The Lesser Spotted Original/Diana 35

[T 20]

I thought it would be a good idea to keep you good folks updated on progress.

I've machined a 100mm long properly fitting Spring guide from 316 stainless and polished it up so that job's done.

I've cut and fitted a 0.25mm piston sleeve and slip washer to the piston which has brought it's weight upto 249 grams.

I'm aiming to end up at about 270 - 280 grams and I'll now be going for a slightly heavier piston nose and just a 1mm stroke increase for a good reason.
I'll be using a BSA Mercury sized O ring with a 3.175mm cross section for the piston seal and I'd like to keep 2mm of piston head either side of it so I'll end up with a 7.175mm wide piston head --- say 7.5 allowing for groove clearance.
The leather piston head was 8.5mm wide so at 7.5mm wide for the new O ring piston head I'll be gaining just 1mm of stroke taking it upto a 70mm stroke.
I've calculated that the new piston head will weigh in at 25grams compared to the leather sealed piston head's weight of 6grams so fitting this will take the overall piston weight upto 268grams (249+19).


As a bit of bonus good news, I originally wrote on this thread that the transfer port was 26mm long as that is what someone had posted on here --- this isn't true.
My LG35 has an overall transfer port length to the cylinder of 19.2mm with 17mm of that length at 4mm ID the other 2.2mm is a little domed collection chamber in the centre of the cylinder.
I can only assume the chap who measured the transfer port at 26mm had his vernier slip into the Allen key hole in the front of the piston when he measured it ?

So now I'm aiming at :-

A swept volume of 43.12cc (28mm bore X 70mm stroke)

A transfer port volume of 0.105cc (sleeved down to 2.8mm X 17mm)

A static compression ratio of about 410:1 --- I can't work this out exactly due to not knowing the collection chamber volume.

And an all up piston weight so about 275grams --- I'm allowing some for a Delrin top hat.





All the best Mick

[Geezer]

Very interesting, Mick.

This thread is also a handy reminder that until the US “adult airgun” thing of the early 70s started by Bob Law and then Bob Beeman, and taken up a few years later by AGW, the efficiency and power of springers was largely guesswork, including for the makers. Because:

1. No-one had access to chronos.
2. If it worked, no-one cared about the maths or the design.
3. Why spend cash doing the maths/physics?
4. Airguns were airguns, not military sniper rifles, so who cared?
5. Existing designs in production. Just keep making them. And they sell.

The realisation that long-stroke was a better way of making power than cylinder bore size began (a bit) with the FWB Sport in 1972, but only really hit home with the HW80 compared to the HW35. The Diana 35, compared to the 27 which comes fairly close in power, tried to have higher power primarily by increasing the bore, not the stroke.

[TonyL]

Super information as always, Mick.

Hoping the 'O' ring, that small stroke gain and heavier piston nose works well.

Have you settled on a spring spec?

[T 20]

Super information as always, Mick.

Hoping the 'O' ring, that small stroke gain and heavier piston nose works well.

Have you settled on a spring spec?

I'm turning it into a long stroked BSA Mercury, Tone --- what could possible go wrong ?

The increase in stroke by just 1mm is in aid of keeping the overal piston weight down yet keeping the O ring retained by a 2mm wall either side of it --- the 2mm bronze walls also act as a bearing surfaces.

I'm trying to keep the overall piston weight down to around 270grams then I can possibly add another 30grams by way of a top hat come piston weight if needed --- Mercury Pistons weigh about 300grams.

I'm carrying on with the 28 coil HW95 Spring for now as I have a few of those and I also have some new Titans and Airforce springs with the same ID.

The Original LG35 Spring from the factory was 33 coils, the Airsporter and Mercury factory springs were 29 coils, I'm happy to continue using the 28 coil Weihrach Spring for now as it was giving a consistent 11.2ftlbs with the leather seal --- let's see what it does with an Oring with a higher SCR.

I'm still a few days away from finding out if this all works as the compression tube needs a lot of time spending on it before I stuff an O ring up its chuff.




All the best Mick

[T 20]

image.jpg


It's all glued together with Gorilla snot now and curing.

While I had the O ring on I managed to slide it into the cylinder and try it --- all good, TFFT.

I found that I had to give the front face of the piston a light tickle with the lathe to flatten the front face but I'm still cock on at just a 1mm stroke increase.

[HW777]

image.jpg


It's all glued together with Gorilla snot now and curing.

While I had the O ring on I managed to slide it into the cylinder and try it --- all good, TFFT.

I found that I had to give the front face of the piston a light tickle with the lathe to flatten the front face but I'm still cock on at just a 1mm stroke increase.

Had all this work to the D35 been available back when this model was first sold, I wonder if Diana would have taken note ?

It is looking like you will have a supreme D35 in shooting characteristics Mick

But she's still a minger in the looks department

Atb

John

[TonyL]

image.jpg


It's all glued together with Gorilla snot now and curing.

While I had the O ring on I managed to slide it into the cylinder and try it --- all good, TFFT.

I found that I had to give the front face of the piston a light tickle with the lathe to flatten the front face but I'm still cock on at just a 1mm stroke increase.

Looking good, Michael.

[TonyL]

Had all this work to the D35 been available back when this model was first sold, I wonder if Diana would have taken note ?

John

Doubtful, John.

[T 20]

After a couple of machining cock ups the transfer port is now sleeved down from 4mm to 2.8mm. :-

image.jpg


I machined the first one a gnat's cock too small and then bugger me I machined the second one half a gnat's too small.
Rather than mess about machining a third one I simply tinned the second one with solder and glued it in with Loctite, with it tinned I had to knock it in with a hammer and punch and then open the ID back up to 2.8mm.

I'm working on the cylinder now, I've filed the cocking slot and all the other slots and holes so that an O ring piston head will slide past them without taking chunks out of it.
I've also had a bit of 360 grit paper on a stick and have taken down the spot welds for the scope rail and generally tidied up the inside of the tube, the bit that's been the biggest pain is these. :-

image.jpg

The stampings for the "Original" and "Model 35" have distorted the tube on the inside so I've had to sand these down inside as well as being carefull not to sand in the compression chamber section.

With an 1 1/8" O ring fitted to the piston it was a bit too tight in the compression chamber but rather than chucking the piston up in the lathe to deepen the O ring groove to reduce the crush I simply put a 1" O ring on the head --- perfect.

Next up will be polishing the cylinder with Solvo Autosol Chrome polish, then I'll be burnishing dry Moly into the cylinder walls, then hopefully I can assemble the action.

I also need to check the barrel for straightness and correct it if necessary before complete assembly.



All the best Mick

[Shed tuner]

let's have a bet on power output.

I'm guesing a tad warm and a hurried strippdown / coil chop.

[T 20]

let's have a bet on power output.

I'm guesing a tad warm and a hurried strippdown / coil chop.

You could well be right, Jon, but that would be of interest to those with .177" Original 35s.

Everything is prepared now ready for the big build and looking very sexy if I say so myself.
The piston ended up at 276 grams once I'd added a Delrin top hat.
The barrel was only slightly bent upwards but it's dead straight now.
As I had 16mm of preload with the leather sealed piston I've kept that the same for the build up with an O ring seal, having 6mm of top hat/slip washer in the piston and a 10mm stack of Dowty washers on the spring guide.
If it does go over I can simply remove preload from the back end and not disturb the piston which will give me a better idea of what it's doing.
If I feel it needs more piston weight I can simply pull the top hat out and I have some 10mm washers that weigh 4 grams each I can load the piston with, but I can only physically get four in.

If I get some numbers tomorrow I'll post them, but then I'll have to make a spring compressor before carrying on with the fine tuning.




All the best Mick

[Shed tuner]

I reckon the piston will be plenty heavy enough now you have gone for an o-ring setup Mick...

[evert]

Is there any chance the Diana 35 might suffer from the infamous porous breech syndrome??

[T 20]

I reckon the piston will be plenty heavy enough now you have gone for an o-ring setup Mick...

Yes Jon,
I'm 12 grams over the weight of a synthetic sealed HW35 piston and about 26 grams lower in weight than a Mercury piston, which is why I went for a conservative 2.8mm transfer port.
I've got a feeling that my O ringed HW35 has about a 270 gram piston with 71mm stroke and 2.8mm transfer port so I'm hoping to be in about the right ballpark with this one.


All the best Mick

[T 20]

Is there any chance the Diana 35 might suffer from the infamous porous breech syndrome??

There's every chance of that, evert.

I'm sure that I have an Airsporter MK4 action that has a porous breech, I never bothered investigating it as I used the stock off it on a MK2 --- which is a much better gun.

I watched an Indian YouTube video last night where a Diana 38 had blown the breech block out of the cylinder which is a bit worrying. :-

https://m.youtube.com/watch?v=0pvEoCENlU0



All the best Mick