Benjamin 312 RestoMod

[Tack Driver 10]

Picked up this 312 earlier this year from a GTA member.
It's in pretty good shape with a nice stock.

The pump link has issues along with the safety.
The pump arm walks out every few seconds so the check valve is leaking.

Took the gun apart and cleaned the parts.
The internals look good with no surprises.
I could just replace the check valve and put it back together but.....

The plan is to replace the heavy spring in the valve with a lighter spring and make a new valve seat.
The seat will have a concave seal and Delrin stem.

It'll be similar to the 317 valve mods done earlier.
https://www.gatewaytoairguns.org/GTA/index.php?topic=160425.0

[Tack Driver 10]

Made a new check valve from Teflon.
Set it with a brass plug and dowel.
The brass plug is similar to a PA.

This is a test version to see if the gun seals.
Put the gun together and it sealed fine.

Next need to replace the heavy spring in the valve with a lighter one.
Not sure if I'll make a new valve seat or leave it stock.

[OTmachine]

Always good to see a highly skilled mechanic at work.  Thank you for sharing!

[Tack Driver 10]

Decided to utilize the stock valve seat for now.
Why recreate the wheel when you can just put a new tire on it....LOL

Turned some #22 drill rod down to .125" and pressed on a Delrin blank.
Machined it to .250" diameter and cut the stem seal with a contour to match the valve seat.

Temped it in the gun to see if it would hold air and it did.
I'll let it sit overnight before it gets the thumbs up.

[Tack Driver 10]

The gun held air overnight so put it together and ran it over the chrony.

With 14.3 CPHPs
03 pumps 402 FPS 5.13 FPE
05 pumps 473 FPS 7.10 FPE
07 pumps 524 FPS 8.72 FPE

Respectable numbers.
Next I'll open up the front end and pull the piston.
Felt like the gun had a lot of dead air when pumping.

[TerryM]

  I imagine a new pump seal will bring the velocity up a bit.

[Tack Driver 10]

Pulled the piston, seal looks pretty good.
This gun must have spent a lot of time in Seattle because there was a ton of grunge in the felt oilers....LOL
Soaked them in mineral spirits and then a stimulating bath in the ultrasonic cleaner.
Now they're squeaky clean as a whistle.

The pump link is the biggest challenge on this gun.
Looks like a gorilla with a bad attitude got a hold of it....LOL
No problem, I picked up a like new replacement earlier this year.

Put a test piston and seal in the gun to see what it can do.
Same test piston I used on one of the 317s.

[Rob M]

looks awesome !

[2K1TJ]

Impressive looking work, as usual!

Curious why the holes in the face of the piston seal? Won't that create necessary head space?

[Tack Driver 10]

Impressive looking work, as usual!

Curious why the holes in the face of the piston seal? Won't that create necessary head space?

Good question which was brought up with the 317 I worked on recently.
https://www.gatewaytoairguns.org/GTA/index.php?topic=160425.msg155787521#msg155787521

The pump link would never support a highly efficient gun building 2000+ PSI with a FT setup.
It would bend like a wet noodle so best to incorporate some dead air to provide some cushion for the pushing.
Also the pump tube will flex and the solder joint between the tube and barrel will fail if pushed hard.
This gun is a 53 year old classic that is best improved with modern materials to hopefully last another 47 years.
That would make it 100 years old in 2067.

[2K1TJ]

Impressive looking work, as usual!

Curious why the holes in the face of the piston seal? Won't that create necessary head space?

Good question which was brought up with the 317 I worked on recently.
https://www.gatewaytoairguns.org/GTA/index.php?topic=160425.msg155787521#msg155787521

The pump link would never support a highly efficient gun building 2000+ PSI with a FT setup.
It would bend like a wet noodle so best to incorporate some dead air to provide some cushion for the pushing.
Also the pump tube will flex and the solder joint between the tube and barrel will fail if pushed hard.
This gun is a 53 year old classic that is best improved with modern materials to hopefully last another 47 years.
That would make it 100 years old in 2067.

Makes perfect sense. Always wanted one, but never ran across one at a decent price.

[Tack Driver 10]

Ran the gun over the chrony with the test piston and new pump arm.
Previous results in ( ).

With 14.3 CPHPs
03 pumps 426 (402) FPS 05.76 (05.13) FPE
05 pumps 528 (473) FPS 08.85 (07.10) FPE
07 pumps 602 (524) FPS 11.51 (08.72) FPE

Was able to straighten the original pump link, good pump link for an everyday shooter.

[TerryM]

  Very nice work and nice gun!

[avator]

Ron... That gun really looks familiar. You got it in the exact condition I received except for that safety. I assure you that it wasn't like that when I packed it (presuming this is the gun you got from me). Either way, I'm glad it's in your hands and will get what it deserves. I've followed many of your builds. Looking forward to what you do with it. And yes, the wood was surprisingly nice. IIRC, it looks like at some point someone had a butt plate screwed onto it the plugged the holes..... my memory ain't what it used to be.

[Tack Driver 10]

Ron... That gun really looks familiar. You got it in the exact condition I received except for that safety. I assure you that it wasn't like that when I packed it (presuming this is the gun you got from me). Either way, I'm glad it's in your hands and will get what it deserves. I've followed many of your builds. Looking forward to what you do with it. And yes, the wood was surprisingly nice. IIRC, it looks like at some point someone had a butt plate screwed onto it the plugged the holes..... my memory ain't what it used to be.

Right, that was your gun.
The main reason I like this gun is the stock was so nice.
I see a lot of these guns where the stock has been beat up or has cracks etc.
I don't think the stock had a butt plate as seen in the picture.

I see a lot of the 317/312 guns with the safety tab broken off for some reason.
Not the best design and best taken off and decock/cock the gun instead.

[Tack Driver 10]

Since I was able to straighten out the original pump link it was time to replace the rivet.
Obviously I'm not the first person to work on this pump link.
The existing rivet was very hard so had to grind it out.
Best to use a mild steel that can be drilled and hammered.

Took an 8 penny nail and turned it on the lathe to .130" x .290".
Set it with a hammer and center punch.
Previously when pumped the arm would make a snapping sound due to the loose rivet.
Gun pumps nice and smooth now.

I guess you could say I nailed it?....LOL

 

[avator]

Like I said.... memory ain't what it used to be.

[Tack Driver 10]

Like I said.... memory ain't what it used to be.

My memory is so bad that I can't remember if I ever had a memory....LOL

[desertplinker]

Since I was able to straighten out the original pump link it was time to replace the rivet.
Obviously I'm not the first person to work on this pump link.
The existing rivet was very hard so had to grind it out.
Best to use a mild steel that can be drilled and hammered.

Took an 8 penny nail and turned it on the lathe to .130" x .290".
Set it with a hammer and center punch.
Previously when pumped the arm would make a snapping sound due to the loose rivet.
Gun pumps nice and smooth now.

I guess you could say I nailed it?....LOL

 

Ron you do nice work, wish I could do half of what you do. I bought a tootsie roll 342 on a whim, it holds air and the wood isn't bad, but it's dirty inside. I don't have the where with all to tear it down, I could make you a very sweet deal, would be nice to see it get your treatment and would be yours to do as you wish.

[Rob M]

Ron , I once resealed a buddys 342 i believe.. anyway , that pivot area was also elongated, almost like it was meant to be that way.. It would click like a ratchet mid stroke.