DIANA MOD. 24 D (TO1 trigger) Part 2
Describing how to strip and rebuild the trigger unit is not very easy as there are several parts. A picture guide is available at The Dianawerk Collective. Search for ‘Diana48/52 TO1trigger disassembly/assembly’ and you will find it ... or just Google the search term. The plastic bits on the trigger unit are different but the working parts are the same.These following notes can be regarded as supplementary information. Looking at the trigger unit with the trigger blade pointing upwards and the barrel to the left, the bottom left pin holds the piston sear and its’ spring in place, the pin immediately above it is the trigger blade pivot pin and the pin on the right, half way up the housing, holds the trigger sear and its spring. The safety pivot pin is quite clear on the right top of the trigger unit and holds the safety spring as well. To get into the trigger unit, remove the safety catch pin and pull the safety catch back. It can be quite firm as you are releasing a sprung bar from one of the slave pins (if used). It comes away with the pronged legged spring. The trigger blade and coil spring comes away easily if you push its’ pin out. The trigger sear pin is next but take care as when the sear is released the small coil spring releases.. it should not ping into space but be prepared. The main piston sear pin is next to be removed along with its spring (another legged spring) and the sear itself.
I had no reason to take the three ball unit apart but if the mood strikes you, it is not too difficult. A few words about the basic construction will help. There is the housing body on the outside, the part that came out of the cylinder. On top of this is the long coiled spring fitted, easily visible. Note one end has a pin (like a small spring guide) inside the spring . The other end locates on a small prong on the outer shell, see below. Inside this outer housing is the inner cylinder that contains the 3 balls. Sandwiched between the outer housing and inner cylinder is a shorter ‘outer shell’ . You need to remove the long spring by inserting a small screwdriver into the housing and just levering the spring free at the pin end. Take care it does not ping away and keep a grip on the other components. Now note that there is a slot in line with the retaining pin holes and that there is another pin passing through the trigger housing in this slot. Push the pin out but keep hold of the shell and inner cylinder (with balls) within the housing so that they do not simply fall out everywhere. It’s not a real problem if they do, just easier to note how it all goes together if you hold them at this stage. With this pin removed you can slide out the inner cylinder and its’ outer shell. (The piston rod passes into the inner cylinder during cocking). The inner cylinder has the famous three balls. Balls are 4.8mm or 3/16” diameter, a common cycle bearing size. Note how the inner cylinder fits into the shorter outer shell and how these then slide into the outer housing. After cleaning, it is time to re-assemble the unit. Good fun. Begin by putting grease in each of the holes the balls fit into in the inner cylinder and put the balls in place. Slide the inner cylinder into the outer shell balls end first. The outer shell should have the prong that locates the end of the long spring in line with the long slot in the inner cylinder. Replace the inner cylinder and its’ shell into the trigger unit housing, making sure that the long slot in the inner cylinder lines up with the long slot in the outer housing. If this is not so, you have the inner cylinder upside down. Refit the pin that passes through the slot in the housing. Take the long coil spring, fit the pin in one end and insert the other end in the long slot in the outer housing such that the open end of the spring locates over the prong on the end of the outer shell. Holding all parts together, you now need to push on the pin in the end of this spring and slide it into the end of the long slot. The spring compresses maybe 6mm but it is not too difficult.
You can, if you wish now add the two slave pins again to hold all these bits together. The three ball section of the trigger is now almost done and all that remains is to re-assemble the trigger and its’ sears plus the safety catch.
First to be fitted is the piston sear and its spring ... the flat plate like sear that has 2 wings through which the locating pin passes. The spring fits inside these wings with its legs inside the arms of the plate and the central prong of the spring pointing up towards the trigger blade. The securing pin passes through the holes in the spring. Fitting is a bit fiddly but is not too bad: place the sear inside the trigger housing with the sear ‘dimple’ downwards and the spring roughly in place. Push against the sear and the spring, compressing the prong against the housing until you can fit the locating pin in place. You may find it easier to first locate a parallel punch and then tap it out with the pin. When fitted properly, the spring legs hold the sear plate firmly against the housing holding the balls etc.
Now for the trigger sear. Again a little fiddly but fine if you go carefully. The sear is fitted with its’ leg pointing downwards towards the ‘ball unit’ and the small prong on the sear pointing upwards towards the trigger blade. Once the retaining pin is in place, put the small coil spring over the prong and, slightly compressing the spring, slide the other end into the recess in the housing plate above. This then holds the trigger sear in place. The trigger can now be replaced ... put the trigger coil spring onto the peg on top of the trigger blade and locate the other end against the trigger housing. Slightly compress the trigger spring and replace the pin through the housing and the trigger blade. There is a groove in the trigger blade that slots over the trigger sear.
All that remains now is to replace the safety catch. Slide the safety catch bar into the inner cylinder. If you have slave pins fitted, make sure the bar fits over the nearest pin and that the sprung part of the bar fits over the pin. Fit the safety spring over the safety locating bracket with the pronged legs outwards and refit the retaining pin. The central tab on the spring tensions the spring against the housing. I found it easier to slip the pronged legs inside the safety catch plate while fitting the pin as it relieved some tension on the spring. Once the pin was in place I simply flipped the legs out again into place.
The unit is now rebuilt and ready for installation in the cylinder.
To re-assemble the rifle, put the piston in the cylinder, lubricated as necessary and taking care not to catch the piston seal on any edges of slots in the cylinder. Add the lightly greased spring and guide. Place cylinder in spring compressor and add the trigger housing unit. Add the small spacer block to clear the safety catch and compress the unit until the retaining pin holes in the trigger housing line up with the holes in the cylinder. If you have used slave pins then simply drive them out using the proper retaining pins. If you have not used slave pins you will find it easier to use a parallel punch first and then push the punch out using the pins. Note that the safety catch bar needs to be out, in the safe position, and the bar depressed using a small screwdriver to allow the pin to pass through the housing ... if you look into the housing you can see the bar just blocking free passage of the pin.
Add the barrel and breech assembly and the cocking lever. If you need a new breech seal it is a BS109, often fitted with a small shim underneath. Replace the plastic end cap and refit action into the stock. Add the sights and test. Job done. I believe the rifle usually ran at c. 700 fps. Mine was running at c. 550 – 640 fps depending on pellet so I suspect my mainspring is a little tired. I will replace it in due course.
Cheers, Phil