# Porter Cable FR350A Framing Nail Gun continually leaking air from exhaust port



## Texican57 (11 mo ago)

Air pressure too high?


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## frankpc (9 mo ago)

No. As the pressure builds up from zero psi, air leaks out of the exhaust port. My compressor is just a Porter Cable pancake unit. Air escapes from the nailer's exhaust port slowly enough to allow the pressure of the compressor to slowly build. After the pressure gets to maybe 20 or 30 pounds, I shut off the compressor so that I can hear and feel the air escaping.

thanks for the help!


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## Old Thomas (Nov 28, 2019)

The nail gun needs a quick rebuild consisting of new seals and o rings and any worn parts. If it was done, either it wasn’t done right or a defective part was overlooked. My suppliers used to do it overnight for $25 to $50, depending on what they replaced. I used to have that happen in cold weather if I didn’t warm up my nail guns before using them. O rings and seals would crack or shatter. I had a school bus heater in my step van and I kept my guns by it on the way to the job.


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## frankpc (9 mo ago)

Thank you O. T. 

I'll take the gun apart and recheck the O rings and other parts.

One question: If the trigger assembly is working correctly, is air allowed to bypass it and enter the main chamber of the gun?


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## Old Thomas (Nov 28, 2019)

The air chamber on the gun should be refilled with compressed air after every shot. That compressed air is what fires the next nail. The trigger releases the air stored in the chamber to fire each nail, then the chamber fills for the next shot. The trigger does not fill the chamber, it releases it.


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## frankpc (9 mo ago)

thank you O. T. for the explanation...
Well... I've taken it apart 12 or 15 times. Still haven't found the problem. O rings look good and are well greased/oiled. I've put the new trigger assembly in as well as the original. The O rings on them look fine. Air only leaks from the exhaust port. Truth is... the original parts look OK except for the only broken part, which was the collar. But its replacement fits properly and is in good shape.

I'm out of ideas. Very strange! 
Thanks for the help!


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## ront02769 (Nov 28, 2008)

Rthe my porter cable gun started leaking maybe five years back I took it to local lumber yard for rebuild. Estimate was like a hundred and twenty five bucks. Bought a new hitachi cordless gas powered gun for an extra hundred. Weill going today five years later. In your case you can grab a new metabo brand (was hitachi) or like $175.


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## frankpc (9 mo ago)

Thank you ront... I ended up buying a used FR350B in "good" condition on Amazon for $50. I've only shot 3 ea. 16 penny nails with it for test, but all three worked fine. And no air leaks. Time will tell. I don't know why someone's used FR350B would end up on Amazon. 

As far as my FR350A is concerned, I'd just like to figure out why it leaks air even if I never use it again. A real mystery. The person who borrowed it spent $70 or so buying a rebuild kit and a new collar. Probably more. But even after him rebuilding it and me rebuilding it with new and used stuff too many times, it still leaks air. I don't get it !!!

Thanks again for the advice !!


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## steves7839 (Aug 18, 2019)

frankpc said:


> As far as my FR350A is concerned, I'd just like to figure out why it leaks air even if I never use it again. A real mystery. The person who borrowed it spent $70 or so buying a rebuild kit and a new collar. Probably more. But even after him rebuilding it and me rebuilding it with new and used stuff too many times, it still leaks air. I don't get it !!!


I've been rebuilding used nailers for a few years now. One consistent cause of comeback cap air leaks has been the "head valve". Its function is to seal the cylinder from air pressure except during the firing sequence. Even though it might look intact it may have a micro crack or embedded grit. I've learned to replace them preventatively if at all discolored.


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## frankpc (9 mo ago)

I did replace the plastic piece. Can you describe the appearance of "discoloration" ?

A friend rebuilt the gun. As such I have doubts about the inner O-ring in the head valve. It seems the O-ring that was there initially, was shaped from 'square' rubber. The O-ring that is in it now is a typical O-ring. It seems to seal, but it doesn't appear to be like what the original 'may' have been. Should it be of square material?

Thank you for the help!


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## steves7839 (Aug 18, 2019)

frankpc said:


> I did replace the plastic piece. Can you describe the appearance of "discoloration" ?
> 
> Should it be of square material?



New head valves are translucent white in color. Anything brown, yellow, or with embedded grit on the cylinder mating surface qualifies for replacement. Also check the plastic piece under the head valve spring for the same condition. And verify the metal ‘special washer’ inside the head valve is intact.

Both head valve o-rings are standard Buna-N o-rings with circular cross section.


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## frankpc (9 mo ago)

I have noticed that the O-ring within the head valve piston, which does have a circular cross section, is somewhat scarred. It is the replacement O-ring and it became scarred due to placing the head valve piston into position around the aluminum casting, which has sharp edges. Perhaps scarring the replacement O-ring was enough to stop the attempted repair from being successful.

On the parts diagram for the 350A, the ring that is placed within the head valve piston is stated to be a "quad ring". And from the picture of it, it appears to have a square cross section. Using an O-ring there made the installation of the head valve difficult because it was so tight. That is why I suspected that particular ring should be a "quad ring" and perhaps using an O-ring there made the installation so difficult. 

Do you know whether a quad-ring should be used rather than an O-ring within the head valve piston?

Thank you for the help.


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## steves7839 (Aug 18, 2019)

frankpc said:


> Do you know whether a quad-ring should be used rather than an O-ring within the head valve piston?


I would follow the manufacturer's parts specification. ereplacement parts dot com and many other vendors have interactive drawings, usually with a photo of each part.
My earlier o-ring opinion in post #12 was based on experience with the FR350B.


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## frankpc (9 mo ago)

OK! Thank you for the help. I'll go ahead and buy the quad ring to see if that helps.


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## JLawrence08648 (Mar 1, 2019)

Try silicon grease? Same used for plumbing faucet O Rings.


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