Why does my Hitachi nv45ab gun double fire nails?

If the trigger is worn out it can cause the nail gun to double fire. If the gun is set to bump fire and it is double firing in this setting then replace the trigger valve. If the nailer is set to trigger fire, then leaky O rings on the trigger valve can cause this.

Full head or not?

The allen screw/s that you mention are there to plug holes where automatic equipment would normally connect (such as automatic nailing machines) . This is only a plug and should not be driven in too far. I have also seen allen screws installed in the head to repair small crack/s.

This is a bottom fire tool. (NV83A2) You need to hold the trigger down and then as you place the nailer to the wood the safety will depress and it will fire once. This is usually done in one, swift action. If you do this in the opposite way by placing the tool to the wood and then pulling the trigger they often will double fire.

Best practice is to bump fire the gun to prevent double fire. Do not place the gun on the work and pull the trigger. This takes practice while using at an angle. Works better if the nose piece has rather sharp points to help nose to stay in postion while you bump. With trigger depressed, practice without nails bumping/hitting wood at different angles untill you can bump hit at the spot that you need the fastener. If the gun double fires while bump-firing, most likely all the safety/trip parts are worn/loose. Not expensive to replace. Good luck.

New user will jam the gun/ nails because gun was most likely not bump fired. Placing the gun then depressing trigger will usually cause double fire in the hands of new user. New user should practice on scrap lumber bump firing at many angles till they get the idea; or give them a training period with a nailer that has a single shot trigger (they may develop bad habits with single shot however).

The condition of the driver oring is an indication of wear of all the other orings in the gun. Remove the nails and lightly tap the nose against piece of wood. If the driver drops to bottom of cylinder the oring is worn out and time for oring kit. Hitachi nailers are sensitive and will double fire if placing the foot against work then depressing trigger. Adjust the depth thumb screw several turns either direction then depress trigger and quickly bump gun against work. Good luck with your repair.

Most all nail guns can be converted to single fire, however, usually parts must be changed. Some brands have two positions on the trigger, others have a button position near the trigger to accomplish same. Check with dealer or email your gun model # and I will explain your to fix. For now you can replace the spring on the safety with one slightly stiffer. Also try nailing with trigger depressed and quickly bump the gun to fire, this method usually works better than placing the gun in position then firing. Good luck with your repair.

Nail guns either have a switch or a seperate trigger assembly for two options - automatic, or 'bump' fire, and sequential fire. Sequential firing may be best for you since the nose must be fully depressed and the trigger pulled for each nail.

If you're stuck with bump firing, practice your technique. Double fires often occur when the workpiece bounces back into the nose of the gun; learn to 'bounce' the gun off the material to avoid this second contact.

If you're getting double fires in sequential mode, the problem could be more serious. I keep a can of aerosol silicone lubricant on hand to clean and lubricate the feed mechanism and magazine. Make sure your tool is clean and lubricated before each use, including the 3-5 drops on the air coupling.

Check that your air pressure is not set too high. Overdriving nails reduces their effectiveness and can cause tool malfunction.

This problem could also be caused by worn out O-rings or other parts within the tool. If you're not comfortable servicing the tool yourself, take it in for repair/maintenance work.

Another important thing to remember: With tools like this, you get what you pay for. A cheap nailgun will never function as well as a quality nailgun.

There is one main part that can be the cause of the problem.

The trigger. Check to see if there is anything out of the ordinary with this. There should be some moving components attached to the trigger itself. Is any part of the trigger touching the button in the body of the gun when safety is not depressed. If the lever on the trigger is pushing on the button, even a little bit, It will allow the gun to fire again and again.