Do try the 2mm stem, I'd really like to hear the results.
Quote from: rkr on April 09, 2021, 08:43:10 AMDo try the 2mm stem, I'd really like to hear the results.The 2mm stem has around 150 or so rounds through it, so far it is holding up. Putting things into perspective--with the 2mm stem and .270 throat at 3500 psi it maxes out around 1055fps with the Arsenal 257388 87gr . The hammer is in .250" of FREE FLIGHT, zero preload!Generally speaking, I believe a 2mm stemmed peek poppet is good for valves under .300" seat at pressures up to 3500psi. Assuming no more than .300 unsupported stem protrusion, must be a straight line hammer vs hinged swinging hammer, etc.Still testing various things. Will get back to the unregulated Arsenal 257388 testing soon.
A question, what did you use for the stem? I just measured a normal 2mm HSS drill bit and the non fluted part is too short to be a stem for my Evanix.
Quote from: rkr on April 23, 2021, 11:49:14 AMA question, what did you use for the stem? I just measured a normal 2mm HSS drill bit and the non fluted part is too short to be a stem for my Evanix.I cut it with side cutters, then polish the end on a vertical belt sander. I do not harden the tips nor do anything special in attaching it to the peek poppet. Drill a 1/16 hole in the peek, press it in with only an interference fit.
Quote from: mackeral5 on April 23, 2021, 02:21:05 PMQuote from: rkr on April 23, 2021, 11:49:14 AMA question, what did you use for the stem? I just measured a normal 2mm HSS drill bit and the non fluted part is too short to be a stem for my Evanix.I cut it with side cutters, then polish the end on a vertical belt sander. I do not harden the tips nor do anything special in attaching it to the peek poppet. Drill a 1/16 hole in the peek, press it in with only an interference fit. Thanks, ordered some. I was checking M2 grade 12.9 bolts but you can't get them long enough either. Bolts make great valve stems:stem3 by abbababbaccc, on Flickr
I think I'll make a "cup" for the 2mm stem from a piece of 4mm steel rod. It gets glued over the stem end at the poppet end making it 4mm thick there and should prevent the stem from punching through the poppet thus allowing me to use PET-P as the poppet material.
I made a 2mm stem valve for my .224 BSA. Unfortunately it didn't make much difference. I was able to loosen up the hammer spring a bit but there was no big difference I was hoping for. The original stem was 3.2mm so the area was reduced by 60% which should have considerable effect on dwell and the force needed to keep the valve open. BSAs do have very stiff valve springs though, perhaps the valve spring is now the dominating thing in valve closing event?
BSAs do have very stiff valve springs though, perhaps the valve spring is now the dominating thing in valve closing event?
QuoteBSAs do have very stiff valve springs though, perhaps the valve spring is now the dominating thing in valve closing event?That would be my guess.... Where is the smallest port equivalent, both before and after the stem change?....Bob
I don't think there is anything to lose in ditching the spring, if only for testing. I have a couple guns that do not run valve return springs at all.....
Quote from: mackeral5 on May 31, 2021, 04:03:31 PMI don't think there is anything to lose in ditching the spring, if only for testing. I have a couple guns that do not run valve return springs at all.....I tried with no spring and unfortunately self centering valve needs a spring to center, i.e. it didn't seal. It didn't seal with light spring either so I took off some material from poppet to minimize spring tension with original spring and it held air. There was marginal reduction in cocking effort but not what I was hoping for. The problem is partly the Huma gauge/fill valve unit which does not allow quick burst of air in to the cylinder.