Idiots guide to classic airgun strips (pt 1)

[Phil Russell]

DIANA MOD. 24 D (TO1 trigger) Part 1

I bought this at auction for £20. It looked awful; the action was somewhat pitted and rusty, the rear sight was broken and the rifle would not cock. In its favour, the cocking action was quite smooth and the stock was pretty good. My main purpose in buying it was to see if I could copy the safety catch as I have a Webley Air Wolf that is deemed to be a rebadged Diana 24. I was thwarted in this objective as when I started to clean the action, the magic marks 24 with a letter D beneath were revealed. This was thus a Mod. 24D and not the Air Wolf version which was, I believe a simple Mod. 24. Nevertheless, I continued, reasonably confident that I could restore the rifle to working condition. A few surprises awaited me ...
The stock is easily released by removing the two screws in the forend and the front bolt in the trigger guard. The rear bolt is a wood screw. The action just lifts out. When I did this, two of the trigger pins that secure the sears fell out. They are longer than the trigger housing and are held in place (seemingly) by being the same width as the cut out in the stock ... so when the action is in the stock the pins cannot move. But they were quite a loose fit in the trigger block: be warned. I replaced them and put small strips of masking tape over the ends to keep them in place.
Once out of the stock it was clear that the trigger unit was a Diana TO1 and is assembled in a housing that can be removed from the action without taking the trigger apart ... memories of the Original 48/52 flooded back as some models had the same trigger unit.
The first job was to remove the trigger housing. I recommend the use of a spring compressor and two slave pins, each 24mm x 5mm diameter. The plastic end cap simply pulls off the rear of the cylinder. Put action in a spring compressor, trigger uppermost and to the right. Depending on the clearances you have with the compressor, I recommend removing front and rear sight units. As the safety catch extends beyond the end of the cylinder you need a small wooden block to butt up against the end of the cylinder and trigger housing as you take the strain of the two pins that you can see going through the cylinder and the trigger housing ... the two pins to the extreme right of the action. This is where the two slave pins are very useful. Use the slave pins to drift out the pins holding the trigger housing to the cylinder. The slave pins are just long enough to maintain the trigger unit in a working state when out of the action, but short enough to allow the trigger housing to slide in the cylinder. With both slave pins in place, release pressure on the trigger housing and let the mainspring come free. On my rifle there was about two inches of preload; the trigger housing coming almost free from the cylinder. Of course, you could achieve the same effect by not using the slave pins and simply drifting the pins out using a parallel punch. If you do this you will release the safety bar from its place as you remove the punch. This is not critical, but using slave pins is easier.
Once the trigger housing is out you can remove the mainspring and spring guide. I was surprised to see that my guide was delrin leading me to think that it was an aftermarket one. To release the piston, you need to release the cocking link; a simple pin through the breech but note that it is retained by a circlip between the arms of the link that will need removing first. This is a bit fiddly and I know of at least one rifle where the circlip is missing. I removed the barrel assembly as well; a bolt that passes through a steel sleeve that passes through the breech jaws and the breech. With the cocking link removed, the piston simply slides out. Again I was quite surprised; a long, heavy piston greeted me, complete with a synthetic piston head. It looked quite good.
I now started to wonder why the rifle would not cock. The spring seemed OK and there was nothing obvious to impede the cocking stroke. To check trigger action I took the piston and pushed it firmly into the end of the trigger housing. Nothing happened. The piston did not lock in place. Note that if you used a punch to remove the pins earlier then the trigger will not engage with the sear mechanism until the pins are replaced in the trigger housing and the safety activated. (Not actually 100% true as if the safety slide is removed, the trigger will cock; but it still needs the pins in place). So I had a trigger problem.
This was my first experience of stripping the TO1 trigger even though I have stripped and rebuilt several three ball triggers from the Original 50 / 35 series and removed the TO1 unit from Original 48/52 rifles. Inspecting the trigger unit and comparing observations with the exploded diagram provided by Chambers, it was clear where my problem lay. The trigger unit has five springs: one is very clear, a strong coil spring about 4cm long sitting in a groove on top of the trigger housing, a large open coil spring that connects the plastic trigger blade to the trigger housing, a smaller diameter (about 3mm and 1cm long) coil spring that sits underneath the trigger sear bar, a spring with two legs that holds the piston sear down and finally another ‘legged’ spring that holds the safety catch in engagement. My trigger was missing these final three springs.

Cheers, Phil.
Continued in Part 2