HW/Weihrauch R7 compression tube scratches

[EMrider]

I have two R7s, both in .177, and they are my most enjoyable plinking guns. Both guns were purchased new about 10 or 12 years ago. A new ARH kit and vortek piston seal was installed in one of my R7s about six months ago, and it is shooting brilliantly. I opened the other R7 to install the same ARH kit and vortek seal combination last week. This gun had not been opened in 7-8 years and had a vortek pg2 kit inside with at least 15k shots. At some point in this gun's lifetime, the rear of the piston was making contact with the compression chamber. I don't recall when this happened, and suspect I just attributed any roughness in cocking to a 'breaking in' process after I installed the vortek pg2 kit years ago .

The problem I'm left with is that there is a rough/scratched area in the compression tube. These scratches are farther back in the compression tube than the piston's stroke when fired. But they do present a problem when trying to install a new piston seal because I have to push the seal past this rough area and there is high potential for the seal to be nicked or cut.

Can I use sandpaper on a dowel, or some other process, to remove these scratches in the compression tube? Or is the tube just toast? Any input on how others have fixed scratches or abrasions in a compression tube would be appreciated. I don't have a lathe and my plan B is to buy another compression tube from Chambers if there is no viable fix. Thanks.

R

 

[A.G.R]

You are going to use a hand drill and sand paper drums With a extension if need be.. Feathering each way on the sides and around towards the top. You may not get rid of all of it but smooth out the edges so seals are not cut on the way in.


Using a new Vortek kit willl keep the piston centered and stop 95% of any side rub. That being said if you don’t you will need a custom button job to center and stop any future rubbing.. I’m sure the piston skirt shows scratches to that will need to be removed.

 

[EMrider]

You are going to use a hand drill and sand paper drums With a extension if need be.. Feathering each way on the sides and around towards the top. You may not get rid of all of it but smooth out the edges so seals are not cut on the way in.


Using a new Vortek kit willl keep the piston centered and stop 95% of any side rub. That being said if you don’t you will need a custom button job to center and stop any future rubbing.. I’m sure the piston skirt shows scratches to that will need to be removed.

Super helpful, thanks. Any suggestion as to what grit sandpaper might work best?
R

 

[Gerry52]

Emery cloth or SUPER fine grit sandpaper. Work with it til surfaces are SMOOTH.

 

[Bedrock Bob]

Emery cloth is WAY too coarse IMO. It is 120 or coarser. "Super fine grit sandpaper" could mean anything from 320-2000. I don't know the answer but I do know there is an answer.

A good crosshatch pattern about 320-400 grit is what i have always assumed was correct for a cylinder. I hear lots of guys polishing up to 1200 which IMO is probably too fine to hold lubrication.

I don't know the exact answer to the grit question. Ive never honed an airgun cylinder. Im anxious to hear what the experts say about the proper profile.

I do know that Emery will put deep scratches in the tube that will take lots of steps to polish out. Galling leaves divots and high spots. You only want to take off the high spots and not grind down to the bottom of the divots. With a coarse messy paper like Emory you will have deep scratches and tons of grit shedding everywhere. That loose grit will roll over into the low spots and make them deeper.

Having worked with similar cylinders I'd use an appropriate grit wet/dry paper that didn't shed abrasive. I'd work the tops off the galling with 320 on a stiff backing and then hone with 400 and possibly 600 afterwards. Same with the piston. I'd turn the hone slowly and use fast strokes to get about a 30 degree crosshatch. If there are a few divots left that's fine. You just want the ridges of the galling knocked down so there are no peaks to cause friction.

 

[A.G.R]

Emery cloth is WAY too coarse IMO. It is 120 or coarser. "Super fine grit sandpaper" could mean anything from 320-2000. I don't know the answer but I do know there is an answer.

A good crosshatch pattern about 320-400 grit is what i have always assumed was correct for a cylinder. I hear lots of guys polishing up to 1200 which IMO is probably too fine to hold lubrication.

I don't know the exact answer to the grit question. Ive never honed an airgun cylinder. Im anxious to hear what the experts say about the proper profile.

I do know that Emery will put deep scratches in the tube that will take lots of steps to polish out. Galling leaves divots and high spots. You only want to take off the high spots and not grind down to the bottom of the divots. With a coarse messy paper like Emory you will have deep scratches and tons of grit shedding everywhere. That loose grit will roll over into the low spots and make them deeper.

Having worked with similar cylinders I'd use an appropriate grit wet/dry paper that didn't shed abrasive. I'd work the tops off the galling with 320 on a stiff backing and then hone with 400 and possibly 600 afterwards. Same with the piston. I'd turn the hone slowly and use fast strokes to get about a 30 degree crosshatch. If there are a few divots left that's fine. You just want the ridges of the galling knocked down so there are no peaks to cause friction.

The rear area never sees any sealing like the actual compression inner chamber. That’s more sacred than my girls compression tube… you need not worry as much as more so getting all ridges gone or softened enough that the piston seal can pass un cut By them. Once in the piston should have been prepped before to get rid of galling on it.

Buttons or glide would be the best but a PG4 centers pretty well. As long as you prep the shoe.

 

[Bedrock Bob]

The rear area never sees any sealing like the actual compression inner chamber. That’s more sacred than my girls compression tube… you need not worry as much as more so getting all ridges gone or softened enough that the piston seal can pass un cut By them. Once in the piston should have been prepped before to get rid of galling on it.

Buttons or glide would be the best but a PG4 centers pretty well. As long as you prep the shoe.

What grit would you use to hone the comp tube? Do they even need to be honed at all?

How do you prep the shoe?

 

[EMrider]

Quick update. I put the R7 back together using the old vortek piston seal because it still looked good. Was careful when pushing the seal past the scratched part of the compression tube. I just had an opportunity to shoot the R7 today. Using JSB 7.33s, I got 700fps (8fpe) with a SD of 3.5 over 10 shots. That is good enough for me and I'm going to leave it alone for now. At some point I'll go back into the gun and try and fix the scratches as suggested in this thread. Many thanks to those who replied.
R

 

[A.G.R]

Quick update. I put the R7 back together using the old vortek piston seal because it still looked good. Was careful when pushing the seal past the scratched part of the compression tube. I just had an opportunity to shoot the R7 today. Using JSB 7.33s, I got 700fps (8fpe) with a SD of 3.5 over 10 shots. That is good enough for me and I'm going to leave it alone for now. At some point I'll go back into the gun and try and fix the scratches as suggested in this thread. Many thanks to those who replied.
R

8 ft lbs is fantastic.

 

[Bedrock Bob]

That's awesome!

It's good to know the galling isn't up where the seal is running. I was visualizing a sealing problem.

Seems like a periodic lubing with secret sauce might be all you need. As long as things are sliding along I guess there isn't a problem.

 

[Motorhead]

I would NEVER SAND to an extent of removing a heavy scratch or gouge !!!
Ball hone the entire length of tube I.D. Polish tail of piston then do what ever service, resealing etc ...
Assemble with appropriate lubes and your done.

Heavy sanding/ honing you have created an out of round tube and one much looser & likely tapered.

 

[Bedrock Bob]

I would NEVER SAND to an extent of removing a heavy scratch or gouge !!!
Ball hone the entire length of tube I.D. Polish tail of piston then do what ever service, resealing etc ...
Assemble with appropriate lubes and your done.

Heavy sanding/ honing you have created an out of round tube and one much looser & likely tapered.

What grit ball hone do you use?

 

[A.G.R]

I would NEVER SAND to an extent of removing a heavy scratch or gouge !!!
Ball hone the entire length of tube I.D. Polish tail of piston then do what ever service, resealing etc ...
Assemble with appropriate lubes and your done.

Heavy sanding/ honing you have created an out of round tube and one much looser & likely tapered.

You may not, but sanding and polishing the rear section is the only way to remove a gouge. Ball Hone will not and WILL HANG UP IN THE SLOT ,OR ROUND IT OFF ..



The rear section has very LITTLE to do with anything other than smoothly cocking and fireing
As stated , a Vortek kit would be needed to center the piston after the stem was centered. or better fully glided skirt.
ball hone is not good for the chamber area as it only gets as close to the radius of the ball to the chamber face. LEAVING A RIDGE OF UNHONED CHAMBER.
There are better ways , Sunnen being the best but you can make tooling that will duplicate it if your creative.

 

[Bedrock Bob]

Galling is a series of divots followed by peaks. It's pretty easy to knock off the peaks without changing dimension or getting things out of round. A stone or abrasive on a hard backing is only going to hit the high spots.

A ball hone profiles the surface for sealing and lubrication. It won't take much off the peaks. It follows irregularities. A hone that uses three stones would help straighten things up better but still... it's only meant to profile the surface.

I've never honed an airgun cylinder. But I've honed a lot of cylinders. If you have a few pits it's not much of an issue. High spots are the problem with galling. An abrasive sheet or paste on a hard rubber or plastic backing only hits the high spots and dosent affect the bore dimension at all if you are careful. A stone or ball hone works on the full circumference. By the time you get the high spots knocked off with a hone your bore will be much bigger. A few strokes with paper in the right spot and your not honing the whole bore trying to get a group of ridges out. Your just taking off the high spots.

I've always considered a ball hone or a 3 stone cylinder hone as surface prep. Not a straightening or flattening tool.

I'm not convinced honing an airgun cylinder is needed at all. Again I don't know squat about air rifles and I may be completely wrong. I've never heard an argument for doing it unless the surface needed dressing up from rust or damage. The compression tubes I've peeked into looked like a well honed surface that didn't need any attention. I'm not sure why I would hone it.

 

[Motorhead]

What grit ball hone do you use?

All my ball hones are many years old and IIRC started life @ 240's, tho as they wear there grit aggressiveness becomes less & acting more along the lines of @ 320's.
With using ball hones a bit one direction then the other direction works ideal, as this breaks and smooths high spots or ridges seldom effecting the original bore specification.

Flat stone hones ( Sunnen etc .. ) will make a flat and even surface no doubt, but at the cost of lost material. Being these are NOT engine cylinders with cast iron / chrome rings doing the sealing ... but a flexible piston seal and as such a straight & true surface just is not required.
At the Piston tail wear end area of comp tube all we need is the two surface to not be in conflict on profile ( being near equal radius and smooth ) having then the lubricant used be the medium preventing wear and scuffing from the axial loads & vibration/ shuttering during the shot cycle ( Moly or like lubes )

 

[Bedrock Bob]

All my ball hones are many years old and IIRC started life @ 240's, tho as they wear there grit aggressiveness becomes less & acting more along the lines of @ 320's.
With using ball hones a bit one direction then the other direction works ideal, as this breaks and smooths high spots or ridges seldom effecting the original bore specification.

Flat stone hones ( Sunnen etc .. ) will make a flat and even surface no doubt, but at the cost of lost material. Being these are NOT engine cylinders with cast iron / chrome rings doing the sealing ... but a flexible piston seal and as such a straight & true surface just is not required.
At the Piston tail wear end area of comp tube all we need is the two surface to not be in conflict on profile ( being near equal radius and smooth ) having then the lubricant used be the medium preventing wear and scuffing from the axial loads & vibration/ shuttering during the shot cycle ( Moly or like lubes )

Awesome Motorhead. Excellent info.