Generally, when you attempt to fire and only get an air sound at the trigger, the problem is air leaking past the orings in the head valve. Here are a few things to check and a simple test.
Remove the trigger from the gun so that you can have access to the trigger pin. Remove the nails from the gun. After removing the trigger and the nails, reconnect the air supply (check for 100psi) Place the nose of the gun against wood and with a very quick ****, depress the trigger pin all the way in. If the gun fires then the safety foot is not allowing the trigger to depress the pin all the way in. Make adjustments to safety and check for worn trigger and trigger retainer pin. If the gun does not fire, remove the head. Place the head on table and depress the headvalve all the way in with your thumbs then place a finger over the small vent-hole on the gasket surface and release thumb pressure. The headvalve should remain depressed due to vacuum in the valve and will pop up when you remove your finger on vent hole. If the headvalve does not stay in, air is leaking past the orings. Remove headvalve parts and use magnify lens to find small scratches on the surface where orings contact. Remove scratches with very fine sandpaper (300 - 400 grit) Make sure all the orings are not cut (use magnify lens) and fit snuggly. Lube with "Danco silicone grease" available at lowes in the plumbing department. It is used to lubricate orings in faucets. After re-assembly, do vacuum test as described above. If you have vacuum, head is ok. Make sure that the gasket seals around the vent hole where the head mates against the body. You should be good to go. Good Luck and email if you have other questions.
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I probably didn't get enough grease on all of the orings on the one that I rebuilt. The packet that came with the kit wasn't enough. If I take it apart again, what kind of grease should I use. Also,I am wondering if that recoil spring is worn out.
After writing the first comment, I took apart the other gun and put it back together and it fires again.
What part is the bumper? I have an exploded diagram to reference
Just use a light lithium type grease and the bumper goes under the cylinder between the cylinder and the nose. make sure it is not deteriorated. the othe solution given is also valid for checking the head valve for suction. After putting back together make sure that you put in about 6 drops of air tool oil also.
without knowing what you did, I would suspect that an oring might be pinched or stuck, did you grease the new orings slightly when installing. Also take a look at the seal on top of the cylinger and the exhause band on the lower part make sure the holes are clean. What is the condition of the bumpers. Usually after I rebuild them I have no problem so I would carefully disassemble the one that was rebuilt and look everything over for the above.
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