Idiots guide to classic airgun strips (pt 1)

[Phil Russell]

CHINESE B5-3, maybe also known as the B45
I have a .177 version of this pneumatic pump up, 12 shot rifle from an auction bundle several years ago. It did not work; not a whimper. Fairly recently I was given a .22 version, again not working. This spurred me on to have a look at them. I did find an exploded diagram on the web but I admit it was not that much help. The action is not difficult to get into:
Remove stock; a screw at the trigger guard and another at the forend. Lift stock away but catch the trigger spring that sits in a recess. You won’t lose it as it is about 4cm long x 6mm diameter.
It took me several strips to find the easiest route to the bits. It helps to clamp the rifle in a padded vice but this is not absolutely necessary. There is no need to remove the pump assembly unless you are sure the pump is faulty .. if you need to do this, first remove the two small screws in the barrel end cap / sight unit. Then look at the cross bolt that goes through the cap. One of the screw heads will be a ‘keeper’ that screws into the end of the cross bolt. Remove it ,,, it is a 3mm thread … then drift out the cross bolt and remove the end cap. The pump handle is now free and you can pull the pump assembly out of the cylinder. I am not sure what you can do if the pump head is faulty as I do not know if spares are available. The head is a screw on type and it is possible that a unit from a Crossman could be adapted to fit. Re-assembly is a reverse of this. Add a lubricant … Pelgun oil.
With the action in the vice, trigger to right, there is another cross bolt at the rear of the action. This holds the hammer in place and there is no need to remove it unless you want to. To do so, remove the cross bolt, ‘keeper’ screw as before and the hammer mechanism will pop out a short distance. Pull the end block out, followed by the hammer spring and the hammer block. Note the groove in the end block; the cross bolt passes through this to keep the unit in place.
To access the valve, note the two screws alongside the 12 shot rotary magazine. Remove one of them .. each about 8mm long and then remove the other while holding the magazine in place. As the second screw releases the magazine housing will move back a little. Carefully remove it and catch the steel ball (about 6mm?) and the spring that sits in a hole in the action.
Look inside the action and note a retaining nut with a slot on each side. This needs undoing; I used some small needle nose pliers; easy. Remove the nut.
The valve unit parts can now fall out. Remove in order: a steel washer and the exhaust valve body that has a steel rod through the centre. Working from the barrel end, this valve body has a flat rubber valve seal on the rod, followed by a small steel washer and O ring around the rod. The washer and O ring sit in recesses in the valve body.
It is quite likely that the inlet valve has stayed in the action… pull it out gently. There will be a spring with a captive end piece and flat rubber valve seal.
On my rifles, various combinations of the valve seals and O ring needed replacement, quite clear by the splits present. Not being able to get original seals, I made some from 2mm thick rubber sheet. The inlet valve seal is 11mm diameter (wad punched) with a 1.5mm hole (leather belt hole punch) in the centre. It simply pops over a small peg on the captive end piece. The exhaust valve seal is 14mm diameter with a 5mm diameter central hole for the steel rod to pass through, again wad punched. My first attempt had the central hole slightly too small and it gripped the steel rod too tightly leading to a failure of the valve to work. The O ring in the valve body is, I believe, BS008.
To reassemble, drop the inlet valve and spring into the action, spring uppermost. Assemble the main valve body with the exhaust valve seal on the end of the steel rod, then the steel washer and the O ring. Put the steel rod through the valve body, making sure the O ring and small washer locate in the recess. Insert this unit into the action and add the large steel washer followed by the retaining nut; tighten the nut.
Place the magazine spring in the action hole followed by the ball then seat the magazine on top. Add the hammer housing and secure it with the two bolts. If you removed the hammer components, add the hammer, spring and end cap. Make sure the groove in the end cap allows access for the cross bolt; add the cross bolt and retaining screw. Replace action in the stock, do not forget the trigger spring and add the two stock bolts.
One of my rifles had an extra surprise. On top of the action was a threaded hole; examination showed it went down to the transfer port area. The other rifle had a screw plug fitted. I added a screw plug to this rifle. There was a similar hole on the underside of the action, this one clearly designed for a countersunk head screw. Again I plugged it. I have no idea what these holes are for.
This should be job done. From non working rifles, both mine are now healthy and three pumps gives a hearty crack as the pellet flies into the backstop. I have not tried four pumps or more as three seemed adequate effort.

Cheers, Phil