Piston seal lube. Has there been any change???

[QuigleyUpYonder]

Bryan,
I always hone.

To get the best results from Krytox, you need to thoroughly remove any traces of your old lubricant. Hydrocarbon residue adversely effects the molecular bonding of Krytox, a very desirable quality we are paying for.

Here's what I do:

I like to blast everything clean w/ 3M's HP Brake Cleaner followed by scrubbing with hot soapy water(Dawn), rinsing and then wet hone with 600 grit silicone carbide. The honing is primarily to ensure that you are down to "bare metal" but the cross hatch does helps to retain the lube during break-in. I then use compressed air to blast dry my parts. You need CLEAN, DRY compressed air. I do custom paint jobs (another hobby!) and have a refrigerated dryer with Motor Guard desiccant traps at all points of use drops in my shop. If you don't know what any of that means, don't use compressed air for "drying" your uber cleaned parts. Prior to assembly, I then wipe with DuPont Krytox HC Plus cleaner and then lather everything up lovingly with Krytox.

 
There's very little "break-in".
Depending on how heavy handed you were w/ application and your technique, you will get a very slight discharge from the transfer port into the barrel. This is a BONUS(!) because if you have a properly cleaned barrel, you will then get the "Krytox effect" in your rifling! After the first half tin/tin of pellets, you can run some patches through the barrel to clean it up, check on the results. YMWV with this. I do this after the first couple tins and then don't bother with the barrel anymore unless I develop a problem. After the first tin of pellets, you should start to notice some very nice, CONSISTENT shot strings. I don't get more than 10 fps extreme spread (ten shot string) in a healthy/Quigley tuned gun. Have a few guns that are very consistently 5-6 fps es. Anything more is a bad pellet. Best of luck!

[QuigleyUpYonder]

KevinBrian,
Don't let my post above worry you or make you feel that you need to re-do things.
I didn't go through all that on my first couple guns and still had very good results!
See how your job holds up and then tweak things as you go along.
 

..that's what led to what I wrote above.
Also, I'm just a wee bit touched in the head!

[Bryan Heimann]

I have read that with an O-ring seal, you want a polished cylinder unlike the regular piston seals we use.  I figured that the way this stuff bonds with the metal, in conjunction with the fact that it is not a source of fuel for combustion, it would work best with a polished cylinder- or that perhaps it wouldn't make a difference either way.  I have read that the honing of the cylinder serves 2 purposes- provides a better surface for the moly lubricant to "stick" to in order to create an evenly lubricated surface, and also to provide a tiny amount of fresh moly for fuel on every shot.  That's why I had to ask...

[QuigleyUpYonder]

Bryan,
I forgot about the O-ring scenario!

If you clean like I described, bonding is a non-issue, so don't bother honing if you already have the correct surface finish/roughness. And speaking of that, "polish" is a vague term. What you really need to find out is what the correct RMS/micron rating is supposed to be and compare it to what you have. There are micron rated abrasives (3M) available that can be used to "clean up" the compression tube. May or may not be necessary, just throwing it out there. Most of my experience with machining O-rings is for their use in a static condition as opposed to a truly dynamic one such as this.

[nced]

Here's what I do:

Thanks for the detailed procedure! Yesterday I ordered "Dupont Krytox Standard Gpl 205 Grease, 0.5-ounce Tube" from McMaster Carr and I'm hoping that this stuff will be what I've been searching for. I've been running oring sealed piston caps in my HW springers with great success for over a decade. The issue however has been the propensity of molly paste to diesel and eventually "wear away" at the point of sliding metal parts like the high pressure point of the top skirt of the piston against the receiver tube during cocking.

I'll give my oring sealed R9 the "scrub and Krytox" treatment as do some testing, especially as it pertains to temperature induced poi shifts. I've felt that one of the issues with hydrocarbon based grease like molly paste (basically molly powder in mineral oil) is that the molly paste "out gasses" more at higher atmospheric temperatures than lower so there is a tendency for the poi to shift. Years ago  both my brother and I had a poi shift of 1" at 20 yards during an early spring field target match where the sight-in was done during snow flurries, yet the afternoon temps rose to the 60s. The search was on for more stable early/late season  squirrel hunts and I found that MINIMAL lubing along with oring sealed piston caps mitigated the poi shifts to a great degree. Our (my brother and I) latest lubing scheme has been to use only dry powdered graphite for piston/oring lubing and it does work great (very little temp induced poi shifts), however I have found that I occasionally need to "puff" a bit of extra graphite into the compression tube through the transfer port to keep things sliding free.

I'm hoping that the "$17 for 1/2 oz stuff" would give a good lubricated oring/piston lube without temperature induced poi shifts. Along with the Krytox I also ordered a package of 90 durometer Nitrile orings to try instead of the 70 durometer rings I normally use. In the past I've tried the harder stuff with molly paste lube and found that the softer rings worked better for sealing the varying nature of a R9 compression tube.

For a dynamic oring seal the recommended surface finish of the bottom of the groove and cylinder surface is 32 microinch (smooth honing), and the recommended finish of the sides  of the groove is 63 microinch. Here is a chart of recommended dynamic oring sealing specs......
http://www.allorings.com/gland_dynamic_reciprocating.htm

Here is a chart giving the surface finishes achieved with various cutting methods.......
http://engineershandbook.com/Tables/surfaceroughness.htm

Keep in mind that the high pressure spike of the springer shot cycle is very short (cylinders operate under full pressure for the full length of the stroke) and the mainspring "duty cycle" isn't very long (most springs don't last for 10,000-20,000 shots), the peak pressure isn't really high (perhaps 3000 psi) so I've found that the well fitted oring usually lasts longer than the spring. I can get a 100 count bag of Nitrile orings for less than $5 plus shipping so I usually replace my orings yearly (have occasionally skipped a year without incident) when I do my winter "dustin & cleanin".

Anywhoo......again, thanks for the "how to" info and I'm hoping that the 'spensive Krytox stuff works well enough to nix both the molly paste and the graphite powder.

[kevinbrian]

I  home-honed ( I made a home made........mandrel?) and lightly honed it with 320 grit leaving it very smooth but crosshatched at what appears to be a 60 degree angle, though there is no way of my measuring. I just know that I only ran the hone in and out at a fast speed with drill turning at slower speed. I only made a few passes in and out with transmission fluid as my cutting oil. I then cleaned up everything and checked my work. Like alot like the inside of a TX200 compression tube. 
 I weighed my FTT;'s. They are 11.8 grains. At 830 fps. Over 18 fpe.  No dieseling. No smell of smoke.

[Bryan Heimann]

I never liked the idea of using a brake cylinder hone in my airguns- and I've never invested near as much as some of you into one.  I made a "flapper" for my honing purposes with a wooden dowel and a piece cut from a plastic package that a centerpoint scope came in.  Put a piece of 400 grit in there and honed  tge cylinder evenly even across the cocking slot and etc.  so that the whole tube had a proper cross-hatch for the thin layer of moly to stick to.  Made more sense to me than honing the compression area only, as all the metal on metal contact occurs behind it, after all, and the use of moly for fuel seems like a secondary purpose compared to providing a lubricant between two pieces of steel. 

[nced]

I've been using DuPont Krytox in my springers for over 15 years. 

I wish to personally thank y'ALL for this thread that mentions springer lubing and the Krytox lubes! I have ordered a $17 half oz tube of the "205 stuff" from McMaster Carr and I'm hoping that it will "live up to the billing".

Over the years I've relied on molly paste for my internal lubing, however I have learned from experience that the carrier in the molly paste I've been buying from a couple airgun sources will evaporate over time leaving a kinda gummy substance. LOL....I have a "screw top container" of molly paste bought years ago and over the years the paste became so thick that I ended up thinning it a bit with mineral oil to restore the original thickness. I don't know what the carrier was originally, and the mineral oil did seem to work, however the mix will detonate if it gets in front of the piston seal.

A couple years ago I started messing with dry graphite powder as a piston seal lube so there would be no "age related thickening" and it has worked well for the oring sealed piston cap, however it also seemed to need an occasional "puff" of powder through the transfer port to maintain a "piston to receiver contact" lube. Then I experimented with 6 micron molly powder in place of the graphite and it also seemed to work well, however after a while I would start noticing a SLIGHT "grating action" when cocking. Regular molly paste on the piston skirt would solve the "grating action", but I learned that if the molly paste migrated to the dry graphite lubed oring sealing surface it wasn't so good. I learned that when graphite powder mixed with migrated molly paste, the resulting "sticky gum" would kinda "glue" the piston to the receiver which affected the velocity.

Anywhoo.......IF the Krytox performs as claimed for my applications, then perhaps I've found an all around springer internal grease that will lube everything without excess dieseling (I'm hoping NONE)!

Again, thanks to all contributors to this very interesting thread! My Krytox is on the way and I'm looking foreward to trying it!!     

[nced]

Ed maintains there is no contribution from hydrocarbon fuel or fumes but I will.stick with the Cardews on this one.

LOL....Ed doesn't CLAIM that there is NO contribution.........just that the velocity difference between lubing the piston/receiver of his .177 R9 and .177 HW77 with dry graphite was only 10fps less than when lubing with Maccari molly paste, and the graphite lubed velocity was very consistent. My brother also had about the same velocity drop when he switched to dry graphite. Anywhoo........I don't get NEARLY the velocity increase using molly paste instead of dry graphite as Cardew got with his experiments.

Perhaps this is because Cardew was doing most of his tests with leather sealed HW35 class springers and they REQUIRED the oiling of the seal. I personally don't think that tests of an 8fpe leather sealed springer are NECESSARILY applicable to a synthetic sealed 15fpe springer.

Just My Humble Opinion here! 

[kevinbrian]

In reference to Bryan concerning "brake cylinder honing". I fully agree. Oh I have several including a 400 grit one which feels just as abrasive as the 220 grit. There is no numbering on the sides of the rather inexpensive brake hone stones so who knows. But I did one HW95 tube (compression area only using the "supposed" 400 grit 3 way brake hone and it was too aggressive. I could take a dental pick and lightly scratch the area and FEEL the crosshatching. So I went back to using a wooden dowel with a slit cut in the end for a three inch wide strip of wet/dry 320 grit. It actually leaves a LESS aggressive surface feeling and I can crosshatch the entire length of the tube. They look pretty good and they feel very smooth. And yet I can see the crosshatching. It took some practice and messing up some tubes, but I have finally got to where I can make one feel and look about like a TX200 compression tube (if ya happen to get one that is properly done). With the entire compression tube crosshatched, my 6 piston buttons have a very thin film of Krytox to glide on. I am constantly monitoring my velocity. Still getting 831 fps ave with a VERY low Extreme spread using an unsized Hornet seal (it goes in tight if its dry).  I use a spring of .128 wire. The coils are opened up pretty good so the only spacing I use is about a millimeter and a half on the rear guide. Plastic tophat in front.  The firing cycle is "snick" and that's it. No after shock, after buzz, after nothing. I have it just like I want it. It is 30 yard one hole accurate with FTT's, Exacts, and Barracudas. I think that the Exacts are running at 763 fps average but not sure. I use the FTT's as my standard. Got lots of them.  But when I run my dowel in and out a few times using transmission fluid as a cutting oil/lube, my goal is NOT to alter any dimensions. I ONLY want to score the tube with as nice a pattern as possible for lube retention. I forgot to add that I also VERY LIGHTLY chamfer the inside of the transfer port but I leave the transfer port alone. I've got enough spring power to push the air through that .118 inch port without noticeable rebound. I think that I have got it balanced out pretty good for a rookie.
   But this set up requires an unsized Hornet seal (with this powerful spring). I tried a Vortek red seal that was sized kinda loose but still sealing, and I lost about 20 fps. Don't really know what's going on there. I figured a looser seal made of harder material would be the ticket. But not with THIS particular set up.  The Spring is a Vortek spring from a 2G hw95 kit. The spring wire needs to be the .128 wire. I think some have come with .125 wire. But a good balanced set up could be achieved with that as well. Tight guides. No buzz. Just my rookie opinion. (It's a 20 cal by the way)

[Paul68]

Some of what I've found goes against conventional wisdom so causes issues for some folks. For those who prefer to play it safe, stick with the tried and true methods. They obviously work well judging from their high success rate. If your'e into experimenting, have at it. That said....


I've done a lot of research into the manufacturers of the materials used to make piston and rod seals and what they say regarding their products.

Since interlocking friction is not a significant issue with synthetic seals, the need for a finished surface with strong lubrication retaining properties is reduced. For metallic bores and piston assemblies that utilize synthetic seals, lower RA in the 8-10 range allows better sealing, reduced wear, and lower interlocking friction which results in faster piston assembly response. 320-400 grit depending on the hardness of the metals, will give an 7-10 RA finish. The requirements for wet seal and a self lubricating dry seal are very different, and a lot of what is being applied to airguns seems to be more applicable to wet seal characteristics. High speed pnuematic applications (airguns) are generally dry and rather than wanting to hold any oils, greases or other lubes in the cylinder surface, you want just enough roughness to allow seal material to wear off and adhere. Once that happens, usually after the piston has gone through 100 or so cycles, the roughness in the walls is filled with seal material which acts as lube, and further wearing is greatly reduced. In my opinion, and its only that, any other lube is only a precaution against metal to metal contact, hence the use of moly which is for that purpose and not synthetic to metal contact.

Surface finish depends a lot on the hardness of the metal. A 400 grit stone will not leave the same surface RA on two metals of different hardness.

Also, seal materials impregnated with graphite, teflon seals and other similar extreme low friction materials according to manufacturers can use somewhat smoother finish. This stuff is according to Daemar and Goodyear for those needing reference.

 

[TOM aka critter99]

Please by all means start a thread to follow you Krytox results 

[nced]

Please by all means start a thread to follow you Krytox results 

Be glad to......I'll start one in the "Airgun Gate".

[TOM aka critter99]

Thanks ED I am wanting to follow your results.  You are good on details.  I want to see if you like it as much as I have but I have used a different version with other additives.  The one I listed ingredients on

[nced]

Thanks ED I am wanting to follow your results.  You are good on details.  I want to see if you like it as much as I have but I have used a different version with other additives.  The one I listed ingredients on

Tom, I did a search on the formula you mentioned and couldn't find it to buy in small quantities, however, so far I'm liking the "205 stuff"!

[ericw]

I've been using Krytox in my RWS350 since last May when Pak Protector/Douglas  recommended it and have been very satisfied.
http://www.gatewaytoairguns.org/GTA/index.php?topic=31299.msg290138#msg290138
It is interesting that it took this long to catch the interest of everyone ...better late than never.  Thanks Douglas!
Eric