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Outboard motor question


Alpo

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Don't know much about them, but I do know there is a piece down there in the prop called a shear pin. Its purpose, as I understand it, is if you were to get the blade caught on something, the shear pin would break, disconnecting the prop blade from drive, so you don't break either your prop or your motor.

 

Leave us suppose that you are removing your prop. Does the shear pin have to come off also?

 

A story. The protagonist picked up some line in his prop. Went over the side to attempt to cut it loose, but this was unsuccessful. Removed the prop to clear the line. It mentions him being careful not to drop the nut. It mentions having both the knife he tried to cut the rope with and the wrench he removed not with lanyarded to his body so they would not go diving. Even mentions throwing a line around one of the prop blades so it doesn't take a dive.

 

And I just thought of the shear pin.

 

Is it installed in the prop, so that when putting the prop on and off it comes with it, and you can't lose it? Or is it a separate piece, so you would (maybe) remove the nut, remove the pin, and then remove the prop?

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You remove the prop to access the pin. It is designed to fail so more expensive parts are not ruined. Remove prop and pin and replace. See Youtube.

Years ago my brothers and I had access to a small boat and motor and water skis. The rig was too small to ski with, but hey, we were kids. We bought the first pin as a single, but had so many failures, we bought a bag of them so we could continue to have fun. :lol:

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Some pins are under the prop nut & som are behind the prop.

                                                                                                                         Largo

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Shear pins are enclosed in such a manner that they don't slip out.

They're designed to "Shear" at a breaking strength much lower that the prop or gearing in the shaft of the motor.

A bother to replace, but a lot less expensive than the slip method that replaced the shear pin in some(??) motors.

The slip stops the prop from spinning when it hits a rock etc, then re-engages to hit the rocks again. And Again. And Again.

Before you can shut down.

To find the blades chewed off the prop.

Ask me how I know.

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And just because there is a  shear pin it doesn't mean the prop is saved from damage. Saving the engine and transmission are the reason for the shear pin.

 

Guess how I know.... :rolleyes:

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Shear pins are pretty much old school nowdays. Most of the props have a rubber sleeve that actually will slip when the prop hits something. The problem is that you can't replace it when it wears out, it must be sent to a shop that specializes in propeller repair.

 

Fishing line usually doesn't damage a prop. It gets behind the prop and damages the lower unit prop shaft seal. Then you get water in the gearcase and oil leaks.

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20 minutes ago, Big Sage, SASS #49891 Life said:

Shear pins are pretty much old school nowdays. Most of the props have a rubber sleeve that actually will slip when the prop hits something. The problem is that you can't replace it when it wears out, it must be sent to a shop that specializes in propeller repair.

 

Fishing line usually doesn't damage a prop. It gets behind the prop and damages the lower unit prop shaft seal. Then you get water in the gearcase and oil leaks.

The internet has saved us that step.  I just ordered a new hub for $40.  It will be a 10 minute job in a home press with some blocks and cut thick wall tubing for a spacer.  About $160 less than Mercury wanted for a new prop.

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Are the prop and the prop nut non-ferrous -- brass or bronze or something like that -- so they don't rust from being in the water all the time?

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Economical props are normally cast aluminum.  High end props are stainless steel.  There are some polymer options.  The splined shaft is factory coated with anti seize.  Just pulled off a prop that was factory installed 20 years ago.  It slid off like butter.

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I bought a boat from a San Diego fire fighter years ago and found out he had bought a new Boston Whaler to replace the boat he sold me, I saw in the paper a couple years later that he had been fishing tuna off San Diego and had hit something and destroyed the prop, In the process of putting the spare prop on he dropped it ( No safety cord) so he drifted for a couple weeks before he was picked up off the coast of Mexico. I have a safety cord pre- attached to my spare prop on my current boat.

No Shear pins on my outboards but I do carry spare nuts washers and cotter pins and everything else I can think of, I have no urge to take an extended float trip off Baja.

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Back in the 60s, dad had a 10hp Johnson.  The prop was held on with a brass nut molded into a plastic cover that was further secured with a cotter pin.  Take the cotter pin out, unscrew the nut (don't lose it), the prop slides off.  Under the prop is the shear pin going through the prop shaft.  After you shear one, you start carrying spares.  I know this.  Shearing the pin does not mean damage is done to the prop but it saves the gears in the lower unit.

Later motors started to use a slip disc of sorts.  Haven't kept up with it.

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