightened.  

The main goal with all of this is to keep everything lubricated and not damaged.  The prop shaft itself needs to be especially lubricated to avoid the propeller corroding itself to the shaft.  Apply the lubrication liberally as you re-assemble the pieces to the propeller, remembering to put the thrust washer back into place.  In addition to ensuring all the nuts are tightened securely, many service manuals suggest retightening the nut after you’ve run the outboard once and thrust has seated all parts.