Repairing a dry fired FX

[CableStop]

So I messed up... I fired my Dreamline without any air in it and ended up screwing up the valve.  Basically without air the valve can over travel and the hammer can collide with the back of the valve which deforms the valve stem hole and prevents the poppet from closing all the way.  The valve is machined into the breech itself which means you can't just replace it if something goes wrong, it also makes it difficult to reach in order to repair it. 

I ended up making a lapping tool long enough to reach the valve stem hole by turning down the end of a quarter inch steel rod to match the 0.143" valve stem diameter, my tool actually tapers from 0.142" to 0.150" but it worked fine.  I chucked it into a drill and started with a multi-grit engine valve lapping compound then moved to 5k grit diamond paste.  I spun it both direction with moderate speed and pressure, it only took a few seconds with each grit to get a fairly smooth finish, cleaning the breech afterwards was a pain though. 

I can't understand why, for the money, they can't include a PEEK striker on the hammer to prevent this from happening. Anyway I included a picture of my lapping tool below.

[mr007s]

oh man, thats a bummer

[CableStop]

oh man, thats a bummer

The lapping fixed it, I've shot 3 mags tonight since the repair and it works fine.  McMaster-Carr also sells 0.143" rod which would be a good solution for people who need to make a lapping tool but don't have a lathe. 

[rkr]

So basically if you are Joe Average and if you happen to dry fire a FX you'll ruin the breech block and need to buy a new one?  Well done fixing it, that method may become useful one day.

[Mr.P]

I thought these were premium engineered guns... what's the appeal?

It sounds like they should issue a recall.

[sb327]

If I’m understanding the issue correctly, a simple chamfer at the start of the hole would have avoided the issue. But it may not be that simple.

Even if I were to put a soft hammer face in there, I would still want to dress the hole.

Good save without making anything worse. 

Dave

[CableStop]

I stumbled upon one of motorheads old posts describing the problem which is why I gave it a shot. I could have sworn there was a countersink in the back of the valve but it's hard to see clearly down into the breech. There was definitely a burr inside the hole when I looked closely though.

This was my first time trying to fill it so maybe the burr was left over from manufacturing but that seems like an awfully big coincidence.  Plus that'd mean no one tested the rifle to see if it filled before it left the factory. 

[rsterne]

Seems like a countersink on the back of the valve would avoid the problem.... 

Bob

[mrbulk]

I stumbled upon one of Motorhead's old posts describing the problem which is why I gave it a shot.
 

I am thankful we have such accomplished airgun technicians here who gladly share their experience and knowledge.

There is a reason why many Intro posts in the New Members section start off by saying they came here for the knowledge.

[killahog]

I thought these were premium engineered guns... what's the appeal?

 Dry firing with air in the cylinder will not cause damage . It’s unfortunate that occasionally mistakes are made and they are dry fired when empty. However the majority of the time the guns will have air in them and will not be a problem

It sounds like they should issue a recall.

[CableStop]

Just to make it clear I screwed it up, I've talked harshly about FX before but this isn't really one of those times. Had I actually read the manual I'd have known not to fire it empty.  I just wanted to post the fix I came up with incase anyone else ran into the same issue. 

[CableStop]

Ironically I'd already been working on an aftermarket hammer for FX guns when I figured out this was my issue. Here is my second version of an aluminum/PEEK hammer, the brass insert/PEEK striker are pinned into the aluminum body to keep them from moving backwards.  Weighs a little less than stock but I'm hopefully going to fix that in V3.

[rkr]

Just to make it clear I screwed it up, I've talked harshly about FX before but this isn't really one of those times. Had I actually read the manual I'd have known not to fire it empty.  I just wanted to post the fix I came up with incase anyone else ran into the same issue. 

There's a fair share of consumers who never bother to read the user instructions, I work with such issues daily and I'd say the number is well over 10%. If I was running FX as a product I would fix the problem and not rely on user instructions in preventing problems.

[RDB]

. I believe RAW states not to dry fire without sufficient air. As does Edgun. At least the used to on the leshy.

You have a hardened hammer smacking the back of a brass valve in most cases. Valve springs can go coil bind and destroy poppets or bend valve stems.

Lesson learned.

[rkr]

. I believe RAW states not to dry fire without sufficient air. As does Edgun. At least the used to on the leshy.

You have a hardened hammer smacking the back of a brass valve in most cases. Valve springs can go coil bind and destroy poppets or bend valve stems.

Lesson learned.

BSAs take dry firing without problems and IIRC so do Evanixes, it's a matter of valve design. You can't assume people to know not to dry fire even if they have owned PCPs before. Even if they do know it may still happen accidentally so I'd design a valve that can be dry fired.

[pdxFrank]

Ouch.  One can't dry-fire an FX?  Ugh, that's unfortunate.  Yet another reason to not want that ugly gun.

[sb327]

Not being able to ‘dry fire WITHOUT air’ is not uncommon. The Airforce tx2 without valve spring has been known to launch the poppet (press fit on stem) into the tank when no air pressure is present.

I have never been one who felt dry fire capabilities to be a requirement. It is a nice thing to have for tuning/trigger adjustment etc. but not a game changer.

Dave