Lower Unit Drama

[whughes]

I have a 2000 Mercury (made by Tohatsu) 5 HP 2 Cycle motor. I am trying to drop teh lower unit to change the impellor. When I first tried to drop teh lower unit I got it down a few inches or so and then realized I needed to disconnect the **** shaft. After disconnecting the shift shaft I was able to pull the lower unit about a foot down, but it won't come out any further, and it won't go back in.

Surely the drive shaft is down inside the main shaft, but what could it be binding on? I am using a Clydes manual along with a Tohatsu parts manual but I can't identify anything that would prevent the lower unit and drive shaft from coming out.

Any help or insight would be greatly appreciated.

Warren H.

 

[pvanv]

Re: Lower Unit Drama

There are three things that connect between the LU and the powerhead: the water tube, the shift shaft, and the driveshaft. They all have to separate in order to have the LU free of the rest of the motor. A decent Factory service manual should describe the procedure to drop the LU.

On some models, (what is your model?) the driveshaft is supported by a bushing inside the exhaust housing (think carrier bearing for a truck driveshaft). Keep in mind that the driveshaft operates in the filthy exhaust/seawater environment, and there can be an accumulation of crud on the shaft, which can present a challenge, since that accumulation can cause the shaft to not slide freely through the bushing.

 

[whughes]

Re: Lower Unit Drama

Thanks Paul,

I was just looking at the parts manual and noticed the driveshaft bushing assembly that is located in the exhaust housing, as you said.

Would the bushing assembly be attached to the exhaust housing to keep the drive shaft in alignment? And, should the drive shaft slide through the bushing without having to remove the bushing assembly?

You're right, it is pretty nasty inside there.

Cheers,

Warren H.

 

[pvanv]

Re: Lower Unit Drama

Warren,

On the Tohastu/Nissan brand (We're not a Merc shop), there are two bolts, oriented vertically, that hold the bushing assembly in place. I think they take a 10 mm socket. The bushing prevents any whipping of the shaft at higher speeds, but actually most motors will work OK without one.

Typically, we try to keep the bushing assembly in place and coax the shaft through it. It's usually nearly impossible to get a socket up there. In some cases, the bushing or its bracket can get damaged by the removal -- which can be a bear if there's a lot of accumulation on the shaft. Happens more on motors that are never tilted out of the water, and "live" in the down position. On some of these motors, it just takes a lot of patience, and a repeated "slide hammer effect" of pulling the LU down to scrape the crud off the shaft. Once the shaft is reasonably clean, it will pass through the bushing OK. Thereafter, annual disassembly is normally not a problem.

 

[whughes]

Re: Lower Unit Drama

Paul,

You were absolutely correct. The build up of exhaust gunk was causing the bushing to bind. The bushing assembly is located 6" or so from the bottom of the exhaust shaft and is secured with two philips-head screws. I was able to unscrew the assembly from the shaft and the lower unit and drive shaft came out. I cleaned all the gunk off the drive shaft and then removed the bushing, although it took some coaxing to remove it from the shaft.

So I'm back in business.

Many thanks for your help,

Warren H.