Revisiting the Diana 52 Carbine
Event though I had the D52 shooting quite nice, i knew it could be better…with the Walther LGV piston being such a universal base for conversions I decided to see if it could get it to fit in the D52 and by making up a new longer piston rod reduce the stroke…and of course sleeve the compression tube down to 25mm
First job was the sleeve the compression tube, did not get any pics of this as we all know what a piece of steel tube looks like machined square on both ends and cleaned/polish. The tube used is 28mm OD 1.5mm wall high precision hydraulic steel tube, machined square and true both ends, the comp tube open end is relieved a little so the piston is easy to insert, the end that sits on the breech is as flat and true as I could get it…the tube is pressed home and secured with loctite thread lock. Cut this sleeve +2mm length, measure the internal length of the compression tube and just add 2mm, it will clear the skirt on the piston by around 4mm
Now..the D52 has a central transfer port, this means the Walther Piston seal can NOT be used for this conversion, I opted for the Vortek Vac25 seal (although a second hand one showing some signs of wear..will get changed when the next order comes in). If you are considering this conversion then you really do need to consider the added cost of a replacement seal as well as buying the LGV piston.
Next job is removing the rear bearing on the piston and machining a new one. The ID is the diameter of the groove cut into the piston, for me this was 27.20mm, the OD is 31mm, the width is around 4mm but measure the groove as you machine a new bearing to suit. So you are replacing a 30mm OD bearing with a 31mm OD bearing
Once done you have to remove the OEM rod from the piston, I held the rod in the lathe and heated the nose of the piston till it started smoking then using some grips wind the piston off the rod..they are loctited on. The thread is M8x1mm so if you want to clean out the threads in the piston nose you are going to need an M8x1mm tap. Next reproduce what is on the end of the OEM piston rod onto a nice fresh piece of 10mm OD silver steel bar that is precut to 210mm long for .22 (205mm for .177)
The rods total length is 210mm, the sear engagement point lands at 207mm for .22 and will be at 202mm for .177.
This is the piston nose end, top OEM bottom the one I machined..it was identical but i had to lengthen stroke by 3mm hence the thread on the bottom self machined piece is shorter.
As you see what you end up with is quite a bit longer, remember this rod here is for a 70mm stroke for a .22 D52 to UK spec.
Here is the trigger sear end, copy exactly what is on the Diana piston remember…NOT the walther piston .
Remember you have to harden this after polishing.
All built up with fresh loctite on the threads you should end up with something like this.
Now, the spring to use is the full length spring you get with the D52 Ultra K here in the UK which pretty much is the full FAC spring, I used the OEM rear guide but shortened it by 10mm (off its nose) so I could install a top hat. This top hat has 3mm step on the end and I added an additional 3mm of preload, total preload on the spring is approx 45mm. Diana deliver the guns dry internally, make sure to grease the spring up and the guides, the piston seal just needs a tiny smear of moly lube or SM50 with the same on the front nose bearing on the piston..on the rear bearing i used high moly content grease.
So thats about it, rebuilt the rifle and just started tests, its touching 11fpe with 14.5gr RWS Superdomes. I expect it will gain 0.1 to 0.3fpe as it shoots in. The shot cycle is nothing short of amazing, 70mm stroke on this 258gramm piston in such a large gun means it bearly recoils…silky smooth to shoot.
I will update once I shoot the rifle at the local club over the coming week. I have to say it feels NOTHING like a stock Diana 52 to shoot, it feels much like a heavily tune HW77 mk1, for me for UK use this has to be the ultimate tune for the D52.