Air nailers and staplers have been in use for the better part of a century and have changed very little in that time. A wellbuilt nailer, or nail gun, as they are sometimes called, can last for decades with proper maintenance. Provided the case of the tool remains intact and is not severely bent, most issues can be solved by cleaning the nailer and replacing the plunger cylinder and O rings. Most manufacturers sell rebuild kits which contain the parts needed to make this repair. The basic repair procedure is the same for almost all air nailers and staplers.
Size an Allen wrench to the four mounting bolts holding the square grill to the back of your nailer. This is located at the top and rear of the tool at the opposite end of the barrel, and typically has a louvered, or ported, vent cover to allow air to escape. Turn the bolts counterclockwise to loosen and remove them.
Use a utility knife blade to pry the square vented cover from the tool and remove it to expose the plunger cylinder chamber. Grasp the white or black plastic disk at the centre of this chamber and pull it from the rear of the tool. This is the plunger cylinder and will have a flat metal rod at its front end, encased in a moulded plastic fitting, with black rubber bands around it. These bands are the O rings that provide a seal for the air, allowing the pressure to release, driving the plunger forward to drive fasteners.
Spray an aerosol cleaning agent, such as a tool or parts cleaner, up into the chamber of the nailer. Tip it with the open rear facing down to allow the cleaning agent to run out, taking oil and grime with it. Run a cotton swab around the interior of the chamber. Repeat the application of the cleaner if the cotton swab comes back black. Allow the cleaner to evaporate for fifteen minutes.
Inspect the cylinder and metal plunger. If it appears to be undamaged and the metal plunger is relatively free from deep scratches and is straight with smooth edges, remove and replace just the O rings. Stretch these elastic rubber seals to remove them from the cylinder. Position the new O rings in the same grooves on the cylinder.
Replace the entire cylinder and plunger assembly if you see signs of wear, such as cracks in the plastic, or a bent or grooved plunger. Apply air tool oil to the O rings with a cotton swab to keep them pliable and aid in the airtight seal, as well as providing lubrication for the plunger. Press the cylinder back into place, aligning any grooves or notches with the opening of the tool case, to ensure proper positioning.
Clean the inside of the vent cover with a clean cotton swab and acetone to clear dust and debris from the grill. Replace the vent cover on the rear of the tool the thread the mounting screws through it. Tighten them with the Allen key.
Apply three drops of air tool oil into the inlet fitting, or air nozzle, on the bottom of the nailer, directly below the vent cover. Reattach the air hose, and fill the magazine with fasteners. It is now ready to use.