Comp tube....

[rhyslightnin]

Ok.. so as soon as my new seal arrives I'm going to pull my 77 apart again!! Yay! I have to say I'm really looking forward to it. When I pulled it apart last time I noticed that the piston and stroke loosened towards the end of the compression tube as I pushed the piston into it by hand and I wondered if this ment the tube was not quite the right shape (ie bigger at the end of the compression). I wanted to fit a new seal anyway because for me I want the shot cycle to be more of a "plonk" rather than a "clack" & I think a tighter seal would give me that So my question is without polishing out the honing on the inside or re honing it after what is the best way to make sure the comp tube is nice and straight from start to finish?
Thanks all
Rhys

[TonyL]

Mmm....if it does feel like it might not be uniform for the length of the compression stroke, I'd say a precision machining shop would be the best port of call, Rhys.

Maybe NickG could do something? I think he could also actually make a comp tube from scratch, maybe? And, if so, to reduce the cost, I wonder if he would do an exchange on your current comp tube, as he could most likely use that as a basis for a narrow bore conversion for another project?

[rhyslightnin]

Mmm....if it does feel like it might not be uniform for the length of the compression stroke, I'd say a precision machining shop would be the best port of call, Rhys.

Maybe NickG could do something? I think he could also actually make a comp tube from scratch, maybe? And, if so, to reduce the cost, I wonder if he would do an exchange on your current comp tube, as he could most likely use that as a basis for a narrow bore conversion for another project?

Blimey ok... I was thinking along the lines of a bit of a polish with a broom handle & some p600 & pop a new seal in!!!! Lol... I didn't think it would be massively critical as I don't recall it being really noticeable but I did notice something if you know what I mean. Anyway I'll soon know when I pull it apart again .
If it's got to go to a machine shop then I may as well just buy a 25mm conversation or something...
Thanks Tone

Rhys

[Shed tuner]

Indeed, if it really is larger at the compression end, it can't be fixed - buy a 25mm one. Or sleave it to 22mm.

However choosing a slightly tighter seal with a nice flexible lip will probably compensate for it, and give you a calmer shot cycle.

PS make sure what you are feeling is not just down to lube and a smoother finish in the stroke part of the tube.

[rhyslightnin]

Indeed, if it really is larger at the compression end, it can't be fixed - buy a 25mm one. Or sleave it to 22mm.

However choosing a slightly tighter seal with a nice flexible lip will probably compensate for it, and give you a calmer shot cycle.

PS make sure what you are feeling is not just down to lube and a smoother finish in the stroke part of the tube.

OK.. Thanks Jon That sounds promising.. Just A few questions then please...
So how far into the compression tube will the piston sit normally just prior to the shot cycle?
Should I skip sizing the seal if the comp tube is a bit wonkey?
How can I tell if the tube is actually wonkey and its not just lube & finish?

Thanks sir!!
Rhys

[TonyL]

The stroke is 81mm, Rhys.

Rather than getting too hung up on this just yet, maybe just go for a slightly more snug fitting seal as Jon suggests, let it all run in and see how she goes?

[rhyslightnin]

The stroke is 81mm, Rhys.

Rather than getting too hung up on this just yet, maybe just go for a slightly more snug fitting seal as Jon suggests, let it all run in and see how she goes?

That is what I will do regardless Tone yes, I'll not be sweating it until I've tried that & even if it is a problem but it shoots well I may not be bothered to do anything about it anyway... Its just the inquisitive me that wishes to suck up the info and want to learn all this stuff

So 81mm from the end (transfer port end) outward?

Thanks Tone
Rhys

[TonyL]

That is what I will do regardless Tone yes, I'll not be sweating it until I've tried that & even if it is a problem but it shoots well I may not be bothered to do anything about it anyway... Its just the inquisitive me that wishes to suck up the info and want to learn all this stuff

So 81mm from the end (transfer port end) outward?

Thanks Tone
Rhys

Yep, 81mm from the TP end is the "swept area" matey.

And nothing wrong with being inquisitive.

There are lots of things that I know about our lovely boingers that I haven't put into practice. Some may happen one day, others maybe not. And due to lack of time, proper workshop, equipment etc. And fear of buggering up a perfectly good gun if it goes wrong! But that'll be where some cheapy nasties come into their own!

[BTDT]

I did some tests compressing HW seals to the equivalent psi start pressures of a couple of pellets, and they expanded in diameter.

At the start pressure of 7.3gn JSB pellets (just 120 psi), the seal diameter increased by 0.46mm and, at the start pressure of 8.7gn JSB pellets (150 psi). that increased to 0.47mm. The further the seal travels, the wider it gets.

I'd try the compression tube before writing it off. It'll quite possibly be fine.

[rhyslightnin]

I did some tests compressing HW seals to the equivalent psi start pressures of a couple of pellets, and they expanded in diameter.

At the start pressure of 7.3gn JSB pellets (just 120 psi), the seal diameter increased by 0.46mm and, at the start pressure of 8.7gn JSB pellets (150 psi). that increased to 0.47mm. The further the seal travels, the wider it gets.

I'd try the compression tube before writing it off. It'll quite possibly be fine.

Thanks Jim, to be honest it probably is just me being over inquisitive, as it was the first time I've ever pulled a springer apart and I was at the bash in a field, not the best environment so I'm not dead cirtan I'm not just getting myself at it!! So its nice to hear what people have to say before I delve in again.
Interesting info though as was the article in agw on piston extentions Thanks!.. I've got a couple of those to play with also which is going to be fun!

Thanks for the info!
Rhys