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  • Mercury 1972 Thunderbolt 800 starting issue

    Hi everyone,

    I have a 1972 Mercury Thunderbolt 800 80 hp engine on my Mako 15. I just completed rebuilding the carbs because the engine has been harder and harder to start. The carbs are done and back on the boat. The last time I was out on the lake I tried to start the engine until the batteries died, they could no longer turn over the engine. I bought a battery charger from Walmart, a 10amp per hour, and charged the batteries 3 times over. I had removed the batteries to charge them. Tried to start the engine, but it barely turned over. Added my car battery to the mix with jumper cables, still barely turned over. So slow the engine will not start. I took the batteries to the auto shop and they tell me the tester says both batteries are good. I bought the boat used so I do not know how old the batteries are, but they are clean. There is no date on the batteries for age. All was fine with the batteries until I ran them down.

    So my question, maybe I need new batteries? Or maybe I having a starter motor issue? Maybe something else? I have had the boat in the water and running 12 times this summer. Hope to get it back out soon. Any ideas?

    Mark
    Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

  • #2
    I have a Merc 80 in my collection of oldies but goodies...one of my favorites!

    I would begin by pulling the plugs and see how she turns over without fighting against the compression.

    Things I've found as issues on the old Mercs:

    Top bearing on the starter will bind.

    Starter selinoid contacts develop resistance causing low volts to starter.(selinoid will be warm to the touch)

    Battery cables will sort of crystalize in the jacket causing high resistance, thus low volts at starter.

    Plug wires somehow got put on wrong plugs and causing bucking.

    And the craziest of all...no oil in lower unit allowed internals to rust causing a load on driveshaft, even in neutral.
    1992 211 w/175 OptiMax
    Glen Campbell, Pa.

    Comment


    • #3
      I'll try a cou of the things you have listed. I like the idea of pulling the plugs and see if I can turn the engine by hand. I will check the lower unit for fluid, though I have not had any issues with the it since the rebuild at the beginning of summer. I was told to check the voltage off the positive lead on the starter and ground while cranking over the engine, look for a voltage drop below 9.5. I can check the starter motor too, between the communitor and the stub, with an ohm of infinity. My plug wires are numbered, but I'll check them anyway. I may take the van's battery and see if it makes the engine turn over. Funny how all this started with low batteries at the lake!
      Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

      Comment


      • #4
        Hey Radioman, your list was right on. The top bearing was binding; I was able to loosen it back up. I also found the positive lead to the starter was a bit loose, which I am sure did not help. I checked the lower unit, the fluid is as blue as when I pumped it in early in the summer. No water or particles. I took the top cowl off and pulled the spark plugs, freed the top bearing bind, and now the engine turns over with one battery! It has not done that since I bought the boat in the spring.

        I noticed the teeth on the gear of the starter are becoming rather pointed. I'm thinking replacement this winter.
        Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

        Comment


        • #5
          Glad to hear some good news!

          You might want to check out these websites for some good info on keeping that oldie running...I've found quite a few used & new-in-box parts from the guys on John's site.

          http://johnsoldmercurysite.com/phpBB3/index.php

          http://aomci.org/forum/viewforum.php?f=2
          1992 211 w/175 OptiMax
          Glen Campbell, Pa.

          Comment


          • #6
            Great sites! I'll have to spend some time checking out the posts. My brother jokes that I have a new engine after all the work I have done on it. I am planning to paint it next spring, shine it up a bit. I am bummed I may have to buy a timing light again, I used to have 2 of them!
            Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

            Comment


            • #7
              Hi everyone,

              Quick update on my Merc 800. Brought it to the lake Saturday, engine almost started when the starter motor froze up. Came home and found a copper sleeve coming out of the top of the starter pushing the stater gear up so it would not release from the shaft gear. I wrenched the sleeve back into place, and brought the boat back to the lake on Sunday. Engine started this time (in less than 15 seconds). I tuned out the rebuilt carbs, and took off. Engine worked awesome! I have a new starter coming Wednesday. Once that is in, I should be set for a while with the engine, and since the lakes do not freeze in the Seattle area, I feel Cut Throat trout fishing coming!
              Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

              Comment


              • #8
                Hi everyone,

                Quick update on my Merc 800. Brought it to the lake Saturday, engine almost started when the starter motor froze up. Came home and found a copper sleeve coming out of the top of the starter pushing the stater gear up so it would not release from the shaft gear. I wrenched the sleeve back into place, and brought the boat back to the lake on Sunday. Engine started this time (in less than 15 seconds). I tuned out the rebuilt carbs, and took off. Engine worked awesome! I have a new starter coming Wednesday. Once that is in, I should be set for a while with the engine, and since the lakes do not freeze in the Seattle area, I feel Cut Throat trout fishing coming!
                Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

                Comment


                • #9
                  Your sure determined to get that old merc running well...., they were pretty good engines in their day...and as long as your patient and can get parts it should do you well...

                  BTW Merc made a slew of 3 cylinder 75-90 horse engines that are way more quiet and weigh far less....Wonderful little motors....

                  One may show up some day...[]

                  dave
                  [br]1994 Mako 215 Dual console Optimax 225[br]1978 Mako 19 with 90hp johnson[br]1996 Mako 22[br]1982 Mako 171 Angler 135 Black Max Mercury[br]1987 21b 225 Yamaha[br]1974 23 inboard Gusto gone.[br]1979m21 225johnson \"blue dolphin\" bought off this board and restored [br]with everyone\'s help!!Gone but not Forgotten....[br]1979 20 Mako 115 Suzuki gone[br]1977 19 Mako 115 Johnson gone[br]1976 23 Mako twin 140 Johnsons gone[br]1983 224 with closed transom and bracket[br]And 162 SOB (some other boats)[br]Venice Florida, Traverse city Mi.

                  Comment


                  • #10
                    Your sure determined to get that old merc running well...., they were pretty good engines in their day...and as long as your patient and can get parts it should do you well...

                    BTW Merc made a slew of 3 cylinder 75-90 horse engines that are way more quiet and weigh far less....Wonderful little motors....

                    One may show up some day...[]

                    dave
                    [br]1994 Mako 215 Dual console Optimax 225[br]1978 Mako 19 with 90hp johnson[br]1996 Mako 22[br]1982 Mako 171 Angler 135 Black Max Mercury[br]1987 21b 225 Yamaha[br]1974 23 inboard Gusto gone.[br]1979m21 225johnson \"blue dolphin\" bought off this board and restored [br]with everyone\'s help!!Gone but not Forgotten....[br]1979 20 Mako 115 Suzuki gone[br]1977 19 Mako 115 Johnson gone[br]1976 23 Mako twin 140 Johnsons gone[br]1983 224 with closed transom and bracket[br]And 162 SOB (some other boats)[br]Venice Florida, Traverse city Mi.

                    Comment


                    • #11
                      You know, after all the work on this thunderbolt 800, think I would enjoy rebuilding another engine. It has been quite the learning experience. So I started with new fuel lines, primer bulb, new prop, rebuilt the lower unit with new seals and water pump, adjusted the shift cables so reverse and forward works, rebuilt the fuel pump, the carbs and float bowls, now the starter. But I am having fun! Redid the electrical on the boat, now all lights work, and I installed a new tach! Certainly has been an interesting summer. Nice thing is it has not been too expensive, since I am doing my own labor!
                      Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

                      Comment


                      • #12
                        You know, after all the work on this thunderbolt 800, think I would enjoy rebuilding another engine. It has been quite the learning experience. So I started with new fuel lines, primer bulb, new prop, rebuilt the lower unit with new seals and water pump, adjusted the shift cables so reverse and forward works, rebuilt the fuel pump, the carbs and float bowls, now the starter. But I am having fun! Redid the electrical on the boat, now all lights work, and I installed a new tach! Certainly has been an interesting summer. Nice thing is it has not been too expensive, since I am doing my own labor!
                        Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

                        Comment


                        • #13
                          One last follow up, the new starter motor came in on Saturday. It was exactly like the original, except it was 1/2 inch longer! The top of the starter was the same, so it meshed with the original top mounting plate perfectly. The bottom holding bracket was 1/2 lower, so the bolts in the mount did not line up with the screw holes in the head. I had to drill new holes through the aluminum in the lower mounting bracket before I could get the bolts back into the head (between the carbs). But it is on, all together, and it turns the engine over! []
                          Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

                          Comment


                          • #14
                            One last follow up, the new starter motor came in on Saturday. It was exactly like the original, except it was 1/2 inch longer! The top of the starter was the same, so it meshed with the original top mounting plate perfectly. The bottom holding bracket was 1/2 lower, so the bolts in the mount did not line up with the screw holes in the head. I had to drill new holes through the aluminum in the lower mounting bracket before I could get the bolts back into the head (between the carbs). But it is on, all together, and it turns the engine over! []
                            Mark Kriz[br]Mako15 1974[br]Mercury Thunderbolt 800 1972[br]Maple Valley, WA[br][br]

                            Comment

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