How to repair hitachi nv75 coil gun - Hitachi NV75AG Coil Siding - Framing Nailer

could be in need of an internal adjustment to stop the hammer from hitting the end plate ( travelling to far)
talk with a tool repair shop and see if there is something that can be done
contact a a hitachi service agent for advice
go google and type in--- repair manual for Hitachi nail gun-- and see if there is a manual in pdf version that you can download

Remove the 3mm roll pin holding the trigger in place and set aside the trigger plunger (white plastic plunger should have an oring on groove). Remove the fitting that holds the trigger plunger and replace vinyl ball #875645 or check for debris under ball. Good luck with your repair.

I have seen roofers that can make the gun sound like machine gun. What they do is fine tune the adjustment on the safety foot up or down and slide the gun against the roofing material while bouncing the gun slightly instead of lifting the gun off the work while pulling the trigger. The safety foot should be pushed against work while sliding the gun from one side to the shingle to the other. The firing takes place when the gun is push down slightly, so that means that the adjustment has to be so the gun does not fire until you press down the final 1/16 to an inch or so. This action wears out the nose however due to rubbing against the shingle. One must balance the faster wear of the nose against greater productivity.

Your description makes it clear that it needs a head rebuild kit. You can order this from Hitachi, or send it in to local Hitachi center. Good machine, straightforward repair. If you are a little handy, you can do this repair yourself. remember to oil the gun frequently to make your repair last longest. Farmerbear at FixYa

There are o-rings in the gun that route air around the cylinder to push the driver back up. One or more of these o-rings are worn or broken. You can get it fixed at a service center or you can go to sites like www.ereplacementparts.com to find a breakdown of your gun and order the parts. Unfortunately Hitachi doesn't make all in one repair kits and if you replace one, replace all of the o-rings.

You did not described if there is piston movement when you squeeze the trigger or push outlet into the material. If there is piston movement but it is too weak to push the nail, insufficient air supply is first obvious reason.

Eliminate insufficient air pressure or volume supplied to the piece. Air pressure supplied should be between 70psi to 120psi (4.9bar to 8.3bar), air hose should be at least 7mm internal diameter.

If air supply was eliminated, disconnect air supply and check if piston is not locket in one position, you described that you done some maintenance on the machine. I assume therefore that you will know how to check piston for movement, if there is some restrain, you need to find what is causing it and remove obstruction.

As you put gun together, do not forget to lightly oil all assembly surfaces with compressor oil.

This is very good gun and should serve you for many years to come, we use these for last about 8 years rather haevily without any problem (except aprentices...), hope you will have as good service from yours.

Please send note what was the reason, and how did you solved it.

Hitachi nv45 series is the most popular line of nailers amoung professional roofers. There are three areas that develop leakes. Leak out head vent indicates cylinder stuck in lower position or headvalve worn. With air connected, gently rap head of gun against rubber mat to move cylinder to position. (Use caution not to damage head). If this action works, gun needs cleaning internally or lack of oil. If air still leaks out vent remove head and examine valve in head and replace as needed. Check that cylinder moves freely up/down (travel aprox 1/4"). If cylinder is hard to move pull cylinder and clean replacing orings as needed. If leaking around trigger, remove rollpin and trigger and check nylon ball for pits and replace as needed. If leaking around base of gun check for loose bolts and/or worn gaskets. Remove nail canaster to check feed piston gasket and screws. Good luck with your repair and post again if you have other question.

There are some adjustment But for safety reason's it could also be dried or sticky safety switch ,you could try setting or oiling it, But should probably let the certified repair shop do the job, that may alleviate you of some liability . hope this helps .

the top!! o-ring inside of thr top plate is bad you need to remove the plate /dissasemble and replace the o-ring

yes my guns i rebuild once a year at least