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1973 7.5 Mercury Outboard Water Pump

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  • 1973 7.5 Mercury Outboard Water Pump

    I have a 1973 Mercury 7.5 HP outboard that hasn't been run for many years.
    I started it recently and believe it or not it runs great, but no cooling. The paint on the power head is shiney so I don't believe the motor has many hours on it.
    I removed the lower unit and removed the water pump upper housing and the
    impeller blades were all broken off. The shaft is quite rusty and I am unable to remove the impeller hub. I would like to purchase the complete repair kit.
    How do I remove the lower pump housing to replace it? Any suggestions on how to free up and remove the impeller?
    Most local lakes are trolling motor only which may explain why this motor has not seen much use.
    Please help this old retired Chief. I have a few fishing years remaining.

  • #2
    Re: 1973 7.5 Mercury Outboard Water Pump

    you can soak it with lube and let it sit for a while. if that doesn't work then keep soaking it


    • #3
      Re: 1973 7.5 Mercury Outboard Water Pump

      I have soaked the impeller hub overnight, but I still can't remove it. The hub seems to be seized to the shaft. I assume that the impeller hub must be removed before the pump lower housing can be removed.
      When and if I am able to remove the hub and attempt to remove the lower pump housing, will the copper/brass tube that goes to the water inlet slide out of the water inlet cavity?
      Please, I need advice from experienced mechs that know tricks for overcoming
      these obstacles not covered in the manuals.
      P.S. I have been soaking the parts with WD-40. Any suggestions about better penetrating oils?


      • #4
        Re: 1973 7.5 Mercury Outboard Water Pump

        I'm having the same issue with my 1975 7.5HP. i managed to get the impeller out then just left the bottom of housing intact. Was only able to get base up 1/8" then stuck. Had an automotive mech recommend "PB Blaster" for penetrating oil but not real sure.


        • #5
          Re: 1973 7.5 Mercury Outboard Water Pump

          WD-40 is not the best penetrating oil. PB blaster/ kroil/ marvel mystery oil, you will much better luck.


          • #6
            Re: 1973 7.5 Mercury Outboard Water Pump

            I have been using Liquid Wrench penetrating oil, but have now purchased
            PB Blaster and a propane pencil torch for heating the hub. The rubber is all removed and the hub is bare metal, but I have no way to get under it to pry it. The hub is hexagon shaped and a 9/16" socket fits over it. I have held the hex socket with a vise grip and the shaft with another vise grip and tryed to wiggle it back and forth to break loose the key. So far no good, but I will continue to soak it with PB Blaster. Any additional suggestions will be appreciated.
            P.S. The lower housing is beyond use, so I am now committed to replace both the upper and lower housings.


            • #7
              Re: 1973 7.5 Mercury Outboard Water Pump

              can you post pictures of the parts you damnedge? (SP?)


              • #8
                Re: 1973 7.5 Mercury Outboard Water Pump

                Attached Files


                • #9
                  Re: 1973 7.5 Mercury Outboard Water Pump

                  Hmm my impeller wasn't like that. I caught the rubber underneath and pried up and it came up. The "key" is just laying in a groove. if you pull straight up, it should pull off. But that looks like a nut... I'm a tad bit confused. All the impellers I've seen have had a smooth cylindrical "hub" that just slides down the drive shaft into the lower housing.


                  • #10
                    Re: 1973 7.5 Mercury Outboard Water Pump

                    Don't mess around, just split what's left with a chisel. A small, thin chisel will get in there and do the job. What I've found works even better, if you care to make the tool, is to take an old flat-bladed screwdriver and grind the tip to a razor-sharp edge.

                    The very thin blade makes it easy to split the brass insert.

                    There are a couple of caveats to splitting the insert, but it's about the only way you're gonna get it outa there:

                    1) You can damage the impeller drive key if you end up splitting the insert right at the key. Kinda hard to tell 'cause it's not easy to see where it is. Keys are cheap.

                    2) You can damage the pump cup by driving the key or even the brass center of the impeller downwards into the cup. Cups aren't that expensive, either.

                    Besides, you're gonna renew those parts anyway, eh??

                    It is somewhat of a pain to pry the old stainless cup out of the lower pump body, you have to fold the sides inwards and keep working at it until it loosens up enough to come out.

                    If you were to buy the whole pump kit, it's a bit $$$ but would come with all those goodies already installed, and a new driveshaft oil seal at the bottom. If you're ambitious/adventurous/frugal, replace the seal/insert/etc, re-using the upper/lower pump halves (providing they're OK), and save some $$$.

                    HTH & Have Fun........ed

                    p.s. the I.D. of the brass impeller insert is smooth, the O.D. around which the rubber is molded to, is not. What you're seeing is the outside of the insert, stripped of the rubber. A lot easier to work on in that condition.


                    • #11
                      Re: 1973 7.5 Mercury Outboard Water Pump

                      Thanks Ed and others for your help.
                      Yesterday I managed to loosen the hub. A 9/16" 1/2" drive socket fits over the hub. I held the socket with a vise grips and the shaft with another vise grips, then rotated (wiggled) the shaft back and forth. The hub broke loose and I could feel movement (slack between the key and keyway).
                      Today I am going to get a duck bill Vise grip pliers so I can grip the hub and try to work it up the shaft. If that doesn't work I will go to plan B, (Ed's suggestion of using a sharp chissel). I do plan on purchasing a complete water pump kit. Thanks for all your help. I will keep you updated.


                      • #12
                        Re: 1973 7.5 Mercury Outboard Water Pump

                        Thank you, Thank you, Thank you to all!
                        Your suggestions and advice have paid off.
                        Attached are photos.
                        Thanks very much, you have all been a great help.
                        I will now order the Water pump kit.
                        God bless you all.
                        Your friend,
                        CPO Bob Basselgia USN (Ret.)
                        Attached Files


                        • #13
                          Re: 1973 7.5 Mercury Outboard Water Pump

                          I have edited my last post, removing my email address. I should have read the rules before I entered the forum. Sorry!


                          • #14
                            Re: 1973 7.5 Mercury Outboard Water Pump

                            I would have found the nearest not rate, told him what to do while I was drinking my black coffee. Told him I would help but I have an important meeting to go to. Then I would go fish off the shore someplace until the end of the day

                            That's the way I used to do it.

                            HTC Retired


                            • #15
                              Re: 1973 7.5 Mercury Outboard Water Pump

                              Good to hear from a you chief.
                              Problem is, I'm retired and all my non-rated have flown the coop, so now I drink my coffee and turn to and do it myself. The fishing part sounds good. I think thats what I will do until my parts arrive.