No announcement yet.

Unsticking stuck pistons

  • Filter
  • Time
  • Show
Clear All
new posts

  • Unsticking stuck pistons

    Howdy all,

    I left a very rare engine outside under a tarp a bit too long and now I have rust in the bores. Any suggestions on the best chemical to try to get them to a state where I can slide the pistons out?

    Thanks, Derek (who needs more storage for more engines...)

  • #2
    Hot Diesel down the bores is a good start and keep rocking the crank. If the pistons are really stuck badly, then filling the cylinder with grease and hooking up a grease gun will often get the job done. The pressure will both push the piston AND expand the bore to get things moving.
    Paul Compton


    • #3
      I bought an old 39 Plymouth 6cyl and the number 4 cylinder was packed with rust. Disconnected the rod and swung it out of the way and after spending several hours on cleaning the cyl - the piston was all the way down - and letting it soak with tranny fluid for 2-3 days, my buddy and I rigged up a small hyd jack positioned over a block of wood roughly shaped to the size of the bore pushing against a chain bolted to the head bolt holes. pumping the jack pushed the piston down with the block and pretty easily moved it about 1/2-3/4" which was enough to start 'wiggling' the piston and get it out. Dang thing cleaned up amazingly and we started it up and ran like a top!
      If everything seems to be going well, you have obviously overlooked something........


      • #4
        You don't say what type of engine this is, Big or in a truck or?
        Anyway, as stated a penetrant, and if this is a stationary engine , a heat lamp to help warm the block and penetrant will greatly help, works good.


        • #5
          Use a 50 / 50 mixture of ATF and acetone. Shake and keep mixed.
          Been used for years with great results.
          Works on rusty bolts etc.
          Hope this helps.
          olf20 / Bob


          • #6
            What sort of engine? Complete, head off? Air cooled, liquid cooled, cast iron, sleeve aluminum block? How many cylinders? 2 cycle 4 cycle? How much rust is built up? A flash over, flaky rust, packed full?

            I would start tearing the motor down, get head, pan, and all off I can. Figure out what kind of rust we are dealing with and we can go from there. Light rust may just need an oiling and working to get loose. Built up rust might take some scraping and work to get the piston moving.


            • #7
              I've used brake fluid with sucess.
              "Let me recommend the best medicine in the
              world: a long journey, at a mild season, through a pleasant
              country, in easy stages."
              ~ James Madison


              • #8
                Originally posted by olf20 View Post
                Use a 50 / 50 mixture of ATF and acetone. Shake and keep mixed.
                Been used for years with great results.
                Works on rusty bolts etc.
                Hope this helps.
                olf20 / Bob
                Now's the time to give it a try, that's what I would shoot for, that or that Kroil everyones been talking about...

                Keep in mind this very important thing, the amount of leverage you will have on the piston by rotating the crank is in direct relationship to where the piston came to rest, if half way down the bore you will have the least effect and can really pour the coals to your breaker bar - if close to TDC or BDC you will have greater effect, if really close to TDC or BDC you need to be aware that you could easily bend a connecting rod if your not careful,
                Different engine configurations require different judgement,

                in line 4rs or horizontally opposed 4rs are easy to figure out as all pistons will be parked at the same leverage advantage with 2 @ TDC and 2 @ BDC or all halg way down the bore,
                but V/6s and V/8s play by a different set of rules and while some pistons will be at great leverage advantage others will not...

                if the heads are off then by all means use a nice block of wood and tap to try and get things moving. this will trump anything you can do with the crank and rods...
                but whatever you do - do not use excessive force or you can either bend or break parts or tear metal from the bore...

                go within reason and 100 little taps are way better than 10 huge ones - If you have an mild air hammer with a hammer head bit use it with a block of wood inbetween it and the piston and it will help distribute that penetrating oil to the frozen places...


                • #9
                  If its a small engine, you can solder a grease fitting to a spark plug with the porcelain removed. Soak the piston top with what ever penetrant you want. Then pump the cylinder full of grease. It will hydraulically break it free without any damage to the rings. I did this for years on junk boat motors to free them up.


                  sorry, upon closer reading, this was already suggested


                  • #10
                    i've been told coke-a-cola is good at breaking down corrosion, left for several days, might be worth a try if you have time on your side



                    • #11
                      I've used burnt motor oil to free up old tractor engines for years.Burnt oil from a diesel works best,seems to be more acidic???Anyway,it's easy,just fill the cylinders up and let time and gravity take effect.Usually takes about a week of soaking to free up dry,rusted bores.
                      I just need one more tool,just one!


                      • #12
                        On the old iron forum the preferred treatment for parts seized by rust is... WATER.
                        Believe it or not....
                        Good luck!


                        • #13
                          I think my dad used kerosene/oil. Might have used some "Liquid Wrench" also. Had a F-20 Farmall that had seized, we used that mix and a piece of timber on top of the piston and a heavy hammer to convince the piston to move. We weren't trying to save the pistons, just wanting to loosen for disassembly.

                          Mentally confused and prone to wandering!


                          • #14
                            re: Jon Herons post about using water, i saw that also, and apparently it does work.

                            Think i'd rather have an oily substance, but the water would seep i think.


                            • #15
                              There seems to be a lot of belief in used motor oil from a diesel to unstick seized engines. I tried it once, on a sized from sitting indoors Honda 4 cylinder m/c engine. Filled all cylinders and let it sit for a week or so. Engine turned over freely after that.
                              They were not heavily rusted.