Mercury 1983 18HP lower unit on a 1996 25HP - Will it work and should I do it?

gjryans

Recruit
Joined
May 3, 2010
Messages
4
Hey all,

I have a barn find 1996 Merc 25HP SN 0G342150 that has a destroyed lower unit. I got hold of a 1983 lower unit knowing there were some differences, but willing to take the risk because it is a nice solid unit that I got ridiculously cheap. So far, the only differences I have ran into that affect fit-up are the shift shaft and the 4 housing bolt holes are too small. I was able to swap the shift shaft with the 1996 and I think it will work. The drive shaft length, hole patterns, etc. are all the same. My question is if anyone has any solid reasons of not boring out the four mounting holes so I can use this lower unit? Are there other major differences that will surprise me?

Couple side notes:

-I am going to put a full seal kit in the '83 lower unit and pressure check it and everything. If I could ever sell it for enough to buy a compatible newer lower for the '96, or find the right person to trade, I would do it. I just think the likeliness of me getting that to work out are slim to none. I refuse to pay $500+ for one because I know I can avoid it one way or another.
-My end goal is to bring the 1996 back to life and flip this unit. I have worked on many outboards and enjoy doing it. What are potential buyers going to think about buying a 1996 unit with a 1983 lower?

Thanks!
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
8,152
Take a mic to the 96 lower unit see how much aluminum is left around the bolt holes. Then see if you will have enough aluminum around the 1983 lower mounting holes to drill it out. What is wrong with the 96 lower?
 

gjryans

Recruit
Joined
May 3, 2010
Messages
4
There's plenty of material there to drill the holes out. Someone had to of ran it dry by the looks of the melted drive gear and everything inside. Everything was completely stuck and I finally gave up trying to get the carrier bearing out and cut the housing apart to salvage the drive shaft. It's too bad because the housing seemed to be good but I don't think there was any saving it.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
8,152
Drill them if there is enough material. The main difference between the 2 lower units is the bearing carrier and the tools to remove it. That and the size difference in the mounting bolts.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,438
Left hand thread on the carrier.-------When they jam from no oil they really tighten up the carrier.----Small atomic bomb required to loosen it.
 
Top