Air nailer - how do i stop large indentation from safety head?

Most nailers have a pressure sensitive safety feature surrounding or near the nailer head. This is so that they won't fire unless pressed against a surface. You may not be holding the nailer against the doorstop head board with enough force to release that safety.

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Air leaking out of head and driver extended indicates that the cylinder seal is bad and or the head valve is sticking or stuck in the head. Easy to check by removing the head and looking at the large plastic seal on top of the cylinder. If seal looks good, pull out the head valve and lube with white grease. Parts are here :

Good luck

If the new trigger valve leaks air when you connect the air supply, most likely defective valve or air is leaking past outer trigger valve orings due to debris in the slot or new orings were cut when the valve was pushed in. If air leaks when you depress safety to fire gun then most likely problem is in the head valve or safety foot is not pushing the firing pin all the way in. Easy test, remove nails and remove the trigger to expose the firing pin. Connect air and very quickly depress the firing pin all the way in. If the gun fires, adjust the safety foot as needed. If the gun does not fire, remove the head and check headvalve orings for good snug fit against the cylinder within the head. The surface were orings make contact must be very smooth and not too deeply worn. If you notice fine scratches remove with fine sandpaper. Reinstall head using plenty of white grease on all the orings within the head and retest. Good luck

Easy test, remove the trigger to expose the firing pin and remove the nails. With air connected very quickly depress the firing pin all the way in. If the gun fires, the safey foot is not pushing the pin all the way in. Make adjustments to correct. If the gun still does not fire, the headvalve orings are leaking internally. Remove the head and pull out the head valve. Make sure that there are no fine scratches on the surface where the headvalve orings make contact to cylinder in head. If scratched, remove with very fine sandpaper. Remove the large outer headvalve orings and wind a couple of turns of teflon tape in the groove and replace the oring. This will make the oring fit more snuggly against the head. Lube with white grease and test. Good luck

To find the model number, look on ebay for hitachi framers and hopefully you will find one listed that looks like yours. If no joy, take the gun to your local fastener/nailgun dealer for parts. The dealer most likely has box full of used parts for your gun. I have seen many older nailers with bent safety foot that caused the plunger to stick in the engaged position. Some nailers have the safety return spring incorporated within the trigger plunger /valve area and still others that have the spring hidden under a guard on one side of the nailer (guard part # 883493). Look under the main body of the nailer for an indention where one side of the safety spring fits into (less than 1/2 inch in diameter) ; directly below the indention will be a point on the safety foot to catch the other side of the spring. Good luck

take of clylinder head when off there is a large button make sure its fre should work like a door bell switch grease slightly and put together again

Remove nails and use thin tool to push driver all the way up to top of cylinder. If the gun fires one nail then skips, the driver is not returning to top of cylinder. If no nails fire, then nails are not feeding into proper position. Driver must return to top to allow nails to feed into position. Most common problems are bent driver, worn piston oring and bad batch of nails(head too large). Good luck

make sure the safety release where the nail comes out is depressed. also check to see if it is low in nails/staples. I have an older nail gun that will stop when it is low on nails

Check the magazine area near the head for a jammed nail or other feed obstruction. It sounds like the driver is hitting the wood ok. Did you change nails (brand, type, or size) when this occurred? Make sure the magazine feed spring is ok.

There is a large diaphram inside the nailer (inside) that is out of place or damaged.

Remove the 4 screws to access the diaphram and inspect it.