Tools needed  

Flathead screw driver or
square drive
Allen wrench 0.050
Phillips screwdriver
Roll pin punch
3/16 drill bit or rod
Hammer
Wood dowel ½”
Sand Paper

1. Remove roll pin front sight-barrel band assembly,

2. Remove pump arm linkage and pump assembly.

3. Remove rear sight assembly

4. Remove 0.050 allen screw, breech & barrel assembly, exhaust port tube & seal

Note:
The exhaust port tube has a top and  a bottom note the tapered side and flat side

5. Remove front pistol grip screw

6. Remove rear pistol grip screw & pistol grip assembly, rear tube plug & hammer spring.

 Note:
When removing pistol grip from the pump tube there will be a small spring and check ball,  this is what holds the safety in the on or off position , be careful not to loose they are very very small.

You can leave spring and ball check in the pistol grip if you are replacing only the piston and valve.

7. Consist of the hammer & hammer cocking pin. The hammer must be slid to the rear of the slot to the hole then the pin may be removed by pulling straight up and the hammer will slide out of the tube.

 8. Use the wood dowel to push the stock valve out of the tube from the back of the tube
 (rear sight end) to the front (front sight end)

 Note:
Make note of the exhaust port and threaded hole (top & bottom) the new valve must line-up with the tube when you reinstall the valve in the tube. Exhaust port on top threaded hole on the bottom

 9. Clean all burrs from inside of tube with fine sand paper wrapped around the wood dowel (fine sand Paper) clean all grit from the tube.

 10. Install the new valve, note the exhaust port and threaded hole, Exhaust port on top threaded hole on the bottom flat side to the front valve pin to the rear

 Push the valve in with wood dowel line up the holes on top and bottom. 

11. Assemble gun in reverse of tear down except piston, linkage and pump handle. 

Adjusting the piston:

1.      Piston Top
2.      Bushing
3.      Knurled Lock Ring
4.      Stud
5.      Oil Wiper
6.      Piston Bottom
7.      O-Ring

This is where the 3/16 drill or rod will come to use
 

1. Remove the O-Ring
2. Oil the pistons oil ring/wiper (5)
3. Loosen (3) Knurled Lock Ring and shorten the piston as short as it will go use only your fingers.
4. Remove stock piston from the pump linkage and measure up the stock piston and the flattop piston get as close as possible to the same length.
5. DO NOT install O-Ring yet

5. Attach Flat top piston to the pump linkage with the piston pin then slide piston into guns pump tube  install barrel band front sight assembly using the drill bit slide through tube, barrel band and linkage to temporally hold the  gun together, gently close pump lever until you feel the pump touch the piston. There should be only about 3/4s of an inch, or 19 to 20 millimeters gap between the pump handle and pump tube this will allow the piston to squeeze out maximum air pressure and then to cam over to hold the pump lever closed on the tube. After you get this correct go to 6
6. remove piston from tube snug lock ring test one more time by following step 5
7. install O-ring
8. Reassemble gun and button it up with roll pin.