Idiots guide to classic airgun strips (pt 1)

[Phil Russell]

Part 1: The strip

ORIGINAL / DIANA MODEL 50 Strip and rebuild
Much also applies to the Model 35 break barrel

These notes are designed to help you strip and rebuild the Original Model 50 underlever rifle that has the feared ball bearing trigger. Much of the notes also apply to the Original Model 35 that has the same trigger assembly.

Strip:
Remove fore and rear sights.
Remove action from stock. There is a simple bolt in the trigger guard. The front of the stock is held to the action by a nut that fastens to the underlever catch. This is a round nut with cut outs in the rim. It is possible to carefully use a small screwdriver to turn this but I made a simple tool to fit over the underlever catch and turn the nut. The cross bolt through the action is also the underlever pivot bolt and holds the underlever in place. Action is now free, as are the underlever parts; underlever and cocking arm.
Remove the loading tap. Not absolutely necessary but makes life easier later as if left I found it interferes with my homemade spring compressor. Press down on the tap plate as you release the 2 screws as there is a spring laden ball underneath. Just release carefully and it will be OK. Do not lose the shims on the tap.
Remove the small barrel cover. This may be held by a small spring pin but I have seen rifles where the pin is missing.
Remove the action end cap.
FOR INFORMATION: Look at the end of the action. Note the inner circular sleeve about 15mm diameter inside the end of the action and the smaller (about 5mm) round object behind the sleeve and at the top of the action. The 15mm sleeve is the part that holds the 3 ball bearings (4.75mm ). It is about 5 cm long and locates against the spring guide. It is held in place by 2 cross pins through the action. Do not remove these yet! The 5mm round object is the end of a spring laden prod.

I now find it best to put action in a spring compressor, barrel to the left and trigger up.

The trigger needs to be removed. I find it best to drift out the trigger pin with a drift then, while holding the trigger in position, carefully remove the drift, so releasing the trigger and its spring.

You now need a socket or other implement that can be used to hold the 15mm sleeve firm while you drift out the 2 cross pins that retain the outer and inner sleeves in the action. The pin towards the barrel is smaller in diameter and acts as a guide, the other pin is larger.
Now carefully release pressure on the spring and let the sleeves be pushed out. As the inner sleeve comes out it will bring the smaller 5mm ‘prod’ out (that you saw above) complete with spring. Also coming out will be another sleeve (the outer sleeve) that fits inside the main cylinder. Try to keep these bits in their original orientation ... I place my left hand underneath them as they come out under the preload pressure, which is not great, about 5cm. Note that the 15mm sleeve is formed from rolled sheet and has the join uppermost i.e. in line with the trigger slot. The uppermost part of the outer sleeve is cut away towards the stock.
Remove these bits. The 3 ball bearings are found in holes in the 15mm sleeve at the left end.
The prod will fall free ... a prod and a spring about 4cm long.

The mainspring, spring guide and piston can now slide out.

Service as appropriate. The ball bearings are standard cycle size. I have seen triggers work with only 2 bearings in place but do not recommend this.

Part 2, the rebuild, in the next thread.

Cheers, Phil

[Phil Russell]

Part 2, the rebuild:

ORIGINAL MODEL 50 REBUILD.

Rebuild:
Nothing to fear really, but a bit fiddly at times.
Put action in the compressor, barrel left, trigger slot uppermost.
Replace piston, mainspring and spring guide. Make sure the piston is positioned with the underlever cocking arm slot uppermost.

Insert the large sleeve into the cylinder about 2cm, the cut out uppermost and pointing towards the stock end of the action.
Assemble the sleeve and 3 bearings ... a dab of grease in the bearing holes keeps them in place. Bearings fit in the holes from the outside. Insert this sleeve into the action, with the ‘join’ uppermost. Locate it against the piston sleeve. The spring and prod needs to be fitted but I found it easier to do this later.

With the socket against the 15mm sleeve, compress the sleeve into the action. This does not automatically move the outer sleeve in so I found it best to carefully move the outer sleeve in by hand (it is not under pressure).
Push the small sleeve in until to cross pin holes are aligned.
It is now time to fit the prod and spring.
I used a short length of cycle spoke to help ... put it through the left cross pin hole and release tension on the compressor. I expect the spoke will bend a bit at this point.
Now turn the action upside down so that the trigger slot points down.
Take the prod and spring and insert the spring over the top edge of the inner sleeve. You may need to lever the sleeve down a bit (hence the freedom to do this give by the spoke) to get it started. Feed spring and prod in as far as they will go. The raised lip of the prod now needs locating behind the rim of the inner sleeve. Push inner sleeve down while pushing the prod in. It will click into place.

Tension the main spring again using the socket. I now insert a drift, or if possible, the correct cross pin through the first hole before removing the spoke. If it is not possible to fit the first cross pin because of slight misalignment, use a suitable drift and then remove spoke and add another drift. It should now be possible to jiggle the alignment Ok by adjusting tension on the mainspring. Fit front cross pin, and then the second pin. You can release tension on the socket.
Turn action again so that the trigger slot is uppermost.
Fit the trigger by replacing its pin but without the spring.
The spring now needs to be fitted. A bit fiddly as it is quite strong.
With trigger fitted, use a blunt screwdriver to push the ‘outer sleeve’ down the side of the trigger so that the trigger engages. This gives a little more room to add the spring.
Locate spring on the nib on the action and compress spring so that it fits over the nib on the trigger blade. This is fiddly. I find it best to use a flat blade screwdriver, using the flat of the blade to push on the spring while I then nudge the spring into the trigger housing. Take care and all will be well.

That’s it .. hard part over.

All that remains is to replace the loading tap ... remember the little ball that sits on the spring in the tap. Replace the barrel cover bit and then locate the underlever into the action before feeding the stock over the lever. Refit the round nut over the underlever catch and refit the through bolt on the stock, making sure it passes through the underlever. Refit the rigger guard bolt. Refit sights.

Job done.
As I hope you will see, the ball bearing trigger is not too difficult. It is possible to fit it as a complete unit with the prod and spring assembled but it is more fiddly. If you want to do this, assemble the outer sleeve, inner sleeve and the spring and prod as a unit before insering into the cylinder. You then need to hold the prod and spring firmly in place as you wind the sleeve unit into the cylinder. It is possible with care.

When I first stripped a model 50, I had access to ‘Air Rifle and air piston maintenance and repair’ by Q Cobham ISBN-10 0-9553131-0-4 which gave me confidence to proceed. I supplemented my actions with more notes, upon which this account is based.

Cheers, Phil

[ggggr]

This is a slavia made break barrel pistol with a plastic body,a reasight adjustable for windage and a pivotting foresight adjustable for elevation. On the model I have, there is a knurled thing in the rear of the cylinder end cap, which unscrews and is actually a screwdriver for adjusting the trigger screw. remove this and keep it safe. The action is held in the body by a screw on either side of the body and a nut at the bottom of the pistol grip that may require a forked screwdriver to remove. Remove the two screws and nut and lift action from body( with luck the trigger spring should remain in the body) To remove barrel, undo lockscrew and barrel pivot screw. When you have done that you will need to knock out the front pin in the trigger housing otherwise you will not be able to remove barrel and cocking arm. With barrel out, you can remove pin holding barrel plunger in breech block and clean and lube and replace. There is no real need to remove trigger and sear although I think they would respond to a little polishing if you do. Before you attempt to unscrew cylinder end cap, remove the small pin on the underside of the cylinder that locates it (I used fingers but you may need a small screwdriver or long nose pliers) GO TO PART TWO

[ggggr]

You should now be able to unscew the end cap, using a large screwdriver at first and then your hand (remember to keep pressure on). When it unscrews, you can remove the guide, mainspring and piston. The piston head is a parachute washer which just seems to locate on a spiggot. The piston has slots on both sides but only one notch for the sear so make sure you put it back the right way round or the gun wont cock! The cocking arm slot would benefit from a bit of light,filing and polishing. Clean and lube. Replace piston (right way up), mainspring and guide and screw on endcap. I used a rigger glove to push down on the cap. Tighen the cap up but use a small screwdriver or pin to feel for the hole that the little pin locates in and then replace this when its lined up. Replace cocking arm in its slot and then replace the barrel and locate pivot screw and lock screw. Replace the pin at front of the trigger housing that keeps the cocking arm pushed down. Replace action in pistol body, making sure trigger spring does not come out and locates in the recess in sear. Replace two screws and the nut in the pistol grip.

[Garvin]

Paratrooper exploded view

Trigger detail

[Phil Russell]

Again maybe not quite a collectable but it is an old favourite and I note some forum members asking for advice at times. So here are some notes on the strip:

This guide gives instructions on how to strip the HW77 / 97 standard and Karbine versions. It does not contain information on tuning nor of stripping the Rekord trigger unit.

Tools required: 3mm punches (2), light hammer for punches, blade gunsmith screwdrivers to fit stock screws and trigger guard screws (no cross head screws), small adjustable spanner or spanner to fit the action retaining bolt..

Stripping:
Remove any telescopic sight and any rear sight.
Remove action from stock (2 x 5mm screws at the forend plus their retaining washers and 2 screws in the trigger guard). Remove trigger guard.
Lift action from stock.

Place action in a padded vice, barrel to the left and trigger uppermost.

Note the large threaded nut to the left of the trigger block. Undo and remove using the small adjustable spanner, taking care not to lose any spacing washers if they are loose. The anti-bear trap / safety slide is now free but held by the underlever.

Tap out the two pins that hold the trigger unit in place. I tap from front to back. The pins are of different lengths, a shorter top one near the end of the trigger block and a longer bottom one nearer the breech. Remove the trigger housing by tilting the trigger housing up and to the right. As you do this, keep a hand over the safety catch to prevent it pinging out. When the trigger unit is free, remove the safety slide plus its spring.

Remove the pin that holds the underlever in place on the breech and remove the underlever, raising it to disengage the end that goes into the compression cylinder slot. If you take care you need not knock the pin all the way out.
NOTE: if you are only replacing the spring and do not want to get at the compression cylinder and piston, you do not need to remove the underlever.

You now need to remove the end block that housed the trigger unit. The preload from the spring is not great but I advise wearing goggles and a glove on the hand you unscrew the block with.

Unscrew the block. It may be stiff to start, so you can place a lever in the trigger housing slot to start the movement. I use a piece of timber about 6” long. Take care as you unscrew the block, keeping watch on the screw threads. The block will suddenly lose the threads, so be prepared to support it with the gloved hand. Place the block on one side. The spring and spring guide can now be pulled out. If you removed the underlever, you can also now pull out the compression cylinder and piston assembly.

You can now service any parts you wish but at the least I recommend a clean of all parts and reassembly with fresh lubricant. I also fit a piston sleeve as a matter of course.
Next post: the rebuild
Cheers, Phil

[Phil Russell]

HW77 / 97 rebuild
Re-assembly:
This is basically a reversal of the above.
Begin by assembling the piston in the compression tube (remember suitable lubrication), making sure that the underlever slot in the piston lines up with the square hole in the compression tube. Fit this assembly into the action with the piston slot uppermost, in line with the underlever slot in the main action.

Refit the spring and spring guide, correctly lubricated, into the piston.

Now you need to refit the end block. With the block in your gloved hand, push against the end of the spring guide to bring the block up to the main cylinder. Turn the block to engage the threads. This is easiest done by pushing with the gloved hand and turning the block with the other. Screw the block into the action, taking care to look at the square hole in the cylinder and the slot in the piston to make sure they are not going out of alignment with the slot in the action. They can easily do so, but to stop or correct any movement I find it easy to hold a screwdriver in the slots to prevent the piston cylinder and piston tube from rotating. When you have screwed the end block in as far as you can by hand you may well need to apply some leverage to get it up tight. You can check this position by noting that the sides of the trigger housing slot line up with the action and the threaded bolt can be screwed into the block.

I now prefer to refit the underlever. Place the safety slide / antibear trap slide mechanism on top of the action and refit the underlever cocking arm end into the square hole and piston slot. Refit the underlever into the pivot at the end of the action and tap the pin home.

You can now secure the safety slide to the end of the action with the threaded bolt. Ensure the spacing washer is still in place. You need to push the safety slide a little against its spring pressure but it is easily done; refit the threaded bolt. Once fitted, just release the underlever and make sure the safety slide moves freely.

Now to refit the trigger. Refit the safety catch, remembering to put the spring on the catch before you push it through its locating hole in the end of the action. Hold the trigger unit with the left side slightly up and feed the trigger unit into the trigger housing, all the time keeping the safety catch pushed in against its spring. As you feed the trigger unit home, bottom right corner first, rotate the left edge down a little and it will fall easily into place. When the unit is seated, take two punches and place them through the holes in the action from the front to back, all the time holding the safety catch in. Then take the shorter pin and replace it through the action and trigger unit from the back towards the front. This will drive the punch out; the pin should go in quite easily. If it jams or refuses to go, do not force it; you will have the holes slightly out of alignment. Jiggle the punch to bring the holes into alignment.
Fit the long pin.

Make sure the captive nut at the top right of the trigger unit is in place ... a trigger guard screw fastens into this.

Refit action into the stock. Refit trigger guard. Job done. Refit sights and test rifle.
Cheers, Phil

[Jamie Norton]

Use a digital camera to take pics of the components (especially trigger assembly) BEFORE you dismantle them. Referring to the pics on reassembly could save you headaches

[Phil Russell]

Some notes on stripping and rebuilding the WEbley Victor and Vulcan Hopefully I have not forgotten anything. If so, just put me right or ask me.

WEBLEY VULCAN / VICTOR STRIP and REBUILD

The Webley Vulcan and Victor are basically the same rifle. The MK1 Vulcan had the same barrel length as the Victor (17.125”) but later Vulcan models had 19.25” barrels. The Vulcan has a safety catch and an adjustable trigger; the Victor does not. The Vulcan stock is longer than the Victor. Advertised power for the Victor was 720fps when new (pellet not specified).

These notes on striping and rebuilding the rifles do not include advice on tuning. Where they include reference to the safety catch or trigger adjustment, the notes apply to the Vulcan only; ignore them for the Victor.

Stripping:
Remove the stock: two screws in the forend and two screws in the trigger guard. I recommend removing both foresight and rear sight to prevent accidental damage. The rear sight can be removed as a complete assembly by undoing the two 4BA screws in the top.

To remove the spring and spring guide assembly: it is necessary to remove the trigger. This is not difficult but it pays to have a good look at the assembly before starting, or even take a photo to aid reassembly. It is only necessary to remove the actual trigger, not the complete trigger and sear assembly. To do this, remove the circlip and then the pin that acts as a pivot for the trigger and remove the trigger and a coiled trigger spring that fits into the end block.

To remove end block and spring assembly: Either hold the gun upright and press down on the end block while removing the pin that holds the end block to the action or use a spring compressor or vice to hold everything firm while the pin is removed. The preload is not excessive but is present nonetheless. With the end plug removed, the spring and spring guide can be removed.

To remove the piston assembly: it is necessary to remove the trigger sear and the cocking lever. To do this, remove the remaining two pins in the trigger assembly and remove the safety slide (for the Vulcan) and the sear and its spring (Vulcan and Victor). Be sure to note how the safety slide fits on the sear. Draw or photograph as appropriate.
To remove the cocking lever use a 5mm drift to remove the pin that holds the cocking lever to the breech. On some rifles it can be convenient to remove the complete barrel and cocking lever assembly by removing the pin or bolt that the breech pivots on. Unless you want to get at the barrel fixing / lock-up plunger, do not remove this pin on the Victor or Vulcan as if you do, the barrel plunger will be released. It is acted upon by a very firm spring and refitting it can be a bit awkward. By removing the pin from the cocking lever, the lever can be removed but leaves the barrel assembly in place. Once the lever is removed, the piston can be removed. The piston seal is in two parts, a seal and a cushion washer. Clean or replace as necessary. If the seal needs replacing, it is advised to cut the old seal away with a sharp knife, but the cushion washer simply lifts off.

Clean or replace parts as required.

Rebuilding:
Generally, rebuild is a reversal of the strip procedure.
A new cushion washer will slide on. To fit a new seal, place the seal against the retaining flange on the piston and press firmly with both thumbs until the seal clicks into place. A piston sleeve can be added if you wish. With the piston cleaned, lubricate as appropriate.

Lubricate the inner surface of the cylinder and refit the piston assembly, making sure the slot in the piston lines up with the slot in the cylinder. Refit the cocking lever into the cylinder/piston slot and refit the lever and its pivot pin in the breech.

The Webley Manual says to replace the trigger sear before replacing the spring and guide and end plug. In practice I have always replaced the spring, guide and end plug first.

Refit the spring and spring guide.
Refit the cylinder end plug and secure with its pin.

It is now time to refit the trigger.
Victor: I can do no better than give instructions from the Webley Manual: locate the sear spring onto the RH side of the sear with the cranked end through the small hole in the sear and its central hole aligned with the sear fulcrum pin hole. Feed this assembly into its correct position in the trigger housing, lining up the fulcrum hole in the sear with the relevant hole in the housing. Insert the fulcrum pin through the housing and sear from the left side and fit the circlip.
Vulcan: As above except that you need to position the safety slide on the sear as you feed it into position.
Fit the front fulcrum pin (nearest the barrel) making sure it passes through the forked end of the safety slide (Vulcan only).

Replace the trigger spring in the body end plug. Replace the trigger, holding the long leg of the sear spring out of the way towards the cylinder. Refit trigger pivot fulcrum pin and let the long leg of the sear spring rest against the fulcrum pin.

That should be job done. Refit the sights and reassemble into the stock. Test that the trigger sears engage and that the safety works. The safety can only be set (then unset) when the rifle is cocked. It is not set automatically on cocking.

Cheers, Phil

[david9d]

I have a copy of the handbook for the Osprey, which besides general advise has a good description of stripping and re-building. .
I have it available in PDF and in JPEG formats, but I don't know how to put it up on here.
Can anyone help please ?

David

[Phil Russell]

STRIP AND REBUILD AN EXCELLENT GEVARET PNEUMATIC RIFLE

The Excellent Gevaret rifles were made in Sweden from the early 1900s. This strip is for a model CII from around 1945. Ammunition is 5.4mm ball, which seems difficult to find but may be available in Sweden. The strip is based on my experiences in getting an auction buy working. When we got the rifle it would not cock and the pump, which is basically a bicycle pump, was not working.

Strip: Unscrew the pump cylinder complete with pump handle. Remove the single bolt that holds the stock to the action and remove the action. The trigger block and trigger simply unscrews complete with the exhaust valve and plunger. Collect any large shim washers that separate the trigger block from the sliding loading cover. The cover just slips off.
To access the inlet valve, simply unscrew the valve from where the pump cylinder screwed in. This reveals a valve consisting of a bicycle tyre valve. Ours was an old type with a bit of rubber tubing as the valve seal but I believe other types were sometimes fitted.
To strip the pump, remove the pump handle by undoing the screw on the handle top. Unscrew the top end of the pump cylinder and pull out the pump and rod / washer assembly ... just like a bicycle pump. Put the long spring to one side. Note that the pump washer is fitted to a brass plunger that can move in and out of the end of the rod. Note the two small holes in the rod where the washer assembly screws in and the small hole in the plunger in the centre of the washer. These holes allow air to enter the pump cylinder when the pump is withdrawn, but air is prevented from leaving the cylinder by a simple valve that is closed by air pressure when the pump is pushed down. To access this valve, simply unscrew the washer and plunger assembly from the rod .. there is a recess in the end of the pump rod and a rubber disc at its base.
The exhaust valve seal is clearly seen on the end of the plunger coming out of the trigger block.

Basically, that is it. You can strip the trigger block down if you wish. To check it is functioning, push the cocking plunger in and see if the sear engages. If it does, all is most likely OK, but if you wish to dismantle it then unscrew the cocking plunger cover to reveal the end of the valve rod. The trigger is retained by a simple spring and a pivot screw. The trigger has a sear cut into it. Unscrew the nut and remove the valve rod. Be prepared for two springs and a spacer. Clean and refit.

Rebuild: If needed, make and fit a new leather pump washer. Instructions on making leather washers are on the BBS. I replaced the small valve at the end of the pump rod with a disc of 3mm rubber sheet. I fitted a new exhaust valve seal, again from 3mm rubber sheet. Getting the latter thickness was a matter of trial and error. Too thin and the valve does not seal when the trigger is set, too thick and you cannot cock the trigger. The inlet valve rubber was replaced by a bit of silicon rubber tubing (1.5mm internal diameter) obtained from a fishing tackle shop where it is sold for fishermen to put on their floats.
Rebuild is a simple reversal of the strip. My first attempts failed due to air leaks in various places. I cured these by using plumbers ptfe tape around all threaded assemblies, including the thread on the cycle valve that acts as the inlet valve.
When screwing the trigger block back, remember that when mounted in the stock, the trigger block is in line with the action. The swinging loading port also needs to be a fair air seal against the barrel breech. The position of all these components is critical to getting the exhaust valve to seal and for air to transfer to the barrel. I needed to make an extra shim washer from a bit of beer can in order to get the exhaust valve to function properly and the loading port to seal effectively with the trigger block in the correct position. As I said ... trial and error solved it.

Cheers, Phil

[david9d]

Oh well, if it can't be put up on here directly I am willing to email a PDF copy to anyone who requests it through my email address - see my profile.
David

I have a copy of the handbook for the Osprey, which besides general advise has a good description of stripping and re-building. .
I have it available in PDF and in JPEG formats, but I don't know how to put it up on here.
Can anyone help please ?

David

[ggggr]

I got a dog rough one to play with so where Ive had to modify and improvise a bit. I stripped this right down because the stock was cracked and loose.
Undo and remove 2 screws on metal butt plate. Use a socket to undo the nut in the stock (a 9/16 AF fitted the one in mine) and the stock should slide off.Undo the cocking arm pivot screw and remove cocking arm. (on mine the thread was gone in the breech block so I tapped it to 5mm and made up a locknut out of round bar,which I cut a slot in and blued). Undo the locknut on the trigger adjusting screw and remove the screw. Remove the 2 trigger guard screws. You should be able to unhook the trigger spring now but mine was a bugger because of gunge. Unscrew the trigger pivot screw and remove trigger.Unscrew barrel pivot and remove barrel. You can remove small screw on side of breech if you need to get to plunger and its spring. On mine the cylinder end cap was tight so I had to get it into a vice to start to unscrew it from cylinder.Once unscrewed you should be able to remove mainspring and piston. (mine was so gunged the piston washer was stuck to the end of the cylinder. If the piston washer needs removing you will have to drill out the locking pin that holds the piston washer screw (look closely and you should see it).

[ggggr]

I made up a piston washer for this (and cursed sending one I had to someone a few months back). Everything is cleaned and lubed ready to go back together and assuming you have sorted the barrel plunger and spring and replaced it in breech. The breech washer was made up of very thin leather and soaked in almond oil and replaced. Fit piston washer to piston and replace in cylinder (someone on here suggested doing it dry and lubing after---I can see the point because of the difficulty getting past the threaded bit of the cylinder). Replace mainspring and cylinder end cap. Refit barrel and replace barrel pivot (I made up a locknut for this as well). Replace cocking arm and its pivot. Replace stock and nip up nut. Replace butt plate and 2 screws. Locate trigger spring and push trigger into housing and locate pivot screw. Replace trigger guard and then the trigger adjusting screw and locknut. If the gun wont cock becuase it feels as though the piston is hitting the trigger, you need to wind the screw in more. If it wont hold the piston then wind it out.
stripped another of these and had a problem with the barrel plunger/barrel lock up. The barrel was drooping a bit. If you take the barrel plunger out of the breech block and file the rear of the cut out, this usually lets the plunger come out a bit more and lifts the barrel up. On this one I noticed some movement on the cylinder and investigated. There is a non sprung plunger in the end of the cylinder. I removed this and put a filed down shake proof washer behind it as a shim. This cured the barrel droop.

[Phil Russell]

Here are some notes I made when curing a 766 that would not pump up. As far as I could see the pump seal was OK so I needed to delve a little deeper. My problem was the O ring on the valve body. I did not strip the valve itself.

CROSMAN 766 STRIP

Taking apart.
Remove barrel band (2 halves, single small screw goes though band)

Remove barrel band ends: plastic, lifts away.

Knock out the pin holding the pump lever to the pump tube.

Remove pump lever with pump attached.

Remove barrel: hex key on top of action.

With the breech block on its side, screws uppermost, stock to the right, remove the 4 screws. Keep top plate in position while doing this.

Gently prise the top plate off the bottom plate. Take care the pump handle plastic grip holder, black plastic sprung laden bit on left, does not ping out as you release the top plate. Top plate may come away with the trigger and safety catch or may leave trigger and safety in the bottom plate. Either way the trigger safety spring may become detached from its location on the safety. Do not worry. Remove trigger, spring and trigger pin.

Note position of trigger sear components.

Lift sear away, taking care not to lose the large spring that acts on the sear bar. Lift off the long spring and plastic peg that acts as the BB follower from its channel.

The valve housing is held by a screw to the left of the valve housing. Before releasing this, note the brass component at the top of the valve body towards the left. This has a small spring over it. Release and remove the screw holding the valve housing but hold the housing in position. Now gently lift the housing away to the right, catching the small spring on the brass piece and also noting that the striker piece and a black plastic end body will be released under spring pressure on the right hand side. Just go slowly and this component will not be forcibly ejected. The brass valve body will slide out of the air cylinder. If it is an easy, loose slide then inspect the O ring as it will most likely be worn.

If needed, replace O ring.

Clean all parts, especially the air cylinder.

I have not dismantled the valve.

Rebuilding
Reversal of above but these tricks may help.

Assemble valve body and housing into place in the air cylinder. Have the brass component in place but do not fit spring yet. Take care that the striker and its spring and the black plastic end cap are located correctly. Replace the screw to hold the valve housing.

Carefully replace the small spring over the brass component. There is just enough room to wiggle this over the component; it stays in place against the bottom plate.

Refit trigger sears in place and slip the sear spring into place.

Refit the pump handle retaining spring and catch ... take care it has a habit of falling out.

Refit the trigger and its rod with the safety spring under the trigger and the hooked end pointing up. At this stage I found it best to hook a small bit of thin wire over the long arm of the spring and feed it towards the trigger such that when the top plate is replaced it protrudes out of the trigger guard.

Replace top plate: a bit fiddly to do this and keep pump handle spring in place but persevere.

When located, pull on the bit of wire to pull the safety spring long leg downwards ... look through the hole for the safety catch to see if it has cleared the hole. When it has, feed the safety catch back into place and release the spring. Pull the bit of wire out.

Replace 4 plate screws.

Refit barrel, and pump etc.

Job done.