nissan 15 lower unit

[tylerr83]

the 15 hp nissan on my duck boat was recently sucked some debris up into the water tube causing an overheat. after removing the cylinder head i cleaned the water jackets, checked the thermostat...etc...I also decided to replace the impeller since its been about two years, however, the lower unit would not drop down. shift linkage is disconnected and all bolts are removed. i thought that the drive shaft may have been frozen into the powerhead, so i pulled the powerhead...which came easily off the shaft. I've tried tapping on the lower unit with a deadblow mallet and with a 3lb hammer and block of wood but it will not budge at all. am i safe to try removing it with some heat or is there another better option?

 

[pvanv]

Re: nissan 15 lower unit

What is your model? The 4-strokes have a nut at the leading point of the LU that is sometimes overlooked.

If you have the powerhead off, the splines are not holding it together. You may have overlooked a bolt (or that forward nut). Heat would be a bad idea. The LU just mates up to the face of the driveshaft housing. Unless, of course, there is a lot of salt crud built up in the WP area of the driveshaft housing.

Does it drop down a little? If so, wedges are often used when the splines are too snug to let go... But in your case, that's not the problem.

 

[tylerr83]

Re: nissan 15 lower unit

i understand that its obviously not frozen into the powerhead....otherwise the powerhead would not have come free so easily, and with the powerhead being off now, there is nothing there to be holding it. I'm pretty certain that the studs from the midsection that hold the lower unit on are corroded from use in salt water. The nuts came free without too much trouble, but the lower unit does not drop down at all. I dont see how i could have missed a nut or bolt holding it on. There were two on either side of the cavitation plate....nothing in the front or rear, nor from the top as i had read others had found.

 

[TOHATSU GURU]

Re: nissan 15 lower unit

With the power head off, flip the engine upside down and hang it until it drops apart...Make sure you are only 1/4 inch off the floor.

 

[RCObill1]

Re: nissan 15 lower unit

I had the same problem with a 1992 NS15B2 two stroke, the 4 nuts holding it on came right off but the studs were corroded in the lower end and it would not move.. Tried several corrosion busters and nothing worked, what did work was a 1/4 x 4 inch wide flat steel bar and a air driven impact hammer. The steel bar was placed at the back of the lower end unit on the top, a strong structural point. The impact hammer was not a hard blow but several hundred rapid blows to break up the corrosion. Took about 30 seconds and it came right off..

Good luck