Drive shaft on 1996 120 HP Force by Mercury Marine

[router343]

I have a 1996 120 HP Force. It currently has the extra long shaft with the "5 spacer. It sits to low in the water on pontoon. Can I replace the "25 inch shaft with the "20 in shaft? From what I see it is just a matter of removing the spacer and replacing the studs with shorter ones and remove the shaft install shorter one and put it back together. But is there more involved that what I am seeing?

 

[Frank Acampora]

You have most of it--don't forget the water tube. The only caution is : I don't remember if that engine uses a 2 piece drive shaft. If it does, you are gold. If it does not, you would be best looking for a whole used lower unit. Unless you have an engine junk yard near you, finding the shorter drive shaft for a 2 piece shaft may be difficult and you may need to buy new. THAT will be a pricey proposition. Before you start, be certain what drive shaft you have and/or find the shorter drive shaft if it is a 2 piece.

 

[router343]

Thanks for the info Frank. I have had the lower unit off before and it is a one piece shaft. I was hoping for quick fix.Looks like I will just keep it the way it is and just look for a used transom that doesn't have the notch cut out of it so i can set the motor higher. I do have one more question, on a pontoon boat should the cavitation plate be just below the motor transom or the bottom of the pontoon. I have a lot of water s[lashing up back there.

 

[Frank Acampora]

If you have a notched transom, you can raise it by mating in a couple of pieces of good marine plywood to proper thickness and plating both sides with some heavy gauge aircraft grade aluminum.---NOT diamond plate. It is too soft for this application. When running, the anti-ventilation plate should be at the water surface or very slightly below it. I can't give you a reference as to where on the pontoon it should be because I have never run a 'toon and don't know at what depth the transom well sits.

HOWEVER: If the A/V plate sits too low in the water, impact will force water to ride up the leg and over the transom splashing into the splash well.