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Author Topic: Benjamin 310 rebuild - home made valve rebuild kit, piston head and bolt handle  (Read 648 times))

Offline happymecanic

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I'm currently rebuilding a nice oldie, a Benjamin 310 of around 1950-51 I think. I started a thread when I began working on it: https://www.gatewaytoairguns.org/GTA/index.php?topic=171647.0

The gun needed to be re-sealed, and altough I could have bought a complete kit with the valve tool, I decided to make the parts. I first made the valve tool, by following these guy's instructions:

 

After the valve parts were out I measured them and started work. I made the new check valve and exhaust valve seals, and valve body seals in teflon. The new poppet stem is made from O1, with a brass cup. I had springs suitable for the application on hand, and the stock separator washer have been replaced by a new one with spring seats with a delrin bushing for the exhaust spring.

I still need to make a new, oringed piston head and the bolt handle, I'll post more pics in the coming days.


Offline xcalibur

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Be aware that the teflon valve guide gasket looks a little thick to me. It might prevent the ports from lining up properly, thus resulting in lower velocity.
Looking good though..carry on.


  • Solsberry, IN
Steven

Offline RBQChicken

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The first time I hit it, I missed. The second time I hit it in the same place.

Offline happymecanic

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New piston head in brass, using generic 9/16'' x 3/4'' x 3/32'' buna orings from the hardware store. Groove size is 0.108'' wide with a 0.586'' diameter on the bottom. I measured the tube ID at 0.770, that gives a 0.003'' compression of the oring. There are flats machined at 5/8'' wide, to use a box end wrench to install/remove the head. Front lip is 0.025'' thick. Tread size is 5/16''-18 NC.

Offline happymecanic

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Re: Benjamin 310 rebuild - new parts
« Reply #4 on: April 16, 2020, 10:12:09 PM »
I decided to modify the new piston head to accept a felt oil wiper, it'll be more useful closer to the oring. I had to re-thread the rod a 1/2'' more, and I used a brass nut and washer to hold the felt (fits well with the gun :D). I also made a teflon guide bushing that goes where the felt was on the piston base, no more metal-to-metal contact. I pushed the piston by hand in the tube, it glides veeeery smoothly  :D. I am now ''over the edge'' of this build, I can foresee the end and I'm getting quite excited about it!

Offline happymecanic

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Today I finished making the parts I'll need to rebuild the 310. The bolt needed a handle, a cocking pin and something to replace the locking ball.

 I suspect the missing original handle has broken off, it had smallish 6-32 threads and I guess was made from mild steel. I made the new one in chrome-moly steel, with 8-32 threads - of course the bolt is re-drilled and threaded accordingly. The cocking pin is made from O1 tool steel. I made a mini plunger to replace the missing ball (funny: about the same size as a 13xx/22xx safety ball  ;D), using a broken drill bit. I chucked it in my hand held drill and ground it using my  dremel with a cut-off disk.

The pump arm also had a hidden issue, a very worn link rivet, with the corresponding hole in the link elongated, and a bent, worn and cracked spring. I made a new rivet out of O1 again. The elongated hole was slightly enlarged and rounded, and a piece of 4140 steel was ''riveted' in place, then ground flush and re-drilled to the correct size (3/16''). The spring wasn't salvageable, so I made a new 5-leaves ''spring pack'' out of an old chainsaw rewind starter spring.

Offline xcalibur

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Nice lathe skills. I can never get the ball on the bolt handle perfectly round. LOL
  • Solsberry, IN
Steven