Lower unit mysteries

I need some help/answers about a lower unit I recently acquired. It's off a 79 Merc 50 hp. Was hoping it would replace the LU on my 73 Merc 500, but am unsure. The round thing (bushing?) that surrounds the base of the shift shaft is different, it's flat with two grooves on the 79 LU...different than mine. Also the top of the drive shaft on the 79 is not tapered and has no spring nub on the tapered end. And finally, the water pump housing seems different...on the 79, the bottom half seems to be a metal casting? that looks like it isn't removable? Only the top half of the pump housing and impeller are the same as on my 73 Merc 500 (serial # 3,479,524). Don't know the serial number of the 79 motor. Will the 79 mate to my outboard leg all right? Do you remove the cast water pump housing (lower half) in the 79 when you rebuild the pump? Lots of Q's...but I am a curious George. Any answers appreciated.

Re: Lower unit mysteries

I don't know your motor so may not be of much help. Having said that my thoughts are to try it since you have both. The things that matter are the fit of the driveshaft, water pick-up tube and the gear shift rod (assuming the mounting bolts line up). The rest can look different, one from the other, but would not have an effect on the operation.<br /><br />Before I did much of this stuff I would hit the library to see if the gearing in the gearcase is the same.<br /><br />I would assume you have a reason to do this other than the one is on there is a 73 and the other is a 79.

Re: Lower unit mysteries

Thanks for the reply. Guess I'll try it on my outboard leg, if I can figure out the water pump. Anyone know if the bottom water pump housing on a 79 Merc 50 hp lower unit is replaceable? Appears to be a metal casting? How do you get it out to replace the water pump? Any ideas welcome.

Re: Lower unit mysteries

Hello! Go to http://www.pfs-ware.com/ click on johns old merc page. they will help you out!

Re: Lower unit mysteries

Been there, done that. But I'll try again. Anyone here know about water pump rebuilds on a 79 Merc 500? Any replies appreciated.