Converting OMC prop for Mercruiser

carrier82

Petty Officer 2nd Class
Joined
Oct 1, 2013
Messages
118
Hi

I'm trying to install the SS prop from my old OMC Cobra sterndrive to my new SEI116 drive. After searching this forum I thought that and OMC prop could fit Alpha1 without problems. But that is not true. The center hub is too long and I can't secure the bolt using the Mercruiser "Borg ring" and there are no hole in the prop shaft to secure it using OMC prop hardware. Different thrust washers won't move the prop backwards enough and removing the thrust washer causes the prop to hit the outdrive casing (and still no enough splines to secure the prop). Anyone experienced with converting this type of a propeller to fit Alpha1? I'd like to use it in the future as well, because I think it's a fine prop. Although if the conversion involves too much labor, I might give up.

kuva1.jpg

kuva2.jpg
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,030
I have converted an Alpha prop to fit my Johnny 150HPV6 Outboard. I had to drill out some of the Merc's splines and then grind a Merc thrust washer to fit the taper of the Johnny's propshaft, and reuse the Merc Nylon Lock nut and spider washer. I would think it would work the other way, as you are trying.

Maybe a Prop shop could press in a Merc hub?
 

carrier82

Petty Officer 2nd Class
Joined
Oct 1, 2013
Messages
118
I have a press of my own and was planning to be cheap :) I might shorten the original hub. But unfortunately just changing the hub is not enough. What I wonder is the forward stopper on the rear of the propeller. Seen in the upper picture. That would restrict the nut from going in deep enough and I guess i'd have to cut it of as well. Now for doing that I may have no tools for.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
The easiest way to convert the prop is as follows

Sell OMC prop converting it to cash, then buy mercruiser prop ( converting cash to prop)
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,030
Those two motors would likely use the same prop but different hubs, if it were a modular type prop. It would therefore be a simple change, to swap modular hubs. I would recommend you visit a marine store and compare the two hubs. You will find that the OMC hub sticks out the front of the prop more than the Merc hub. I think all you really need to do is find a way (likely custom thrust hub) to get the prop located in the correct place on the prop shaft. Then you can sue some combo of Merc and OMC spacers and the Merc locknut and spider washer.

I had pretty good luck modifying a Merc thrust hub to locate the Merc prop on the OMC Propshaft properly. You may need two thrust hubs or something to adapt it.
 

carrier82

Petty Officer 2nd Class
Joined
Oct 1, 2013
Messages
118
Thanks everyone for input. I've come to a conclusion that grinding the rear cap off the prop is mandatory to convert that model to fit Merc. I'll take Admiral Scott Danforth's route.
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,235
have access to a "good" prop shop? its easily done by competent shop and lots cheaper than another prop......we've been doin' tha swap back n forth for years with tha big V6 stuff..........
 
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