Pulled my barely-used PC RN175 out this evening to do a quick porch roof, and it's behaving in a fashion I've never met in a pneumatic nailer before.

When it fires, it "stutters" afterwards, sometimes for several seconds. It sounds a lot like a machine gun - the piston is cycling as fast its it can. Often the 2nd cycle will pick up a 2nd nail, but almost always after that it isn't feeding additional nails, just cycling the piston constantly. I can't tell if the lack of additional nails (not that I want them, doubles are bad enough) is because the feed isn't advancing, or if the piston is short-stroking after the first/second oscillations.

This isn't bounce - it will keep cycling even if I lift it off the work, and take my finger off the trigger.

Needless to say, this made the quick porch roof, somewhat less than quick.

Any advice on where I start on this?

Many thanks,
Will Ray

And, I had a chance to start installing a re-ring kit in the RN175, and I think I might have found the problem. I don't have the part to replace it yet, but, while none of the rings, or the bumper, show any wear or damage whatsoever, part #116, the "piston stop", is completely gone.

Not "gone" like "in really bad shape", but gone like, there's some little whitish rubbery mushy bits in corners and holes where it ought to be, there's nothing even resembling what the part looks like, in the space where it belongs.

On to finding a replacement!

Will

And that does it. Replacing part# 116, Piston Stop, seems to have corrected the run-on/stutter. (Or, at least seems to - it sounds like there's still a /small/ amount of oscillation that the piston does, before settling down. It's certainly not doing the "pretend I'm a machine gun" dance that it had been previously, but I'm used to the very precise "bang/snick" that my other nailers produce, and this one is now going "bang/snickbbb", not quite doing a dead stop at the top. Of course this could be the nail-feed, so it might be completely normal, just not what I'm used to).

I guess I'm a bit surprised - when I was originally trying to diagnose this, I saw lots of people complaining that a disintegrated piston stop caused their gun to stop firing (piston stuck in the down position), but no references to symptoms like "won't stop running", so I had pretty much ignored that end of the gun as a possibility.

I'm glad I have it running again, but it looks like I've got some not-currently-needed spare o-rings and other bits...

Thanks for your help!
Will