Re: Shear Pin for 1967 Chrysler 20HP?
The prop shaft is splined for positive prop drive and the prop hub has a rubber internal donut. The theory is that if you hit anything the rubber hub will absorb the shock---MAYBE--- Hit anything hard enough to have the rubber function and you will still bend the prop though
The drive or thrust pin only takes forward and reverse thrust loads and keeps the prop from sliding down the prop shaft and contacting the gearcase. it also keeps the prop from sliding off during reverse operation.
While I personally do not like this arrangement, especially on the big engines, I have a number of Chrysler engines from 8 to 125 HP that use these thrust pins and I have yet to see a pin shear. I have run props (well, my son and daughter did) into rocks and the prop was rather well bent but the pin was not even harmed. Another drawback to this system is that if you get some line (rope) or similar material wrapped behind the prop, it will force the prop against the pin so hard that you will need a punch and hammer to drive out the pin; you will not be able to clear the line or change the prop on the water.
The tailcone retains the thrust pin and it is held on with a cotter. If the tailcone is loose and the rattle bothers you, just insert a suitably sized O-Ring into it to take up the slack.