Extra Breech O-Ring ??
I,ve noticed that when the time comes to replace the breech o-rings (90 Duro Viton) on my Stealth,,that the air leakage seems to be greater at the barrel end of the breech slider. The top-hat end usually seems to be OK. The barrel is a LW,,supplied by Leupy and the breech area is in perfect polished condition. I wondered if the short,fast movement of the breech, when firing, over that part of the barrel is causing accelerated wear ? If so,,has anyone fitted a second o-ring,,next to the existing one,,to at least delay the wear a little? Its not a major problem,,just something else to fiddle with really,,but I would be interested to hear peoples views.
All Replies
10Bears,
I think the 33 is “gamer talk” for EE. I doubt the 33K means anything.
For silicone oil go to your local hobby store and get some silicone shock absorber oil for radio control cars. I have it in 10, 20, 30 and other weights. R/C cars use o-rings in the shocks, and they want them to be free and slick, so the oil might be the right trick.
HTH
Jim
Walter,
I found in ebay that Dow is selling a product called SLEEK or actually, SL33K for paint ball bolts.
Not sure if the 33K is a reference to centistokes/viscosity or what. I’ll give it a try and let you know what it’s like and if it seems to have any effect on consistency.
Larry
Walter,
Thank you very much for the info. I’ll hunt some down…
Cheers,
Larry
I think I now at least have contact using the o-ring with the .070″ thickness now.
I’m now wondering if the LW barrel snout is undersize. Will have to mike it the next time it’s out.
I was going to order another breech block (bolt) from AF to send to Tony for the anti slap mod, so it’ll also be interesting to see if that one fits better (not rattle fit) using nominal thickness o-rings.
L
10 bears, I use Dow Corning 55 oring grease which is quite soft.
I would try a silicone oil if you can find some as well.
Cheers,
Walter….
Reduced stiction makes sense due to the location and function. I think it probably rules out double o-ringing it… and the metric solution as well.
CNC doesn’t mean zero tolerance in any sense, especially in a production environment. Still, the trend seems to indicate it is intentional in this case. Reasons given for why this is so make sense to me. Perhaps some leakage in this area is inevitable and acceptable.
Regarding consistency, the diver’s silicone I have is possibly too heavy. Can someone suggest a brand or source of something a bit more like a gel and less like a grease?
Thanks,
L
10b
You might look at metric o-rings. A 2mm cross section would be 0.079, where you’re seeing 0.070 be a bit loose. I imagine the 2mm will be too tight, but it might be worth a try. Since it’s inside a bore, the ol’ “stretch it to make it thinner” trick won’t work worth a crap.
I think the last thing it might be is sloppy machine work. It’s a CNC part, someone went to the trouble to make the grooves different for a reason that no doubt seemed important to them at the time. It’s not an accident that they all seem to be that way.
Another point is the fit of the rings when they’re not under pressure is probably not the issue at all. Think about it. Both rings see exactly the same pressure, and have to seal at that pressure, but one of them has to slide during the firing cycle and one doesn’t. Big difference. o-rings generally shift under pressure, contacting on three points and depending on being deformed by the pressure they’re holding. As that happens, one of those three points (against the barrel extension OD) has to slide.
Make it too tight and consistency and therefore accuracy is going to suffer. Make it too loose, and leaks give you problems.
But the fit is not an accident, IMO.
Doug Owen
Well said Doug, was hoping someone would pick up on the difference.
I make mine a nice easy sliding fit on the barrel as any stiction there will tend to slow the valve closing. If the oring is in nice sliding contact with the barrel when the pressure pulse hits it teh oring will seal fine.
As you point out the tophat fit is static and so can be tighter to a degree.
I must be able to slide on/off the barrel stub easily for cocking the gun but can indeed fit ‘tight’ on teh tophat.
If it was me the tophat would be made say 0.010″ larger than the barrel stub and the breech cuts and fits could then be the same.
Take care and shoot often 🙂
Walter….
I think the last thing it might be is sloppy machine work. It’s a CNC part, someone went to the trouble to make the grooves different for a reason that no doubt seemed important to them at the time. It’s not an accident that they all seem to be that way.
Another point is the fit of the rings when they’re not under pressure is probably not the issue at all. Think about it. Both rings see exactly the same pressure, and have to seal at that pressure, but one of them has to slide during the firing cycle and one doesn’t. Big difference. o-rings generally shift under pressure, contacting on three points and depending on being deformed by the pressure they’re holding. As that happens, one of those three points (against the barrel extension OD) has to slide.
Make it too tight and consistency and therefore accuracy is going to suffer. Make it too loose, and leaks give you problems.
But the fit is not an accident, IMO.
Doug Owen
I also noticed that the o-ring groove at the front of the bolt was looser.
I measured an assortment of -011 o-rings. Hard finding the urethane 90 duro orings (yellow ones), but they were smallest of all anyway. No good there.
I measured a bunch of black 90 duro o-rings and the ring thickness varied from .066″ to .070″.
I installed the thickest one on the barrel end. It reduced noise and perceived air leakage. It certainly did not eliminate it. It doesn’t “feel” tight, but it does finally feel just slightly snug.
I wonder if it’s sloppy machine work… or if AF maybe did this to make barrel changes easier. Frankly, I don’t think it would be a problem installing a barrel even if it was much tighter than this!
I wonder if Tony can machine a second groove at the barrel end…?
Larry
10b
Here’s a strange thing; if you try the fit of the breech slide over the barrel then the front 0-ring seems to be quite loose,,even with a new 0-ring. Yet,,if you slide the breech on,,the wrong way round ie. top hat end forward,,,then the fit is a lot tighter. I tried this with two different breeches and got the same result. Could the 0-ring groove at the top-hat end be machined a little shallower on purpose,,for some reason?? Or,,is it just poor quality control? Either way,,the top-hat o-ring groove is the size I shall use for the second o-ring experiment,,,at the barrel end.
Lol, i read that you are in the Forces, you sure your not a salesman!!?? 😆
If you had a tank, you’d need a lot more ammo!
I sooooo need a tank. This Hills pump is giving me ‘chimp arms’ 😆
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Jim,
Thank you for the suggestion. I’ll give it a try..
Larry
10b