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Benjamin model "C" restoration

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Garvin
(@garvin)
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Joined: 6 years ago
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Benjamin model "C" restoration 

With thanks to Mark.

He said:

I have recently restored a Benjamin Model C and had been working on a post outlining the steps I took, but it was too big, and I needed to upgrade to VIP to post it.  The gun needed a lot of work to get it resealed and holding air. This old gun now shoots with such authority with two pumps that I can't help but think it shoots as it did when it was new.  If you have an old Model C that you'd like to get shooting, keep reading. I have added content below to this post on what I did to get mine shooting again.





 

He continued:

The Benjamin Model C has a unique design that includes an air tube with a cup on the end on which sits a rubber ball to seal the air chamber.  There is a brass firing pin that has a cupped end with a point that sits on top of the rubber ball.  This pin must be inserted from inside the air chamber. You will probably want to remove the firing pin, depending on what type of work you are doing and the position of the barrel.  

These old air guns can leak air from the rubber ball seal, air tube, or the air chamber plug.  I will discuss how I addressed each of these in following posts. Please be aware that these are the steps I took, and while I got mine holding air and shooting, I can't guarantee it will work for anyone else's Model C. You may have a better or easier way to complete some of these steps, so comment if you do. 


The air chamber plug may be old and dried out. I have seen rubber and cork plugs in these old guns. If the plug is hard and dried out, you should make a new plug.  For a tight fit, make a 7/8" diameter plug about 3/4" thick. You can lubricate the plug with Vaseline to help push it in and help it come out. 

Gasket Punch Sets are readily available on Amazon.  Rubber plugs available at most home improvement stores like Lowes and Home Depot.  

Now let's discuss the rubber ball. The original rifle probably came with a rubber ball, but how pliable were they? A 3/8" or .375 diameter ball works. You can purchase rubber balls from McMaster Carr but the balls that worked for me were 50 Duro Silicon Balls from Precision Associates, Inc.  PAI sent me a sample pack for free. The ball needs to be pliable enough to conform to the cup and outlet flange to provide a good air seal. 

The air tube is a rolled tube with a seam that can open-up over time.  The cup must be removed to access the air tube. This can be done with a heat gun to break the original solder joint.  Once the cup is off, you can use 1/8-1/16" heat shrink tubing to seal the air tube. Slide the shrink tube over the air tube and cut it to proper length. You will want to cut it 1/16" short to leave the end of the tube with exposed metal for the cup solder connection. Use a heat gun to shrink it.  You may need to seal the base of the tube with an epoxy like JB Weld.  You can use an artist's paint brush or Q-Tip to get down to the base of the tube. The air chamber is approximately 4-inches deep, so you need something long enough to reach to the bottom of the tube.  

Once complete with epoxy cured, put the pump rod in and while holding your finger over the end of the air tube, try to push air in. You can also secure the air chamber in a vertical position and put water in it. Hold your finger over the end of the tube and try to push air in. If you have no bubbles or obvious air leaks, you have a good seal and can proceed to reattaching the cup.


If the tube is deformed and cannot be straightened. remove it. you can twist it out and then drill out the part that remains at the base. You can purchase a 3mm brass tube on Amazon. This tube is a machined tube with no seam. It is 300mm long. All you need is approximately 75mm, so you have enough extra left over if a mistake is made. You can use a stiff, small wire to position the air tube straight in the air chamber. You can stick a wire or small nail through the firing pin hole to mark the tube for where to cut it.

You will need to solder a washer at one end with approximately 1/8" extending below the washer. This washer is to keep the tube from slipping through the hole into the pump chamber.  Make sure the tube is cut to the proper length because too short or too long will not align the cup properly with the outlet flange.  The end of the air tube should be 1-15/32" (37.17mm) from the back end of the air chamber where the breech cap goes. 


Once the tube is cut to proper length with a washer soldered to one end, you are ready to install it in the air chamber. Use a long, stiff wire from the pump chamber side, or use a wood dowel rod with a shorter wire to go through the air inlet port and up through the air tube.  Ensure it is straight and secure it in-place.  The air chamber is 4-3/32" (104.13mm) deep.

Ensure the washer is flat against the base of the air chamber. and the air tube is straight and aligned center of the outlet flange. Use an epoxy like JB Weld to seal and secure the tube at the base. Use an artist's paint brush or Q-Tip to apply around the base of the tube.  Allow sufficient time for the epoxy to cure and then remove the wire support.  Conduct another test as described above to ensure you have a good air seal.  Once confirmed, you are ready install the cup. 


To install the cup, make sure the cup and the end of the air tube are clean.  You may choose to install the firing pin before reattaching the cup, but it can be put in afterwards.  Use a solder paste like ChipQuik that can be purchased on Amazon.  Use a Q-Tip to apply some solder paste to the end of the tube. After this, extend a stiff wire through the air tube to clear solder paste and use the wire to align the cup. 

Apply solder paste on the cup at the tube hole and use needle nose pliers to align the wire through the tube hole. Push the cup in to mate with the end of the air tube.  If you can retract the wire and the cup stays in-place that's good, but if the wire must stay in place, be aware that the wire could be soldered in-place. Take precautions to avoid this.  Make sure the cup is aligned square with the outlet flange face. Use a heat gun to resolder the cup to the air tube. 


Allow the solder joint to cool, and use the pump rod to push air through it. You should have unobstructed air flow. If not, you may have solder blocking the air.  If so, use a heat gun to remove the cup and try again. 

If air flow is clear, test to make sure the cup's solder connection is solid by gently pulling on the cup and pushing it up or down.  Once you have confirmed the cup solder joint is holding. you are ready to reassemble the rifle.  

Install the firing pin, ball, and then the spring under the cup.  

Install the rubber air chamber plug and use the pump rod to push air in. If the rubber plug starts getting pushed out, you know you have achieved a good seal. Install the metal washer, trigger, and breech cap. 

You should have a good shooting Model C at this point! 

He added:

I wanted to add a couple of other tips that may benefit some of you. One is you can use a 3/4-inch Wood Dowel (available at most home improvement stores) with a shorter wire to come up though the pump chamber to hold a new air tube straight.  Another tip is to use a free-standing flexible light with a magnetic base (available through Amazon) to light-up the inside of the air chamber so you can better see what you are doing. 



   
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