compression tube abrasion

[Tom1340]

About a year ago, cocking my R9 started feeling "rough". When I pulled it apart, there was a long worn path under the piston, about 1/4" wide and couple inches long, at the very bottom, aft end of the compression tube.  The length of the worn area extended along the path of the cocking shoe, from the uncocked to cocked position. It did not reach forward into the compression section of the tube.   I buffed it up with some emery cloth, applied a new layer of Krytox, and went back to shooting.  So today, I think i felt the roughness in cocking again.  Has anyone had this experience... is it normal?
When I got the gun 3 years ago, I went all in on Krytox, thinking the simplicity of a single, non-detonating grease for all parts of the gun was a good idea.  Since then, I reverted to moly for the locking wedge and the breech pivot.  It may have been the way I applied the krytox, but the locking wedge became stiff and required disassembly and regreassing more than once. Since using moly...smooth as silk.
So, when I go back into the gun, do I lube the piston and abraided area of the compression tube with krytox, or switch to moly?   Thanks for your input.

[Roadworthy]

You could try some "Old School Buttons" from Air Rifle Headquarters.  Apply near the bottom of the piston, one on either side of the worn spot about 120 degrees apart.  The third one goes on the side of the cocking shoe.  This will hopefully prevent the piston from digging any further into the compression tube.  You will have to sand the buttons to fit into the compression tube.  I have become a believer in Krytox as a lube.  You do need to strip off all old oil based lubricants before using it and it can be used in conjunction with molybdenum disulfide powder but not moly lube.  If you have used Krytox in the gun it cannot be easily removed as it kind of bonds with the metal.

[Mark 611]

I would try to figure out what is causing the galling, is there any sharp edges? on the cocking shoe? you may need to replace the shoe! galling like your describing is caused by a fitment issue or something out of alignment or loose or to tight or a ruff finish, the notch where the shoe fits on the cocking arm may not be allowing the shoe to slide at the proper angle, as far as lubes use whatever you feel comfortable with, I use the dino lubes, JM moly, I have not ever used the space lubes so can't give any advice on it,

[Bayman]

Is there a kit in there? and did you swap the cocking shoe?

[Tom1340]

I find no evidence of sharp edges, roughness or other irregularities on the piston or shoe (both are original to the gun).  The spring is ARH hornet and the seal is Vortek.  It seems obvious that the pressure of the cocking arm is pressing the back side of the piston (opposite the shoe) into the tube wall and it is apparently dragging due to insufficient lube.  The buttons would be a good fix, in theory, but I question how durable they would be. 
I know many members have had success with Krytox (I used GPL205). But my experience with it on the wedge was not good.  After a period of time, the wedge stopped sliding easily, and the last inch of closing the barrel met with much resistance.  Maybe I put too little of the Krytox on the wedge and in its cavity, or maybe my amazon purchase is counterfeit.
Unless I come up with a better idea, I will probably switch to moly paste in the compression tube on next tear down.  I had good luck removing the wedge area Krytox with warm water and dawn dishwashing liquid.
Just wondering, do your guns show any evidence of wear similar to mine, or are your well used compression tubes still showing a slick blued surface?  My gun has well north of 10,000 shots thru it.
Thanks for your comments.

[Denby95]

If you can get some pictures, it might help people giving you better recommendations on cause and remedy.

[Jason_Garvin]

Without pictures I assume it is the top rear of the piston?  This is a high pressure point in a break barrel cocking.  I seen a HW30 wear here once pretty good, as rumor has it they have a softer piston than the larger HW’s.  I never ran it to work and hit it with a hardness tester to verify.

I have not used space lubes and doubt I ever will.  The only lube I won’t use again is heavy tar from ARH, I found it did dry out and is a mess to deal with.

I do like ARH euro tar and mainly his cold weather tar, which looks like a super high content moly open bearing grease.  Good stuff!

Vortek lubes I use on Vortek kits, never an issue.

I have used ARH buttons to take up slack in some rifles, and have not been back into them too see how they hold up.  I have found some rifles you drop a piston in and they will have more rattle (gap between the piston skirt and i.d. of comp tube) and benefit from using buttons.  Some rifles have better fit and may not really need any.

However, when going back together with the piston in the forward position, I reach through the cocking slot (before the spring is installed) and paint lube on the top inside of the comp tube, from the rear skirt back about an inch.  I have found this to work well for me on that high pressure area.

Jason

[Yogi]

I know many members have had success with Krytox (I used GPL205). But my experience with it on the wedge was not good.  After a period of time, the wedge stopped sliding easily, and the last inch of closing the barrel met with much resistance.  Maybe I put too little of the Krytox on the wedge and in its cavity, or maybe my amazon purchase is counterfeit.

The issue with the barrel wedge is because you did not remove ALL the old moly grease.  Your gun needs to be "operating room clean" before you use the Krytox.
I use brake cleaner, then acetone, then 90%+ alcohol.  With lots of scrubbing during each phase. repeat rinse.  Blame it on user application error.

My HW 50 pistons show similar wear in that area.  I polish with 400 grit, then 600 grit and lube generously.  The buttons should work.  Or find a machinest bubby and have him/her make a deep grove and them install a ring bushing.  Or just live with it...

-Y

[Bayman]

The wear is where the top of the piston skirt rides on the compression tube? I thought it was along the cocking shoe path. Typically I polish out the piston skirts and don't have this problem. There's little load on the compression tube walls. Unless you have too much spring then cocking force deflects to compression tube roof and can cause galling.  IMO Krytox isn't good for extreme metal to metal pressure. I only use moly paste for pivot and detent parts. I've used Krytox for pison lube

[tjk]

A wooden dowel and some wet dry paper can be your best friend for this. I have experienced that metal particles can and do migrate within the compression tube. Most likely your still have some deburring and polishing to do on the cocking slot. These particles can scatter around some during the firing cycle and the spring virbration etc. Being that the top surface area of the piston skirt and compression tube being an inherently tight contact point, from the mechanical movement, any grit of metal particles will be felt to give that gritting effect,…if I said that correctly. Some folks use a dremile tool to grind the cocking slot edges but that can be risking. I prefer to use nailfiles, sponge wet dry pads. Etc. I even stole my girlfriends finger nail buffing polishing pads to really clean up these edges. They work great for buffing out rough spots in the comp tube and piston skirts too,  to a mirror finish. I also use the polishing pads on cocking arm ends and shoes when required. Hth’s 😎

[nced]

I know many members have had success with Krytox (I used GPL205). But my experience with it on the wedge was not good.  After a period of time, the wedge stopped sliding easily, and the last inch of closing the barrel met with much resistance.  Maybe I put too little of the Krytox on the wedge and in its cavity, or maybe my amazon purchase is counterfeit.

The issue with the barrel wedge is because you did not remove ALL the old moly grease.  Your gun needs to be "operating room clean" before you use the Krytox.
I use brake cleaner, then acetone, then 90%+ alcohol.  With lots of scrubbing during each phase. repeat rinse.  Blame it on user application error.

My HW 50 pistons show similar wear in that area.  I polish with 400 grit, then 600 grit and lube generously.  The buttons should work.  Or find a machinest bubby and have him/her make a deep grove and them install a ring bushing.  Or just live with it...

-Y

For the early years of my springer lubing I used "molly paste" and was/is good springer lube "no harm-no foul" with CAREFUL "thin film application". Excess molly paste application to internal WILL cause dieseling and even detonation. I started using Krytox years ago when reading about it's use on an airgun forum and decided to try it out. I preferred Krytox (tried several different versions including Ultimox) settling on the "Plain Jane" GPL205/105 over the molly paste used for years previously. Krytox is non-dieseling, non-drying/thickening, application is less critical, less messy and Krytox doesn't "stain black".
The last HW95 I bought came direct from HW with a "gritty cocking". For a few years now I always break down my new HW springers to replace the factory grease with Krytox (GPL205 for sliding parts and GPL105 for pressed in parts like the cocking lever rivet). I found that the source of the rough cocking was a "swarf & grit" in the spring loaded barrel latching "chisel" like this..............

Cleaning out the detent mounting hole in the pivot block plus removing the grit from the spring, then re-lubing the detent with Krytox GPL205 solved the "gritty plunger syndrome". I've never used any dieseling prone dinosaur grease based molly lubes in this HW95 and the ccking/latching has been "snickety slick" for the years since. Here is a pic I just took of my HW95 Krytox greased barrel latch (Oct14,2023) and it looks like this.......

LOL....I don't get "twisted in a knot" by using a bit of excess Krytox on my barrel latching geometry because the stuff doesn't promote dieseling. I've never had any "receiver galling issues" however the HW piston skirts are case hardened which makes a "dissimilar metal" sliding surface against the softer receiver tube to minimize galling. LOL, I've had HW piston "shells" that were as much as .015 "outta round" and piston latch rod ends that were as much as .060ish offcenter with the piston skirt (probably due to the way the latch rods were "crimped" to the piston head..........

The eccentric latch rod is an easy fix by centering the piston in my 4 jaw lathe chuck, carefully adjust the chuck so the piston skirt runout is minimal, then bending the latch rod till the runout in the lathe is about .005 or less. The "obround" piston shell/skirt was remedied by adding "structural plastic" buttons to the piston skirt glued into milled recesses. LOL, I learned that the HW piston skirts were case hardened because I had to use a solid carbide endmill to create a flat bottomed pocket in the skirt. The buttons were glued into the recesses with "SuperGlue", then the protruding ends were lathe turned so they centered the piston skirt with a sliding fit.

HW95 receiver tubes can also have constrictions and expansions along the length. The older HW receivers that were "hand honed" on occasion would have the bore expanded at the transfer port  when the operator "fell asleep" on the hone. This wasn't an issue with the older rubber parachute seals but made the installation of an oring sealed piston cap unsuccessful due to the requirement for more precise internal diameters when trying to seal with a size 020 oring. I mage up a "go-nogo" gage to test the receiver internal geometry before going through hassles of "piston massaging". If the gage would slide the whole length of the receiver tube the receiver was considered to be good for an oring sealed piston cap.........

[SpiralGroove]

As Jason said, A pic would really help answer the question .

[Tom1340]

The cocking stroke returned to smooth operation the day after I posted my query.  So the roughness I thought I felt may have been the result of a long shooting session on a particularly warm day, or perhaps it was a particle as mentioned by tjk.  I do not intend to open the gun now, unless the feeling returns.  And if there is a loose particle in there, I hope it is residing harmlessly in a void.
Even if this particular issue is behind me, I will eventually open the gun for some other reason.  When I do, I'll post a photo of the tube, showing the abraided strip. 
Thanks...

[Mark 611]

Glad to hear your problem has disappeared for now, myself personally when I get a new gun, I test fire it and make sure its mechanically sound and is accurate, then I tear it apart! I completely deburr the compression tube and all the internal parts, I drop in a new kit and piston seal, most of the time! These rifles really need this work done to them to remove the factory lubes and cleaned up for long term use, JMO, the search eng is not working at this time but you can pull up a thread on a tune I did on my HW50 in .20cal to get an idea of what I'm talking about

[nced]

Glad to hear your problem has disappeared for now, myself personally when I get a new gun, I test fire it and make sure its mechanically sound and is accurate, then I tear it apart! I completely deburr the compression tube and all the internal parts, I drop in a new kit and piston seal, most of the time! These rifles really need this work done to them to remove the factory lubes and cleaned up for long term use, JMO, the search eng is not working at this time but you can pull up a thread on a tune I did on my HW50 in .20cal to get an idea of what I'm talking about

Exactly the same procedure I used whe I received a new HW springer. Years ago I found that the factory HW springs and piston seals "weren't the best" (when shooting 10,000 shots per year at that time). Latest .177 HW95 disassembled and ready for factory lube stripping and relubing............
 

[SpiralGroove]

Glad to hear your problem has disappeared for now, myself personally when I get a new gun, I test fire it and make sure its mechanically sound and is accurate, then I tear it apart! I completely deburr the compression tube and all the internal parts, I drop in a new kit and piston seal, most of the time! These rifles really need this work done to them to remove the factory lubes and cleaned up for long term use, JMO, the search eng is not working at this time but you can pull up a thread on a tune I did on my HW50 in .20cal to get an idea of what I'm talking about

Yeah Master Yoda ,
I pretty much do the same, except I just drop in a ARH/Vortek spring and make a top-hat, spring guide check/correction.

I spend about 2 days, de-buring the receiver/polishing every sliding steel part (trigger too) so that future work will be relegated to the replacing the spring/piston seal only .... as needed.
The bliss on shooting a nicely tuned gun from day 1 can't be overstated .
 

[Mark 611]

Agreed! Years ago, HW's use to hone the tubes from the factory, especially the Beeman models, 

[Bayman]

Agreed! Years ago, HW's use to hone the tubes from the factory, especially the Beeman models, 

Yep now they're terrible. On the new guns you can tell they use seamed tubing because you can see the seam the down the whole length of the compression tube. That's really bad on a piston gun.

[nced]

Agreed! Years ago, HW's use to hone the tubes from the factory, especially the Beeman models, 

Yep now they're terrible. On the new guns you can tell they use seamed tubing because you can see the seam the down the whole length of the compression tube. That's really bad on a piston gun.

Interesting because I used to "hone" (actually smooth out) the factory HW honing using oiled 500 grit wet-or-dry on a home made PVC mandrel for use with the oring sealed piston caps I made. The last HW springer I bought was a new .177 HW95 that was on sale from AOA a few years ago at $295 (I think) plus shipping, however I did have to wait a while for a new delivery to AOA from HW.

As normal, the first thing I did was to break down the HW95 and strip the factory lubes and then re-lube with Krytox. When the receiver was stripped of all factory lubes I was surprised to see the surface finish inside of the receiver looked similar to the receivers after I had done some "home smoothing". Here is a pic of the "unmolested"  receiver ID of the HW95 after the "grease strip"..........


A common "adjustment" with my older R9s was piston latch rod centering and on occasion "buttoning" the piston skirts if excessively "oval". Well, the newer HW95 I received from AOA had a very good piston that fit the receiver tube nicely so only the piston skirt was smoothed a bit. Tthe piston latch rod didn't need centering contrary every other piston with one measuring .060 runout needing centering. HW95 piston as received and after a bit of "skirt smoothing"........

.
I've been wondering if I just happened to get a "good one" or is the fit & finish of most later HW95s similar.

[bustachip]

Who else agrees that Ed has the best HW pictorials
and tuning advice on the inner screen..lol? I’m still shooting one of his aluminum o-ring piston seals in my HW97K. It was installed years ago, with only one tear down and o-ring swap, which was not really needed but I had it apart. I really ought to do a tear down and refresh, but it’s shooting so good I can’t bring myself to doing it..lol.
Here’s to Ed for all of his HW mods and advice and help over the years. Thanks buddy.
Regards, Thomas M.