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What's the best material and fit for an oil-less air compressor piston seal?

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  • What's the best material and fit for an oil-less air compressor piston seal?

    I've got a Task Force air compressor which wasn't making pressure. The cylinder was scored and the seal on the piston was folded down and split on one side.

    I've turned and polished the cylinder bore. Now I need to make a new seal for the piston, but I'm not sure what to make it from. The piston is about 2" in diameter. It doesn't have a piston pin, so it rocks as it goes up and down in the bore. The seal is clamped to the top of the piston with an aluminum disc. This is the old seal:

    It appears to be some sort of plastic, but there are no markings on it.

    I've got some UHMWPE and some Delrin. Would either of those work for the seal?

    Also, what kind of fit should I have between the piston and the bore?

    I've tried to find a source for parts, but Lowes no longer carries TF compressors. The place they recommended for parts only carries parts for items still sold in the store.
    Last edited by winchman; 11-30-2010, 05:34 PM.
    Any products mentioned in my posts have been endorsed by their manufacturer.

  • #2
    UHMW is used in some pneumatic and hydraulic seals as it has fair resistance to oil. But have you checked with seal manufacturers/hydraulic supply shops for the seal? Forget what it came from, you just need the specs on the seal. Looks like a typical design, and seals aren't that expensive, what with cylinders and pumps being rebuilt all the time. Just google "hydraulic seals" and you'll find a ton of sites with info to peruse.


    • #3
      Any Delrin (acetal) that I am familiar with would be much too rigid for this application.

      The seal needs to have a thin flexible edge to seal in the bore as the piston rocks to follow the crank pin.

      UHMW might work if the cycle was limited to one tank fill up, but I don't think it would tolerate the heat for any kind of continuous use.

      I think some kind of teflon would be the best.



      • #4
        Repair kits for that type of compressor are very cheap.


        • #5
          Where do you get them? I've searched online for about an hour. The closest thing I could find was a link to the Sears parts site that says the item is not economical to repair:

          Maybe that's why it was in the dumpster.
          Last edited by winchman; 12-01-2010, 02:15 AM.
          Any products mentioned in my posts have been endorsed by their manufacturer.


          • #6
            After listening to my neighbors similar compressor from over 600 ft away, without my hearing aids in..

            The cheapest repair is to chuck it right back where it came from. Hearing aids cost BIG money...

            Worthless 40 hour life, NASTY LOUD machines...

            Beancounters over brains.. Buyers the same...

            My dad was a commercial painter for 30+ years. Told me long before those cheap ones came out, to get a cast iron pump (pref with pressure oiling) with seperate belt driven motor.
            Last edited by Bguns; 12-01-2010, 06:28 AM.


            • #7
              Bguns is 100% correct
              Toss that cylinder out, Buy a nice oil lubracated *LOW RPM* piston compressor. $200~ or so, And change the oil once a year, insted of the seals once a month!

              My low rpm 2hp piston compressor is quite enough to talk over, What a consept!
              My higher RPM 5hp compressor.. Maybe you can shout over it. But then, its a much bigger unit.

              Every 1hp oilless compressor iv heard is even louder then my 5hp compressor.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


              • #8
                on the other hand, they dont mind falling over......being sat at an angle or even being pushed over while running....... all real risks out of the shop....


                • #9
                  mcmaster carr has cup seals. If it is very old it may be leather.
                  Herm Williams


                  • #10
                    Sears sold kits in the past. If you look up Porter Cable, or others, you will find kits for them. Sears seems to have copped out. I am not sure who makes the Sears compressors, but maybe they still sell them.


                    • #11
                      I always wondered (if a guy wanted to) could a 4cycle gas engine be used as a compressor? Say something with an oil system and two cylinders like a lawn mower motor.


                      • #12
                        There was a company that made kits to convert VW engines into a compressor. They were based in North or South Carolina. Also years ago when spark plugs were more accessible they sold a spark plug replacement to put into a cylinder and use for emergency air for tires. Did see it used once sometime during the 1960's. He aired up a flat tire.


                        • #13
                          I built this compressor in 1967 from a junked lawnmower which had a bent shaft. The motor came off a junked washing machine. The pulley is off a '55 Chevy. Everything else on it eas either free or from the junk pile, except teh new hose I installed about ten years ago. I put the original oil back in it after I cut off the shaft and it's still there.

                          I made the new seal out of UHMW-PE this morning, and the old Task Force compressor has rejoined the living, at least for a while.
                          Any products mentioned in my posts have been endorsed by their manufacturer.


                          • #14
                            I also understand winchman and his desire to repair the compressor. More fun fixing junk. If there is time and parts cost are low go for it. However the opinion is, the oil free compressors are the worst sounding pieces of junk ever built. For that reason alone it may be best to put it into the scrap or turn it into other uses.


                            • #15
                              Good for you winchman!

                              I, for one, would be really curious how well the UHMW holds up, could you let us know? Did you take any photos of the part you made?

                              Thanks, Dave