1963 75hp Electric Shift Prop

[yorab]

Motor in signature. I've done some research on the forum and read that the 10X9 1/4 is a good prop for a good holeshot. I ordered the Michigan Wheel PJ-74 which cross references to the OMC part #379260.

I noticed that the hub is different than the hubs on my other props. I know that the hub has a smaller diameter, but I'm referring to machined grooves that run down through the hub. None of my other props have those. Also, I can't see any rubber behind the hub plate. Is this indeed a rubber hub prop that is meant to be used with a drive pin and not a shear pin? Thanks.

 

[Frank Acampora]

Re: 1963 75hp Electric Shift Prop

That prop is indeed a rubber hubbed prop for an OMC engine. These old style props had a relatively small rubber "donut" and the size (diameter) was only slightly larger than the bronze flange at the back of the prop. Thus, it is almost completely invisible. Most of these early props were sand cast and the inside of the prop was rough. The rubber depended partially upon this roughness to stay coupled to the casting.

I often wondered and never did find out what those two milled slots in the bronze hub were for.

However, is it the correct prop for your engine? That, I don't know. I can see that the bronze hub has two drilled holes in it for a thrust/shear pin but where on the shaft is your engine's shear pin located? Same location as this prop?

 

[yorab]

Re: 1963 75hp Electric Shift Prop

Thanks Frank A. The holes for the pin do line up with the hole in my prop shaft. I was just curious about those grooves. I guess the prop could have been made for multiple models that either utilize the pin or a model that utilizes a splined prop shaft. This is just a guess though.

I was also curious about the hub and you gave a great answer on that for me. From my limited understanding of props for early OMC models, there was one that utilized a non-rubberized hub that required a shear pin that was designed to shear under heavy loads, i.e., hitting an underwater object. This saved the motor. The other models used a rubberized hub that required a non-shearing drive pin. The hub absorbed the load in the case of hitting an obstruction. I just wanted to be sure that I wasn't using a non-rubberized hub with a non-shearing drive pin.