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All Springer/NP/PCP Air Gun Discussion General > Vintage Air Gun Gate

Resealing valve stems

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Jirushi:
Recently I bought a small lathe.
I am experimenting with making polyurethane seals.
Have made a few so far that work, using UK expert seal maker Lawrie Amatruda's technique:
http://anotherairgunblog.blogspot.com/2015/01/how-lawrie-amatruda-makes-polyurethane.html

I find it difficult to cut through the polyurethane shore 90 rod though (to part the seal). I use new surgical blades from the vet practice I work for.

Another technique is to turn an oversize seal in the lathe, and work it with the Dremel until it has the correct diameter.
A friend here in Holland uses tap washers for this technique.



I am going to try to reseal a few valve stems with pressed in stems.
Like Crosman 180, 600.
Not 100% sure if the stems are pressed in, but I do think so. Does anyone know for sure?
I tried to press the stem out with this Proxxon Micro press, but it didn't work. I might need a stronger press.
I have been advised against tapping the stem out.

Instead of removing the stem, I could also burn the old seal out, make a new seal, and push it over the "lip" of the stem?

fivestar45:
I am reasonably sure that the Crosman 150, 160, and 180 all have the stem seal pressed in place by the stem.  You may want to use more force. The problem is if the stem is not extra tight in the brass the  co2 pressure can force it rearward resulting in short stroking, and leakage.

oldair:
The Crosman stems are indeed pressed in.  Some folks routinely push them out with an arbor press no problem, using a suitable fixture to support the brass head.  I think with 90 or 95 Duro urethane you would not be able to 'squish' a seal into place without disassembly.  By the way, I've found 80 Duro is too soft for CO2 seals - they deform under pressure and do not give full power output.

Don R.

eeler1:
Careful Louis, machining takes you down a whole 'nother rabbit hole.  But, it does feel pretty good to make your own parts and seals. And thanks for the link to the amatruda blog, I'll have to go back and take a more detailed look.

I made some wannabee steroid valve stems for some old Benjamins and Sheridan recently.  But rather than re-use of the old stems, I bought some drill rod of the proper dimension, and the made the seals on the lathe, including drilling a hole for the valve stem that didn't quite go all the way through.  Then lastly press in the stem with a very minute coating of glue.  Seems to work ok, but I am still monitoring for long term use.  I was worried that the stem wouldn't be perpendicular to the seal, but it hasn't been an issue.  Parting is not a problem as you are machining the face on the tailstock end, then forming the base that goes into the spring, i.e., even if the parting end isn't perfect, it doesn't matter since all that end does is sit in the spring.

For seals with a center hole, like what you are doing, I'll just pry out the old seal, or burn it out if it is stubborn.  I've never punched out the old stem, but if you can get it all back perpedicular when you are done that would be a good way too.  Probably have to make a fixture to get it just right when pressing it back in.

To make the center-hole seal itself, I made a fixture, with the od maybe a few thousandths over the final od of the seal.  Punch or cut out the seal material oversizee and drill the center hole, then mount several pieces in the fixture.  The fixture is threaded with the bolt the same size as the valve stem.  I put dykem blue on the fixture.  When turned down until the blue is just gone and no more, then the seal is essentially the correct od for the valve body and the hole is centered perfectly.  Only thing to consider is that squeezing the material can cause it to expand, and then when you take it out it 'un-squeezes' and is undersized.  For most seal material you don't have to tighten much and it will still machine without spinning in the fixture.  The harder the material, the less of a problem this is.

Anyway, just some thoughts on how one person goes about some of this stuff.  Probably lots of possibilities that will work.

Jirushi:
Thank you gents for the replies.
The micro press is not strong enough. I will look into an arbor press.
Very interesting to see different ways to make seals.
@eeler1, the technique with the fixture is very smart!
I have lots of practicing to do, but it would be nice to be able to do my own reseals, without ordering or sending valve stems across the globe.

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