Different size cylinders and power.

[robs5230]

The piston seal was in the gun (obviously) so not sure how old it is, I did try fitting a new one but buggered up the dovetail part fixing lug because I didn't use the magic Theoben way of fitting it , I used a Titan no14 spring which I had to shorten by 3 coils as it was impossible trying to get it in the cylinder without doing myself an injury or risk having it torpedo around the shed, I used the usual .177 AA domed pellets, the spring guide is a snug fit, not tight that you have to really push it hard to get it on.

Like I said before I didn't really give it that much time as the circlip that holds the rear guide in looks a bit worn and I didn't want to risk breaking it as with most Theoben parts now they are either hard to get or bloody expensive, I could have tried some preload washers and that may have got the power up into the 10ftp area but like you say, I think the seal may need replacing but I don't really want to spend another £30 at the moment on another seal when my next project is waiting to be worked on (infact I've just bought some stuff for it today).

Pete

Not familiar with the titan 14 in terms of sizing but it looks like a diana 350 replacement.
Just seen in your signature a scirocco in .177. Was that the rifle you tried springing? Mine was .22

[look no hands]

Not familiar with the titan 14 in terms of sizing but it looks like a diana 350 replacement.
Just seen in your signature a scirocco in .177. Was that the rifle you tried springing? Mine was .22

Yep, my Sirocco's a .177 HE, the Titan no14 is a beast of a spring, you're right it is for a Diana 350 and a Webley Patriot.

Pete

[robs5230]

Yep, my Sirocco's a .177 HE, the Titan no14 is a beast of a spring, you're right it is for a Diana 350 and a Webley Patriot.

Pete

mmm.. Like I said I'd have used an 80 type spring but mine definitely made more power, maybe the calibre helped.
What's the spec on that no14 ? wire thickness, i.d., o.d. ?

[look no hands]

mmm.. Like I said I'd have used an 80 type spring but mine definitely made more power, maybe the calibre helped.
What's the spec on that no14 ? wire thickness, i.d., o.d. ?

No. 14

OD 22.7

ID 15.4

Wire 3.60

Coils 37

Length 358

Pete

[robs5230]

No. 14

OD 22.7

ID 15.4

Wire 3.60

Coils 37

Length 358

Pete

Thats 7 coils and around 60mm longer than an 80 spring. If that were me , I'd start chopping coils till there was power loss. I'd think you'd get gain before loss.

[look no hands]

Thats 7 coils and around 60mm longer than an 80 spring. If that were me , I'd start chopping coils till there was power loss. I'd think you'd get gain before loss.

The spring has been reduced to 34 coils to be able to get it in the cylinder as my spring compressor didn't have enough travel to get the whole spring in.

So you recon if I took even more coils off, I'd gain power?

Pete

[robs5230]

The spring has been reduced to 34 coils to be able to get it in the cylinder as my spring compressor didn't have enough travel to get the whole spring in.

So you recon if I took even more coils off, I'd gain power?

Pete

It was mentioned earlier that it may be over sprung. You're fighting a heavy piston, a crap seal and a less inefficient calibre but other than time and effort you've little to lose here Pete.
The way I go with springs is multiple small cuts and refinishes and cut until power does drop off. I accept on normal springers, I'm working within known parameters, but I'm sure that spring has more to give in that scirrocco.

[Barryg]

Pete, just wondering if you had seen this

https://www.trrobb.com/Theoben_Gas_r...8_9923664.aspx

[robs5230]

Pete, just wondering if you had seen this

https://www.trrobb.com/Theoben_Gas_r...8_9923664.aspx

That does look like it has the other type of dummy piston, but I can only imagine the spring would work.

[look no hands]

Pete, just wondering if you had seen this

https://www.trrobb.com/Theoben_Gas_r...8_9923664.aspx

I did see it Barry, thanks for showing me anyway, that kit is for the earlier models held in with a pin, I did see it said he can supply for the other models but I wanted to see what I could do it first without spending £70.

Pete

[look no hands]

It was mentioned earlier that it may be over sprung. You're fighting a heavy piston, a crap seal and a less inefficient calibre but other than time and effort you've little to lose here Pete.
The way I go with springs is multiple small cuts and refinishes and cut until power does drop off. I accept on normal springers, I'm working within known parameters, but I'm sure that spring has more to give in that scirrocco.

I may take another coil off then and see what happens, at least it should be easier getting in if it is shorter

I wonder if it's worth trying to make an adapter (or even a complete new piston which has been lightened) to fit a different type seal as custom seals of Oz make THIS which may seal better than the Theoben one?

Pete

[robs5230]

I may take another coil off then and see what happens, at least it should be easier getting in if it is shorter

I wonder if it's worth trying to make an adapter (or even a complete new piston which has been lightened) to fit a different type seal as custom seals of Oz make THIS which may seal better than the Theoben one?

Pete

Its all got to be worth a try. A cheaper way would be O ring for the piston seal. Maybe even a groove cut in the piston behind the standard seal would be ok and possibly some sort of bearing or o ring at the rear of the piston to stabilise it. I can't remember the exact design of the outer piston from memory but with the ram complete, its centralised by the rod of the dummy piston.

I'm still on the lookout for a fenman to do the same thing with and when I find one, I won't be beat

[Hsing-ee]

I had one rifle that increased dramatically in power with a weaker spring... I think the heavy spring meant the piston bounce was knackering the whole cycle. Good luck with the despringing ...

[look no hands]

I had one rifle that increased dramatically in power with a weaker spring... I think the heavy spring meant the piston bounce was knackering the whole cycle. Good luck with the despringing ...

I may have a go tomorrow, I've only managed to strip the Airsporter RB2 this afternoon and see if a particular tuning kit fits it, which hopefully it should with a slight adjustment, if it works and is nice to shoot then it will be an interesting conversion

Pete

[Rickenbacker]

I've never experienced the oversprung phenomenon meself.

Less spring has always lowered the power, but I suppose I've never tried using that much too much spring.