Dismantled gun to fit new circuite assem. small spring and z shapedflat steel piece fell out from the nail exit jim

I presume the gun fires but no nail is ejected. A possibility is jammed nails in the magazine. Do you see a mark in your work piece of the driver blade? If yes then it is most likely jammed nails. If not could be a broken driver blade. If gun does not fire could be gas problem. (check in date, yes it does have a use by date), another cause of not firing is a broken wire particularly around trigger switch (switch is on trigger and hence the wires are flexing every time trigger is pressed). Another cause of not firing is a brass spring clip in handle assy if this breaks it stops the gun firing. Recently I have had more broken wires than anything else on these guns. Worth noting is that the Stanley Bostitch nail guns suffer the very same faults. Also note they are the same gun just different colours so you can fit Hitachi parts to the Bostitch and they are cheaper.

Usually caused by debris in the small air passage from inside of gun to feeder piston. Easy to check. Remove the head and pull out the cylinder. Debris in the chamber is usually small pieces of oring or the lower bumper is coming apart. This debris will enter passage to feeder which is visible at bottom of chamber. If debris is found, clean chamber, passage, and feeder chamber. Debris will lodge on the oring between the body and nose. Clean and replace parts as needed. If the gun was found to be clean inside, suspect weak or missing feeder spring/s. Good luck/

There are several methods for installing this little spring. My simple method. You will need 30 mm x 3 mm roll pin and a small piece of nail about 1/2 inch in length. It is very difficult to install the small factory roll pin so I use a longer one then cut off the access with Dremel. Remove the 3mm roll pin and pull out the lever discarding the broken spring. Fit the new spring on the lever using the 1/2 inch piece of nail that can pass thru the 3mm hole of the lever. The piece of nail should not stick out either side so that you can slide in the lever with short pin holding the new spring in place. Now insert the lever in place on the door and hold in position (temp pin aligned with 3mm holes in door ), lightly hammer in the long 3mm roll pin. The long roll pin will push out the temporary piece of nail holding the spring in place. Once the long roll pin is in place, cut off the extra length. Good luck

Susan Sylvia is exactly right. I just fixed my tool with her information. I would add to be very careful not to disturb the 2 small springs(associated with the trigger and safety mechanisms) and take note of how they are positioned. Also, the screws seem to strip unusually easily so be gentle when removing and replacing them.

If a nail is stuck between the driver and nose of the gun, you will need to forcefully push the driver back into the gun. Remove the head and cylinder and place the body of the gun on piece of plywood with nose pointing up. Using very sturdy steel rod, hammer the driver down. The steel rod needs to be slightly thinner than the driver to allow for the stuck nail. I use a broken driver ground thinner on the side that will need to bypass the stuck nail. Careful when striking hard steel with hammer, could spinter (I use a heavy brass hammer). Good luck

Nail guns will jam when driving nails thru very hard wood, solid objects, allowing the gun to double fire hitting the first nail or using the wrong nails(amoung some of the reasons, you get the idea that jamming is common) . There is no special tool to help in case of jam. You must be creative. I use an old driver shaft from nailer that easily fits into the nose of the gun (you can grind a piece of allen wrench to fit into nose and allow space for the stuck nail). The metel that you use must be very hard and strike with heavy copper or brass hammer (caution, steel hammer may splinter metal, use protective gear ). You will need to strike very hard to remove some stuck nails. If first or second strike results in no movement of driver, remove the head and cylinder of the nailer and place the body of the gun squarely on piece of plywood over concete floor (this will protect the head of the nailer from being damaged). Worst case, you will need to remove the rails. Good luck.

In our shop we have a lot of broken drivers to fit various nailers to use as driver punch.
So that the driver punch does not also get stuck, you must grind the side of steel to allow for wedged nail. Sometimes you must hit the punch very hard. It could crack the head, so if very stuck, remove head and cylinder parts and place body of gun against piece of wood. Not all guns can be saved. Also, hitting driver steel can eject pieces of metal, wear proper protective gear and secure area. After you free the driver, check surface of point for deformation. Good luck

With the staple exit facing toward you (don't squeeze the handle), find the small black square at the bottom (opposite end) from staple exit. Grasp both sides. Pull away from gun (not down). Chamber will open.

If the nails are stuck in the rails, remove the rails and fish them out. If a nail is stuck between the driver and nose of the gun, you will need to forcefully push the driver back into the gun. Remove the head and cylinder and place the body of the gun on piece of plywood with nose pointing up. Using very sturdy steel rod, hammer the driver down. The steel rod needs to be slightly thinner than the driver to allow for the stuck nail. I use a broken driver ground thinner on the side that will need to bypass the stuck nail. Careful when striking hard steel with hammer, could spinter (I use a heavy brass hammer). Good luck

Be sure to remove the metal nose piece that covers the lockout bar when assembled. It may be stuck to the other half of the gun. Replace the bar and the spring and put the metal nose piece in its position over the lockout bar. At this point the metal nose piece will be on the opposite side. This will allow you to replace the 2 halves carefully so as not to loose the spring.