Sizing seals in springers

[Shed tuner]

sounds good.. Resist any temptation to do any more piston sizing; just shoot 2 or 3 dozen, then rough tune the spring spacing... it'll probably wear in and creep up a bit more, but most of the wear will come very quickly. Certainly by the time you have shot 1/2 a tin, it'll be completely settled / worn in .

Are you using the original MK3 spring still ? And have you kept the large and excessively heavy steel piston weight / top hat (you can see where this is going) ?

[hmangphilly]

What sort of variance did you find? Given the number of successful TX on the competition circuit I can only surmise that a slight (undefined) variation in dimension is of no importance ... presumably once the seal has 'bedded in'. Surely AA work to a tolerance level and as long as the cylinder is within tolerance then performance is assured. But what is the tolerance? I ask out of sheer ignorance as I have no equipment capable of measuring the variability in id of cylinders. Are we talking about 1 or 2 thou? ... or is that a pipe dream (no pun intended).
Cheers, Phil

Oh Phil it was ages ago

If I remember the worst one was about 0.3 or 0.4 out of round and tapered .

As Jon says the abt grooves are smashed in there . The cocking flat too , but it’s far enough up at the end Ti not be a big problem .

Sure lots of them Shoot Just fine despite all this . And stupid tight seals

Goes to show how a para seal will cover up all sorts of errors

Don’t make it right though .

[Hsing-ee]

Use a leather washer if you are worried about out of true, just soak in neatfoot oil overnight, then squeeze out excess and take to the range to shoot it in. It should only take about 20 or 30 tins of pellets.

[Shed tuner]

Use a leather washer if you are worried about out of true, just soak in neatfoot oil overnight, then squeeze out excess and take to the range to shoot it in. It should only take about 20 or 30 tins of pellets.

damn, he's breached the wall...

[Vernal]

[QUOTE=Shed

Are you using the original MK3 spring still ? And have you kept the large and excessively heavy steel piston weight / top hat (you can see where this is going) ?[/QUOTE]

All sounds encouraging - roll on tomorrow.
Yes, the Mk3 spring, but with Nick TB top hat and guide. ⁹

[Shed tuner]

All sounds encouraging - roll on tomorrow.
Yes, the Mk3 spring, but with Nick TB top hat and guide. ⁹

OK, good that you have thrown the steel lump out and used Nick's TH instead... You may run out of spring spacing and have to use a spring more like that which originally came with the mk2 - i.e. a bit stiffer... but try it and see where you get

[TonyL]

I don't think I am brave enough to try Tony's idea of boiling the whole assembly - has anyone tried it?

I've never had the bottle nor felt the need to try it myself either, Michael.

I'd love to try some comp tube rifles with comp tubes made / finished to known, fine tolerances. Must surely be something to aspire to for many?

Jon's advice is good, as always. See how you go.

But, as and when you did get the chance to have a proper play, I think there would be merit in exploring the ring sealing solutions and playing with different seal carriers / crush etc. But then I understand that rings are less tolerant to inconsistent cylinders, so leading us back there.

Have fun.

[evert]

Maccari has advice on this, less it more ...

https://www.airrifleheadquarters.com...age/251485.htm

Maccaris advice is good, he has some more on sizing under one of his seal listings:
https://www.airrifleheadquarters.com...485/834669.htm

bear in mind a freshly sized seal will wear in very quickly, so do not size to prefection, or it will be too small with a few dozen shots. Size to be too tight, but so you can get it and and move it with a good shove. then shoot 30-40 and it'll probably be fine..

Also good advice. It is very easy to go too far in sizing, looking for the optimal "sliding fit"- and then, after some shooting, the seal ends up undersized.

I prefer a quite high lathe speed when sizing, and using a quite coarse sand paper (180-240 grit). I use it dry, but move it around to avoid clogging.
Try to keep the shape of sealing edges intact.

[charliemow13]

I didn't try boiling for sizing a HW77 seal but after reading that technique somewhere a while back that gave me the idea to hold the piston/seal over a heat gun on low setting and gently warm it while rotating it and taking care not to get it too hot and scorch the seal. Then popped it into the comp tube briefly to size before sliding out and allowing to cool. Found on first attempt that if left in the comp tube to cool down it would contract as it cooled and would end up undersized. Had to reheat and them press the front face of the seal on a flat hard surface (stainless steel plate) to spread the seal and then retry to get the right fit. Always made sure to keep the piston aligned with the axis of the comp tube when sliding it in, or perpendicular to the flat surface when spreading the seal.

[the bish]

I seem to recall that when I fitted a VMach kit to my Pro Sport a few years back, the instructions were not to size the new seal, that it was designed to 'shoot in' and the power would increase gradually as it sized to the compression tube.

[NickG]

I seem to have learned a lot about TX cylinders from this thread, as well as about sizing seals. I certainly was fooled by the cross hatching into assuming it had ben properly honed, but I noticed the tube has clearly been rubbing oppsite the shoe recess. I have no internal mike to check with, but the gun was running with only a few fps variation with the old piston and seal, so any variation in diameter shouldn't be a problem. It is now back together with a tight (but not ridiculously tight, as it was out of the box) seal, but only giving me 9.5 with 42mm preload, I suspect due to the tight seal. I'll put some pellets through it in the garden tomorrow, then see if that improves things.
I don't think I am brave enough to try Tony's idea of boiling the whole assembly - has anyone tried it?

A chap on the other forum has boiled a few hw ones and reports great success.
Michael did you use the piston you had off me , It was standard so you should have been able to just drop the seal on that you were using in that comp tube originally, if its only doing 9 The seal would need to be pretty tight I would be looking at making sure your end cap is sealing.
A word on o rings and cylinder quality, way back when I first started using o rings in the tx I found that they would only make power with a relatively thick cross section, and what I now know to be a high amount of crush (.010" on diameter). The reason for this is to take up the ovality in the tube , The tube I use for reduced cylinders is much better quality wise and allows me to use smaller section rings with a fraction of the crush , so a smaller contact area less friction and the same power for less spring,
The synthetic piston rings are another story all together and surprisingly efficient .

[Shed tuner]

A word on o rings and cylinder quality, way back when I first started using o rings in the tx I found that they would only make power with a relatively thick cross section, and what I now know to be a high amount of crush (.010" on diameter). The reason for this is to take up the ovality in the tube , The tube I use for reduced cylinders is much better quality wise and allows me to use smaller section rings with a fraction of the crush , so a smaller contact area less friction and the same power for less spring.

yup, there's far more choice of seal when sleaving down with half decent quality seamless tube, whether on the TX, HW, PE, anything. I guess with parachute type seals, the manufacturers just didn't bother upping the tolerance, but even with these para seals, you do sometimes get comp tubes that just aren't very efficient, due to air leaking as the seal can only adapt so much / so fast. I did hone (badly) a crap one once and it did gain an extra 0.75 FP afterwards, so a definite improvement (seal sizing was discount after numerous swaps).

The synthetic piston rings are another story all together and surprisingly efficient .

You little tease, you. TonyL will be getting ever so excited (but they do look good)

[Vernal]

[QUOTE=NickG;7940487]A chap on the other forum has boiled a few hw ones and reports great success.
Michael did you use the piston you had off me , It was standard so you should have been able to just drop the seal on that you were using in that comp tube originally, if its only doing 9 The seal would need to be pretty tight I would be looking at making sure your end cap is sealing.

Yes Nick, it is your piston, but I couldn't use the old seal as my piston has a Tinbum nose extension, which uses a Weihrach seal and I didn't have a spare AA. I was getting 11.3 with the old set up, so assume the cylinder is OK. The new seal, from Chambers, was very tight on fitting and still is quite tight after some resizing.
I put 30 shots through it this afternoon, which made no difference at all, so I upped the preload to 45mm which gave me a smidgeon under 10. Tomorrow I shall put lots of shots through it and if that doesn't get me to at least 10.5 I shall have another go at resizing using one of the many helpful methods suggested here - purely because it must be quite inefficient to be under 10 as set up now. On the other hand, it does feel very nice now, and I am getting the most consistent one holers at thirty yards that I have ever had from the TX. Perhaps I shall learn to love it after all.

[Shed tuner]

if you are building this for benchrest, and you are shooting one holers, I'd leave it alone

[NickG]

Michael I have a selection of used tx seals Shall U send you one, I can select one and try it in a brand new tube I have here .