Sizing seals in springers

[Vernal]

Could I please ask the experienced tuners for advice on which abrasive to use for sizing seals in springers?
New seals are almost invariably a very tight fit in the cylinder, and I know from experience how much this reduces energy, so I do like to get them to a better fit. I am reluctant to use wet and dry, as I worry about grit particles becoming embedded in the seal and working on the cylinder, diamond plates just do not seem to remove anything, and I worry again that maintaining pressure to try and get more action raises the temperature too much. Files seem a bit drastic, and might leave a poor finish, so what should I use please?

[Phil Russell]

I am surprised there have not been more replies .... I do not class myself as a tuner when compared with recognised masters of the art but I have sized a few seals in the past, although mostly home made leather ones.
For a modern synthetic I have rarely needed to ... but that does not mean it is not needed at times. When I have done it I have used maybe 600 grade wet and dry, used dry ... engineers can weep at this point. I think it important to have a means of turning the seal e.g. mounting the piston in a lathe or a 'mounted' electric drill and going very carefully. Mounting the piston plus seal in a hand held electric drill and bringing the seal into contact with the grit paper could work but is somewhat imprecise as it is not as controllable as if the drill is mounted. Check for size often, remembering that the seal will invariably bed in after a short time and you do not want to remove too much and preferably none from the outer lip of a 'parachute' seal. While doing this I take care to wipe the seal after each 'treatment' and, when satisfied I have the size right, clean the cylinder, seal and piston thoroughly before final reassembly. I have never used a file on a synthetic seal.
Leather is different as my home made ones invariably need resizing. Depending on what needs to be removed I have used a lathe with a sharp cutter or even a file before finishing with dry 600. It is possible to size leather by hand as well provided you go slowly. Leather is more forgiving in this regard.
Good luck.
Cheers, Phil

[Hsing-ee]

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

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

[Shed tuner]

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..

[Vernal]

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

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

Very helpful thank you. Confirms that I should put it in with a tightish fit then keep a careful eye on the chrono for the first few hundred shots.

[Shed tuner]

also depends what kind of firing cycle you want.. generally, a somewhat tight fit will give a softer cycle, at the expense of some efficiency...

[Vernal]

While I like a soft cycle Jon, what I am looking for is greatest accuracy off the bench, which probably means a faster cycle, so I am just fitting a Mk 2 latch rod in my Mk 3 TX, as recommended by you and Nick at the Norfolk Bash. Back together and off to the range for testing on Tuesday.

[TonyL]

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

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

Very helpful thank you. Confirms that I should put it in with a tightish fit then keep a careful eye on the chrono for the first few hundred shots.

Yep, useful indeed.

[TonyL]

Graham Henderson, one of the lovely chaps of notable fame from the springers-in-FT days, told me that many of the top shots wth sliding comp tube guns would boil the cylinder and piston & seal assembly to conform the seal to the cylinder without the use of abrasives etc.

.......But also that a sloppier fit would follow quicker than that of an unsized seal.

So you could try this method on the TX?

Maybe this could also be used on rifles that don't have a sliding comp tube by obtaining a short piece of tube with the correct ID and boiling the seal in that?

Personally I haven't ever felt the need to size, just allowing them to run-in naturally whilst keeping my eye on the power. But then I've not had one that I considered far too tight........

However, when I worked on the Mercury S a few months ago I did go for the Meteor 'O' ring for a far less tight fit.......

Mike, NickG has done some pretty awesome work with 'O' rings and 'X' rings. With the ease of strip-down on the TX I ponder whether it might be worth experimenting with home made carriers and the rings for sealing if you have plentiful playtime? Er.......I seem to remember him playing with a different material also recently?

Hope this provides a little more food for thought.

[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.

[Vernal]

I am surprised there have not been more replies .... I do not class myself as a tuner when compared with recognised masters of the art but I have sized a few seals in the past, although mostly home made leather ones.
For a modern synthetic I have rarely needed to ... but that does not mean it is not needed at times. When I have done it I have used maybe 600 grade wet and dry, used dry ... engineers can weep at this point. I think it important to have a means of turning the seal e.g. mounting the piston in a lathe or a 'mounted' electric drill and going very carefully. Mounting the piston plus seal in a hand held electric drill and bringing the seal into contact with the grit paper could work but is somewhat imprecise as it is not as controllable as if the drill is mounted. Check for size often, remembering that the seal will invariably bed in after a short time and you do not want to remove too much and preferably none from the outer lip of a 'parachute' seal. While doing this I take care to wipe the seal after each 'treatment' and, when satisfied I have the size right, clean the cylinder, seal and piston thoroughly before final reassembly. I have never used a file on a synthetic seal.
Leather is different as my home made ones invariably need resizing. Depending on what needs to be removed I have used a lathe with a sharp cutter or even a file before finishing with dry 600. It is possible to size leather by hand as well provided you go slowly. Leather is more forgiving in this regard.
Good luck.
Cheers, Phil

Thank you Phil, I have been running it in my woodworking lathe, which has a four jaw chuck, but only using a diamond plate. If you have never had problems with 600 wet and dry I will give it a go, but it may not need much more now that I have read Jon's comments - I may have been aiming for too loose a fit.