Making an air compressor from an old 2 stroke

Discussion in 'General Questions' started by zippinaround, Sep 21, 2016.

  1. zippinaround

    zippinaround Active Member

    Just wondering if anyone has ever made their own compressor from an old 2 stroke? I was thinking just blank the exhaust port and put a one way valve in the plughole , not sure about keeping it lubed?

    My plan was to make it pedal powered so I get some exercise , fill a tank with air and also save money , possible ? Or just another crackpot idea?

  2. Frankenstein

    Frankenstein Well-Known Member

    As far as the exhaust pipe idea goes? If this is strictly pedal powered it would work, it will also get pretty close to impossible to make work, reason is the exhaust is helped by the piston pushing the new gas in via transfers. The second part is the engine keeps the cycle going because of the counterweights. At a stand alone feature the piston will pump air out the exhaust and the intake at the same time, then not at all as it gets up past the transfers and exhaust, at that point you have to overcome more than 100 psi, but that doesn't do anything because it decompresses to atmospheric pressure by the time it reaches the ports on the down stroke.

    In theory if you pedal fast enough you can be seriously injured by some sort of lung failure, at that point the hospital should provide some kind of air pump that would be more efficient.
  3. butre

    butre Well-Known Member

    you should be able to get away with sealing the exhaust port and putting a check valve in the plug hole. once the tank starts getting some volume in it the pressure in the tank will start holding the ball down and it'll begin blowing off at higher and higher pressure until the tank gets to whatever the cranking psi in the cylinder is, at which point it'll just be like the motor is turning over without firing. as for lube, just let it drip into the intake and put an oil separator on the fittings leaving the tank.

    I've attached a picture of one of my older compressors, that sock is being used as an air filter, it's just an open intake with an oil drip system attached to it. I don't bother separating out the oil because I don't paint with it.

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  4. zippinaround

    zippinaround Active Member

    Excellent , thanks butre I once seen one at a "casting factory" aka the guys back yard , he had everything set up to work without any power , drills ,grinders, his forge , spray painter everything ,when I was there he was making a load of cast iron railings was a great eye opener
  5. butre

    butre Well-Known Member

    even better than the oil drip system: seal the intake and transfers, lower the case compression ratio and put an inch or so of oil in the case and just use the exhaust port for intake, but then you may need to add to the static compression to bring the cranking PSI up to acceptable levels. a stock straight plug motor would only get around 70 or 80 PSI without help from the crankcase. a 5cc head would bring you to the 140-150 range.

    some crankcase ventilation would prevent the need for lowering the case compression ratio
  6. You make it sound so easy lol
  7. butre

    butre Well-Known Member

    it is easy, drill a hole in the top and bottom of the case, tap the top for a pipe fitting and put a breather filter on it, tap the bottom for a drain plug, make a block off plate for the intake and fill the transfers with jb weld
  8. zippinaround

    zippinaround Active Member

    Need to pay a visit to the scrapyard see what I can dig up , really just need a tank I'm thinking something small like a small trucks brake tank , fit a v belt cog to the engine crank and the other end in a rim with no tyre , bike on a stand .
    It does seem like an easy concept whether it will work effectively is another story haha