Nissan (NS9.9B2) 9.9 HP Lower Unit

I am attempting to drop the lower unit off of my 9.9 model # NS9.9B2 and am having a heck of a time. I removed the four mounting nuts from the under side and popped the pin out of the shift linkage, the unit will not budge and it seems as if it is fused to the shaft of the engine. I have tried to get a scraper, flat head screwdriver and even heated it with an on demand plumbers torch and hit it with a mallet, nothing.... Are there any suggestions? Is there a hidden nut? Do I need to heat it more? I am at wits end!

Odds are that the driveshaft is stuck in the crankshaft splines. Do not use heat. Use wedges and patience. If the driveshaft is twisted, it may be very difficult to get it apart. When reassembling, grease the splines.

Where does it actually seperate from ? If i am guessing right it seems like it seperates right above the mounting bolts. What is he best way to attemp to ge a wedge or screwdriver up in there? When i mentioned that it is fused shut it is fused shut. Doesnt look as if there is any gasket there and it seems as if anyhing the lower unit slides up into the middle shaft. Should i take a whiz wheel and cut a slice in the side to fit a flathead?

Here is a diagram of a similar unit. No gasket is used.

Thanks all who helped, I got it apart and heres how. I attacked the beast by roping the head unit to a tree and the lower unit to another tree with an electric winch. I put a resonable amount of tension on the cable and began to shock the lower unit with a rubber mallet. I then got a chisel in between the lower unit and middle unit where it fuses together. After a bit of messing around I was able to get a pry bar in between and then BAM! It gave out like a shotgun. No damage just a poorly maintained shaft spline with no grease. I will grease wll b4 re attaching. Any insight on other maintenance to do with lower unit apart?

Just the usual change of LU lube. Do a complete wp kit; not just the impeller. Beware that you will probably never find any carb parts for that motor, so maintain well what you have.

What are some neccessary steps to maintain the carb?

Just the usual... keep it clean... run it dry at the end of each and every day... don't damage anything on it.

alpar80 said:

I am attempting to drop the lower unit off of my 9.9 model # NS9.9B2 and am having a heck of a time. I removed the four mounting nuts from the under side and popped the pin out of the shift linkage, the unit will not budge and it seems as if it is fused to the shaft of the engine. I have tried to get a scraper, flat head screwdriver and even heated it with an on demand plumbers torch and hit it with a mallet, nothing.... Are there any suggestions? Is there a hidden nut? Do I need to heat it more? I am at wits end!

Click to expand...

I just went through the same problem--a Nissan 9.9 that was over 15 years old and had never been apart. The lower unit was copletely frozen. I undid the 4 nuts and the pin for the shift rod. Then I tried a wood chisel. screwdriver and stanley cutter blades and 5 lb hammer which started one side 1/8 inch. The problem was the studs were choked up with aluminum oxide--that white stuff. I used two 5-packs of stanley cutter blades---bashing them into the cracks and doubling them up when one would go in a bit. I took about two hours of bashing using the blades,a wood chisel which nI had to re-grind and a screwdriver before it finally came loose---showing three of the studs all white with alum-oxide. I made some bad-looking marks on the castings but a file will take care of them.