1975 9.9HP and 1976 15Hp Lower Unit Interchange

[OptsyEagle]

I own both of the motors above and have decided to take the powerhead from the '76 15Hp and put it on the mid-section of the '75 9.9Hp since my 15HP has some useless motor mounts. The head bobs around quite a lot and the 9.9Hp seems to be fine. I don't want to pay the very high price to replace the motor mounts and I happen to have this parts motor that I could possibly use to replace them.

I also thought I would use the lower unit of the 9.9Hp motor since the 15Hp has a little more corrosion on it. It works fine but the 9.9Hp looks a little better. When I looked at the parts diagrams for both motors I noticed that the gearcase casings and the mid-section housings are identical part numbers, but the drive shafts have different part numbers. I also noticed that the two respective motors have different part numbers for their pinion gears.

I guess my question is, does anyone know if I would be able to take the lower unit of a 1975 9.9Hp motor and shove it up into the powerhead of a 1976 15Hp motor. I am thinking that maybe the reason OMC uses a different part number for the drive shafts is for a change in the end that goes into the pinion gears and if I am using the entire gearcase, this may not matter, in my situation.

Has anyone done this or encountered this issue or have any thoughts at all?

 

[kbait]

Lower units will swap if both motors are long shafts, or if both motors are short shafts. Driveshaft to powerhead coupler splines are the same.

 

[OptsyEagle]

That's what I thought. I will look closely at them both but I have had both lower units off the motors at different times and I did not notice any difference then.

I thought I would ask because everytime I shove a lower unit back up into a midsection/powerhead it always seems, for a while, that it is just not going to fit and then with a small move of the flywheel or propeller, up she goes.

Thanks for the reply.