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How to free up seized engine?

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  • How to free up seized engine?

    One of my landscaping customers recently gave me a 1970 Merc 7.5. Was stored in his shed for at least 10 years. Motor looks good, no signs of a lot of use. But! can't turn over the engine. I squirted "PB Blaster" penetrant into the cylinders, and tapped the pistons lightly daily. But, after sitting for 10 days or so, won't budge. A friend suggested that the driveshaft gears may be frozen. Before I take the lower unit off (never did it before) is there anything else I should be trying? Is there any way to determine the source of the seizing with out dismantling engine components? Thanks for any suggestions.


  • #2
    Re: How to free up seized engine?

    The best way to tell if the problem is in the top or the bottom is to seperate them. I had a guy bring his motor in and it was frozen tight.He said he filled the cylinders with oil and let it sit for a week or two and it was still frozen. I dropped the lower unit and found a bushing on the driveshaft that bound the motor up.

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    • #3
      Re: How to free up seized engine?

      PB Blaster is o-k but for stuck pistons I like :3 parts Marvel Mystery Oil1 part Liquid WrenchKiller stuffc/6Hooty

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      • #4
        Re: How to free up seized engine?

        My friend had the same problem. He made a gizmo from a sparkplug. It had a zerk fitting in it. He pumped grease in and "voila" no more stuck piston.

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        • #5
          Re: How to free up seized engine?

          Hmmm...how did your friend get all that goo/grease back out of the cylinder after it broke loose?

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          • #6
            Re: How to free up seized engine?

            DON'T MESS WITH THE CYLINDERS UNTIL YOU REMOVE THE LOWER UNIT AND THEN TRY TO TURN EACH INDIVIDUALLY. COULD BE IN THE LOWER UNIT.SORRY FOR SHOUTING, TOO LAZY TO RE-TYPE

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            • #7
              Re: How to free up seized engine?

              If you drop the lower unit and the powerhead is still stuck, by all means tear it down. Those Mercs are all steel bearings in the powerhead, and in all likelyhood there's going to be surface rust on some of them. A good check to see how extensive the "frozen-ness" of the powerhead is - is there ANY play at all in the flywheel? If you can move the flywheel (and by extension the crankshaft) then you might only have a stuck piston and not rusted bearings. In any case, I would tear it down to be sure, as even if you free it up and then run it with rusty bearings, it won't run for long. And then you'll have a toasted motor... Also, if the cylinder walls are rusted up or if the rings are stuck, the motor may run, but it won't run well.Eliminate the lower unit as a cause first, then go after the powerhead. A good manual will help (Selocs aren't bad for an aftermarket manual). They're good running little motors and worth putting a little time and effort into it...- Scott
              Share A Project Page for 1971 GW Invader Banchie 13
              http://www.shareaproject.com/pages/p...,p,433,00.html
              Share A Project Page for 1976 American 18
              http://www.shareaproject.com/pages/p...,p,404,00.html
              Share A Project Page for 1974 American 15
              http://www.shareaproject.com/pages/p...,p,405,00.html

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              • #8
                Re: How to free up seized engine?

                SCOTT GREAT REPLY. V

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                • #9
                  Re: How to free up seized engine?

                  Thanks to all for useful info. BTW, Scott, I can jiggle the flywheel back and forth only an eighth of an inch or so. Does that tell me anything?Anyhow, looks like it will be next month before I can dig into it. Will report back with, hopefull, my success story.Wayne (N. Kingstown, RI)

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                  • #10
                    Re: How to free up seized engine?

                    Hi Wayne, The crankshaft moving is a good sign. It doesn't eliminate possible bearing problems in the crankshaft assembly, but it sure points to piston issues instead. When you get it apart, I would press the pistons out. It generally does the least damage and is the least messy of all the methods of stuck piston removal. Most shops have a bench press for bearing insertion/removal and it'd be easy to use a dowl inserted in the plug hole to press the piston out. Check the bearing races on the crankshaft/rod journals as well as the mating races on the connecting rods. A couple of small pits aren't a huge issue, but a series of vertical line pits could pose problems. You should be able to get new piston rings through a dealer. Upper and lower bearings & seals are available throught a dealer, as well as bearing stores...- Scott
                    Share A Project Page for 1971 GW Invader Banchie 13
                    http://www.shareaproject.com/pages/p...,p,433,00.html
                    Share A Project Page for 1976 American 18
                    http://www.shareaproject.com/pages/p...,p,404,00.html
                    Share A Project Page for 1974 American 15
                    http://www.shareaproject.com/pages/p...,p,405,00.html

                    Comment


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