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Rebuilding a Air Gun (spring piston type)

For those of you that are "do it yourselfers" and are handy with hand tools, here are step by step instructions on rebuilding a spring piston air gun by replacing the main spring and the piston's seal.

The first thing you will need is a "Spring Press", down below is a spring press I made out of a 45 inch long 2x4 wood board.  Other materials I used were a 8 inch C-Clamp, which I placed on a 12 inch 2x 1 inch board and I screwed it to the top of the 45 inch, 2x4 with 4, 3 inch screws.  Notice I cut the end of the C-Clamp and drilled two holes for placing 2, 2 inch screws to screw it to the 12 inch board.  I also used a 4 inch piece of 2x4 on the other end, secured it in place with 4, 3 inch screws and a 4 inch,  2x 1 inch "V" grooved piece of wood in the middle, to secure the air gun to the press, I  also screwed it in place.  After finishing the spring press, I used a wood sealant  to paint it, this well help in the future for cleaning off oil, tar, grease off the spring press.

Below you will find some different types of piston seals.  The leather piston seals are often found in break barrel spring piston air guns, it comes with 2 sections of leather and a screw in the middle.

The B-3/B4 piston seal is a cup shaped silicone/rubber like material that is made for these models.  It goes on top of the piston and covers the head of the piston.  A air gun kit is sold that comes with spare parts, main spring, seals, cleaning rod with oil and the kit comes with these seals.  

Notice I placed 2 water hose gaskets, they are the rubber type gaskets that go inside the water hose.  These rubber gaskets can be used as a piston seal, instead of the factory seal and work well.  I decided to do a test to see if the power of the rifle could be improved.  I have even found that when I  replace the hose gasket for the original seal, it makes more space in the chamber for more pressure and the B-3-1 tends to shoot stronger than before, I believe the air gun gains about 50 fps, maybe more fps.  But I find that it makes more noise because the hose gasket does not cushion the impact of the piston, thus the piston strikes metal with metal.  This is not a recommended method of replacing a piston seal, it could damage the piston's head and the chamber with in time,  but it does work.  

In the photo below, I have taken off the stock and I am using a 3 inch C-Clamp to release the pressure created by the 2 springs on the sliding cocking device in the B-3-1.  After taking off the pressure I  slowly unscrewed the screw that held it in place taking care that the springs do not pop out by placing my other hand on top of the device.  If the springs pop out, they are very hard to find, they bounce all over the place.

In the photo below, I have released the pressure of the main spring using a 3 inch C-Clamp and I have taken out the main spring pin using a pin punch, it should come out easily. I have also taken out the sliding device and the 2 spring cocking device.  Then I took out the pins in the trigger assembly and I  pulled the trigger out  side to be able to take out the main spring and the piston and it's chamber.

Now in the photo below we can see the main spring and the spring piston and it's chamber disassembled.  Notice the plastic spring holder on the right of the photo, from here came out the main spring's holding pin.  Also notice the piston, I have taken off the old dry rotted/damaged seal and I have replaced it with a rubber water hose gasket.   I stretched the rubber gasket over the head of the piston into the seal's holding slot of the piston's head.  Then I tested it and I found that it was bigger than the chamber and did not fit, so I sanded the rubber gasket down with a piece of 220 sand paper  in a round motion twisting the piston with the gasket on it to insure that it sanded evenly until it came to a tight fit in the chamber.  After insuring a tight fit, I placed a little of "Slick 50" oil treatment to the gasket and the chamber and it enter easily in the chamber.  If you have to replace the chamber's/barrel's seal, just pull it out with a small flat head screw driver and with your thumb push in the new one.

Notice that I have placed the old and new spring together.  You can see that the old main spring is shorter than the new main spring.  It looks like this rifle was cocked for a long period of time and squeezed the main spring down and bent it a little.  It either must be replaced or bent back in shape and pulled to the original size and be tempered again.  (see spring tempering in the index)

In this .22 cal. B3-1, since the main spring had no damage to it, we decided to pull the spring out and bend it back in shape and re-temper the main spring.  We pull it out just 1/4 of a inch longer than the new main spring, in other words we made it bigger than it was originally, before tempering it.  The reason being we wanted more power, for the extra chamber space we now had with the water hose gasket as the piston's seal.  The original B-3-1 piston seal is cup shaped and in the front has a thick 1/4 inch thick rubber cushion, replacing it with the water hose gasket, gave us 1/4 of a inch more of pressure space in the chamber. 

Putting it back together is a reverse process, just remember how you took it apart and put it back together again.

After we finished we tested this modified .22 cal. B-3-1 and found that it shot better than a new B-3-1 in .22 cal. over 50 fps more, I would say about 750/800 fps.  Remember, using a water hose gasket as a seal is not recommended, but it will give the rifle more power.  But it might crack the piston's chamber with in time, after all it is metal against metal hammering away.

As I said I modified this B-3-1 as a test, later on I will replace the water hose gasket for the original piston seal before something happens to the chamber, but for now we are having loads of fun testing it. To get your B-3 for less than $20.00, click on the "Air Gun" banner below.

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For all brands of super powerful discount pellet air guns, paintball guns etc.,  scopes, hunting supplies try "Eddie's Super Cool Discount Stuff", we also have a full line of outdoor gear.