How to fill 1968 3.9 hp lower unit oil

I know...stupid question, but the archives search function isn't working properly.

I picked up a 1968 Mercury 39 this summer. It had been completely dismantled and repainted (poorly) except for the lower unit. I've got everything back together except the lower unit. However, it is giving me the most trouble.

I'm trying to fill the lower unit oil, but I can't seem to figure it out. The lower unit is empty as the previous owner had a crack in the casing welded. There is only one hole at the top of the lower unit with a phillips screw in it. I assumed I would have to put the lower unit on its side and slowly squeeze oil into that hole while allowing it to vent. This didn't work. I can't get more than a few drops in and it is only at a drop at a time. Then I noticed a square top screw beside the shift rod. I removed it wondering if that would vent the lower unit. Of course, it didn't. Anyone have any experience with this machine that they'd like to share? Am I just not patient enough?

Thanks for any help.

Re: How to fill 1968 3.9 hp lower unit oil

Never worked on one. With the viscosity of gear lube, one would think that you have to have 2 holes for installation.

Sorry I can't help

Mark

Re: How to fill 1968 3.9 hp lower unit oil

Nevermind. I'm an idiot. I completely overlooked the HUGE vent screw at the bottom of the skeg. I promise to stick to OMC's after this one. lol

Re: How to fill 1968 3.9 hp lower unit oil

Glad you found it because you really had me baffled.......like there's gotta be a hole down there type thing.

Mark