Question about Hitachi NV45AB2S Coil Roofing Nailer

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I have been rebuilding Hitachi nalers for about 2 years now and this one has me stumped. It works fine if you single shoot it. If you hold the trigger and try to bounce shoot the nails, the driver will not return fast enough.

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The roofers that frequent my shop want their nailers to work like machine guns. Here is what I do to make the hitachi 45 nail fast. Remove the cylinder and sand the fine scratches where orings meet cylinder. I use a rubber slug with a small bolt through the center. The rubber slug fits snuggly into the cylinder and the bolt into chuck of drill. Turn the cylinder with the drill while holding fine sandpaper against the scratches untill smooth. remove the nose from body and replace the sheet (part # 877125) and the bumper. If the sheet fits loose on the driver and the bumper has cuts or missing pieces, the driver will not return with full force. also the oring on the piston should not be too tight. Just snug enough to hold the weight of the piston. While nose piece is off check the air passage to feed piston for trash, use a small wire and push through to make sure. Make sure the orings on the feed piston fit snug. Actually push the feed piston by hand in the nose piece to make sure the three orings fit snugly. A loose feed piston will reduce nailing speed. Finally replace the boot on the firing pin. If the boot is blown off its seat with use replace the firing pin. A loose firing pin will waste air and lower pressure reducing nailing speed. Good luck

Posted on Dec 02, 2008

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My hitachi roofing nailer isnt working properly no leaks but whenever I shoot the nail it just spits out as if it had no pressure to it.


You might have bad seals on the piston, if the seals leak you lose power but it won't leak externally. Hitachi guns are nice but like oil, daily oiling or twice daily under heavy use will keep the seals fresh for years.

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1 Answer

Driver not return


How old is the nailer. If it is old enough and not oiled each use, O rings get damaged and will leak air at piston and trigger valve. Depending on the brand a rebuild kit may be available with new O rings and trigger valve.

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i think you have two different problems , replace the feeder spring, and replace the oring on the driver piston. also make sure that the coil of nails is perfectly round if they are dropped or squeezed tool will not work right

Sep 11, 2012 | Hitachi NV45AB2S Coil Roofing Nailer

1 Answer

No nail or double nails


Usually due to bent driver, worn driver oring or lower bumper cracked, weak or broken feeder spring. Remove head being careful not to tear gasket. Pull the driver and check for bend in shaft or chipped end. If the end of the driver is chipped or rounded, grind tip flat (remove as little as possible ). Piston should hold position in the cylinder and drop down under its own weight. Examine lower bumper. If missing pieces, replace with new. Lube orings with silicone paste (sold at Lowes in plumbing department). Also check for correct nails. Should be 15 degree metal wire. There is an older hitachi nailer with a metal canister (nv50aa) that uses plastic strip nails. These nails are too close together to work properly in the #nv65 gun and will usually shoot two nails. Good luck

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Most nailers work better by bump firing the gun. Less likely to double fire. This is a common problem amoung brands. If you place nailer on work then trigger, you may/will have problems as you describe. There is usually an option of triggers or builtin method of single firing the gun. With single fire trigger, you can place gun on work and fire. The will not reset for next round untill you let go of trigger and lift gun off the work. If your gun is double firing even with bump method, then replace the trigger valve.

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One or more of the rubber o-rings inside the gun are worn or broken. Air is leaking out of where it needs to go to push the driver back up. This is a good gun and worth rebuilding. Unfortunately Hitachi doesn't make rebuild kits for their guns, you have to have a breakdown and order each part you need seperately. If you do this, replace all of the o-rings, if one went bad the others are not far behind. If you take it to a repair shop make sure they repalce all the o-rings.

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1 Answer

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I have had this problem myself, the only fix is a rebuild kit which you can pick up pretty cheap on ebay. the kit will consist of a bunch of seals and just pay attention to the way you take it apart and you will have no problems

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1 Answer

NV45AB2 worked great a year ago.hooked it up last week and it only shoots the nail 1/4 inch in a piece of wood and it wont advance the next nail.My framing nailer works so the hose presure is good.


if you havent used in a year the o rings could be dry and you can try and lubricate them, but sounds like it needs them replaced. You can try going to Nailgundepot.com and buying an o ring rebuild kit from them. It contains all the needed parts except for the grease to lube the o rings. Let me know if you need more help

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1 Answer

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I had the same problem with my Stanley stape gun. Had to replace all the seals and piston. Works find now! Check-out internet ...search for a rebuild kit for your model of gun. Get the complete rebuilding kit ....take about 1/2 hour to rebuild.

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