1969 Merc 7.5 hp Lower Unit Dis-assembly ???

[tpenfield]

Hi Gang,

I decided to start working on my old-ish 1969 Mercury 7.5 hp . . . It needs a whole new water pump along with a prop shaft bearing and new seals.

Right now I am 'trying' to get the retaining 'ring' nut off and am wondering it there are any tips/tricks to getting the 'nut' to break loose (goes clock-wise to loosen). I have the special tool for the retainer nut. My concern is getting a good enough grip on the LU housing so I can put a sufficient amount of torque to break the thing loose.

Last time I took the LU apart, a PO had already trashed the notches on the ring nut, so I ended up cutting the nut to remove it and replaced it with a new one. This time, I'd like to take it out intact.

I'm using my workmate bench as a clamp, but the LU is currently winning the fight.


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Any tips/tricks from the Mercury outboard experts :noidea: . . .

I just don't want to damage/crack the housing by putting too much force and not enough support in the right places. I already tried some mild heat, but that did not seem to work. I could get a torch to put some more heat on the housing . .

Salt water use, if that makes any difference.

FWIW - I've already 'invested' $$$ in this LU by replacing the carbon steel drive shaft with a SS shaft from a 1980-ish motor, so I'd like to be able to fix the pump, bearing, and seals to keep it alive.

 

[tpenfield]

I figured something out . . .

I had the idea of fighting torque with torque, so rather than clamping the LU the way I had it, I put it in the workmate so that it had more torque to resist the torque of the wrench.
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I was able to put enough torque with the breaker bar to get the ring nut to move.

Now I got to figure out if the bearing carrier is threaded in or just a press fit with the o-ring :noidea:

It's been a while since I've taken it apart.

TIA for any help on this. :thumb:

 

[tpenfield]

We the score at the end of the day . . .

Mercury Outboard = 1
Ted = 0

I was winning up until the final moments. I had the LU taken apart, replaced all the parts, new seals, water pump, etc. . . . all back together. Then came the water tank test. The engine would barely pump any water

Now I have the lower unit off . . . going through the pipe fittings, etc. Will check the impeller, but we will leave the score as is for the day. Hopeful to pull out a victory tomorrow.

 

[tpenfield]

Update . . .

I evened the score this morning. I found that I had missed a part of the water pump when assembling it - the top face plate :facepalm:

That is all back together and the lower unit is back on. Since the motor had been sitting for a year or 2, the fuel system is all messed up. So, that will take some work. Also have to order a new line that lead from the twist-lock connector to the fuel pump, since the original is cracked and spewing fuel.

The motor runs briefly, but will not stay running . . . funny thing was, yesterday the motor started right up and ran until I shut it down after a few minutes. I got to get some fresh fuel in it and a heavy dose on the fuel system cleaner. The plugs look OK

Hopefully, I will have this motor back in action by the end of the week. I've been wanting to fix this for a couple of years now to use on my dinghy/tender. The 3 hp Yammy (single cylinder) that is on there now is fine, but not quite the power or smoothness that the 7.5 has/had.

 

[tpenfield]

It's alive . . .

The old Merc 7.5 hp lives again. :thumb:


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I found that the engine would stay running at higher throttle settings . . . So, I started it in reverse and ran 3/4 of a gallon of a cocktail of new 2/3 2-cycle mix (50:1) and 1/3 seafoam. It took a couple of hours to run through the fuel, but that seemed to clean up the carb OK. I also cleaned the low speed air jet with acetone. Afterwards, I was able to set the idle mixture at idle and in gear. I drained the fuel tank and loaded it up with fresh fuel.

So, the Merc is back in business. I'll be trying it out in the next few days to see how it does on the water. :noidea:

 

[Scott Danforth]

congrats on the victory Ted.

 

[tpenfield]

Thanks, Scott. I'm really looking forward to over-powering my 8' dinghy with this thing. . . :thumb:

 

[tpenfield]

It works . . . :thumb:

I got the dinghy up on plane doing about 10 mph.


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So I will see how it goes for the balance of the boating season. Giving the Yammy 3 hp a rest now.