I just had a need to strip one of these to correct a couple of faults and was surprised we had not covered this classic yet. So here it is: really a very easy job but maybe daunting because the action looks complicated.
WEBLEY SERVICE MKII
This is a third series rifle, No. S9304 in .22 flavour. The strip was carried out in order to discover why the trigger was very light and to change the mainspring as power was a little down. The strip includes help on stripping the basic components to access the piston and mainspring,but does not deal with the front block with the barrel locking mechanism.
To begin the strip, remove the barrel. Remove the butt plate and then the stock by undoing the large screw bolt inside the end of the stock . The action is now a very handy size. With the trigger uppermost. undo the large bolt retaining screw at the front of the trigger housing and place it safe as it is easily lost. There is a thin screw that passes through the rear of the trigger guard/housing. Remove it but try and keep the trigger housing against the action; not crucial though. Now release the large bolt at the front and lift away the trigger housing complete with trigger and a long sear. Note the small spring in the sear. Do not remove it if it is firm but make sure you do not lose it. There is no need to remove the trigger or sear unless they need replacing.
Now to remove the cocking arm mechanism. It pivots on a pin, about 6mm diameter, at the front of the action. A small grub screw in the end of the action needs to be removed before you can drift this pin out. Put the grub screw safe and drift the pin out ... do not worry, it does not retain the mainspring. Remove the cocking linkage mechanism by unhooking it from the slot in the piston. There is no need to remove the interceptor sear (= anti-bear trap sear) on top of the action. This pops down to hold the piston back when the rifle is cocked and the barrel is ‘broken’. When the barrel is located against the action the barrel pushes the interceptor sear out of the way.
The mainspring and piston are held in by the threaded end block. To remove this I mounted the cylinder in a padded vice and carefully unscrewed the end block; starting the movement by using the flat side of a spanner. I realised that a small home-made tool would work wonders here ... a simple piece of wood 15mm x 18mm x about 10cm allowed me to unscrew the block easily. But I still wore a leather glove as I had no idea what preload was present. In fact, preload was not much and the end block had a captive spring guide so controlling the spring release was easy. The spring and end block simply lift away. The piston can be slid out but you need to depress the interceptor sear to allow the piston to pass it.
The spring was 32 coils at 3.1mm wire diameter. It was clear that the spring had seen better days as one end had severely compressed coils. A standard Airsporter spring was a perfect fit but on my spring was a coil too long so I trimmed it back to match the original.
The rebuild was basically a reverse of the strip. I removed and cleaned the piston; the piston ring was fine. As recommended, I relubed the ring with a little motor oil before refitting. Make sure the piston passes the interceptor sear. I now added the trigger housing. I realised that my light trigger issue had been due to the trigger housing not being bolted tight against the action. In part this was due to the location of the small locking screw because in its original position it allowed a little play in the main bolt. So I fitted a thin washer under the bolt head and the bolt now tightened nicely with the retaining screw perfectly aligned. The action was now again mounted in the padded vice. I lightly greased the spring before adding the end block and spring guide. There was about 20mm more preload with the new spring. I used my wooden tool in the end of the end block and compressed the spring and turned the tool to engage the threads. Not too difficult at all but I still wore a thick leather glove just in case it slipped. Screw the end block all the way in until the slots and the holes for the pivot pin align. Add the cocking linkage and feed the barrel pivot into the end block slot. Replace the pivot pin and add the retaining grub screw.
Replace stock and butt plate. Slide barrel back into its housing. Result: good trigger action again and increased performance at a little over 520fps. A couple of shots dieseled to begin with but the rifle soon settled down.
Tip: If you think the barrel is not seating properly, a new breech seal can be easily made from a red fibre washer. The barrel lock bolt handle pulls the barrel firmly against the breech seal.