How to Rebuild an Air Compressor Pump

This video from Sears PartsDirect shows how to rebuild the pump in an air compressor. The compressor motor drives a piston that compresses air in the tank. Worn pump parts and seals prevent the pump from filling the tank with compressed air. If the pump won’t compress air and fill the tank, you may need to rebuild the pump.

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The video includes these parts and tools. Look up your model to make sure you get the right parts for your air compressor.
Connecting rod kit

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The compressor motor drives a piston that compresses air in the tank. Worn pump parts and seals prevent the pump from filling the tank with compressed air. If the pump won’t compress air and fill the tank, rebuild the pump using the steps in this video. Before you begin, wear work gloves to protect your hands. Unplug the air compressor’s power cord from the wall outlet. Pull the ring on the safety valve to bleed all air pressure from the tank. Remove the front shroud mounting screws. Using a slot tip screwdriver, pry the shroud halves apart at the locking tabs and remove the front of the shroud. Remove the back shroud mounting screw. Remove the back shroud. Remove the air outlet tube from the pump head. Remove the mounting bolts from the pump head and lift the head off the pump. Lift the valve plate off the pump. Remove the fan mounting bolt and pull the fan off. Loosen the Torx screw that clamps the piston connecting rod to the eccentric bearing. Pull the connecting rod off the eccentric bearing. Push the piston and cylinder sleeve up and out of the pump body. Push the piston out of the cylinder sleeve. Remove the Torx screw from the top of piston. Remove the piston cap and compression ring. Place the new compression ring on the top of the piston. Reinstall the piston cap and Torx screw. Slide the new cylinder sleeve into the pump body. Insert the piston into the new cylinder sleeve. Push the piston connecting rod onto the eccentric bearing. Align the piston connecting rod flush with the eccentric bearing. Tighten the piston connecting rod Torx screw to 48 inch-pounds using a torque wrench. Push the fan onto the keyed shaft. Reinstall the fan mounting bolt. Tighten the fan mounting bolt to 120 inch-pounds. Press the new valve plate seals into the seal channels on the new valve plate. Place the new valve plate on the pump body with the reed valves positioned on the handle side of the air compressor. Position the pump head over the new valve plate with the muffler side of the pump head over the reed valves on the valve plate. Reinstall the pump head mounting bolts. Tighten the pump head mounting bolts to 7 foot-pounds. Reinstall the outlet tube on the pump head. Position the large half of the shroud over the compressor and install the back screw. Slide the smaller half of the shroud into the large half of the shroud and engage the shroud locking tabs. Reinstall the front mounting screws in the shroud. Plug the air compressor into the electrical outlet.



7 thoughts on “How to Rebuild an Air Compressor Pump

  1. Is their a way to tell if the compressor is bad? Or if it's my pressure switch? I have a 1995 craftsman model 919 and it just kicks on a few secs(fan turning) then shuts itself off. Notsure if its pressure switch or maybe compressor went bad. Runs 3secs or so an "click" an shuts off. Plz reply of can

  2. you show the new compression ring as being pre formed to fit. The parts I received were flat and if bent upwards to fit into pump body, the ring extends beyond the piston cap, whereas the new part shown does not even quite reach the top of the piston cap. Do I trim it to fit and should the ring extend past the cap?

  3. What if the pump shaft will not spin? Locked up? Seized piston I assume, and it's a dual valve assembly. How much damage did that cause and do you think it's worth rebuilding? The pump assembly is over $400! I could buy a new one for about the same.

  4. I followed your instructions and they were great EXCEPT for the foot pounds torque that you mentioned for the cylinder arm to the bearing. The 48 lbs that you recommended blew out my thread on the old aluminum. Whoever is watching this video, I do not recommend this torque for this part of the instructions. I now have to either spend a crazy amount on a kit (70+$), tap a new thread into the arm and use a larger screw OR.. throw the compressor away. All this happened after I purchased a bunch of parts from to repair what this video mentions. I don't think even in a NEW state, that screw needs 48lbs of torque.

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