AirGunTech: Re Engineering Spring Powered Air Rifles for smoothness, consistency, and to better suit UK power levels.

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.

 

 

 

 

 

  • This gun is so so sweet to shoot – thanks for giving me the chance to try it out.

  • Glad you like is Steve…its for sure an eye opener and considering the guns can be picked up for £300 or so with the added cost of the sleeve and the LGV piston for anyone with access to a lathe it still makes the guns attractive as it shoots way better than a stock TX200.

    Now to find how to rebarrel one down to .177 ;)

  • I am restoring a rough D52 T01 in 177, so this is fascinating to me as this damn thing seems hard wired to put out 15ft/lb no matter how feebly I spring it

  • I feel your pain there, I have a dog rough. 22 T01, it was producing 15 ft/lbs with the stock, never changed main spring….despite it being broken
    Quite a conundrum to restore, hard to know quite what to put in it, a biro spring?

  • I am very interested in your Model 54 buildup. I am a machinist and airgunner in USA and I am trying to build up an Air king for WFTF competition. I would love to chat with you about your piston setup I am machining my own and going with an 0-ring seal on it. Also going to destroke the FAC rifle to attain the 12ftlbs. Any information you could provide would be most helpful. Thanks for sharing this with others. Peace

    Pete

  • Pete

    You REALLY want to do a 25mm conversion on the piston and sleeve the comp tube down, set stroke to 75mm, set piston weight to 230g with tophat, lighter if you can but do not go below 200g. Use the HW 25mm seal, or size down a new style 25mm HW seal…or use a VAC 25 BUT watch its OD some have been small. Use the 16J UK spec spring with a new guide and tophat.

    I was able to push back the travel on my 54 sled to just 9mm, the gun uses around 7mm of this. I did this by making a travel reducer that sits up front on the front sled and this also pushed the trigger back for me to make the LOP a little nicer. Overall it made my 54 into an utter tack driver out to 50yards+ and much like a PCP to shoot.You may also want to make up new breech seals from something like nylotron with and incorporated O ring so you can reduce the TP dia down, stock they are 4mm, this may be ok BUT I have a feeling 3mm would be nicer.

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