Chemistry help please

[pothunter]

I had a thought after I previously posted, and realise that I got tunnel vision about the seal and O ring becoming fused.

My original degree is Organic Chemistry and, having thought about it, my view is that an essentially inert amine type polymer, ie Nylon seal, or a Butyl compound, O ring, couldn't possible weld to a steel tube, (the butyl would dry out and become brittle).

To throw a variable in, it might be not the seal or the o ring, it could be the amounts of mineral oils and grease that have previously been applied which have dried out and formed a hard semi cross linked gum/polymer as the volatile elements have evaporated.

If you have more of these to do petrol, xylene, plus gas or any dino fuel type liquid might be more successful at bringing the hardened gum back into solution and make freeing easier.

Acetone and Isopropyl may have moved it in this case, but my thoughts are that is is more of a creeping liquid that has disrupted the mechanical bond, rather than any solvent effect.

[edbear2]

I had a thought after I previously posted, and realise that I got tunnel vision about the seal and O ring becoming fused.

My original degree is Organic Chemistry and, having thought about it, my view is that an essentially inert amine type polymer, ie Nylon seal, or a Butyl compound, O ring, couldn't possible weld to a steel tube, (the butyl would dry out and become brittle).

To throw a variable in, it might be not the seal or the o ring, it could be the amounts of mineral oils and grease that have previously been applied which have dried out and formed a hard semi cross linked gum/polymer as the volatile elements have evaporated.

If you have more of these to do petrol, xylene, plus gas or any dino fuel type liquid might be more successful at bringing the hardened gum back into solution and make freeing easier.

Acetone and Isopropyl may have moved it in this case, but my thoughts are that is is more of a creeping liquid that has disrupted the mechanical bond, rather than any solvent effect.

It's not the washer or o ring but the cacky spongy buffer washer behind the piston head, this degrades and expands, I don't know what it is made of as am a welder, but a plasticky slightly spongy stuff a bit like a shock absorber piston bump stop is the best I can do

If you get one and place it in Acetone it goes all slippery when handled, rather than totally dissolve, but again that's all I can add except the Acetone from the cocking slot end does work for me.

ATB, Ed

[PhatMan]

WebleyWombler,

Try a mix of acetone & penetrating oil - 50:50.

Have fun & a good Bank Holiday

Best regards

Russ

[WebleyWombler]

Ok, got them all apart by trying all the methods and suggestions and have come to the conclusion that paint thinners or acetone dripped in from the spring end, left to soak for a couple of hours, coupled with later applied heat via heat gun is the best way to free the pistons off.

both the Meteors have been rebuilt.
the first needed Scotchbright treatment in the aircylinder to shift the final traces of crud and was then treated to a complete Protek refurb kit. The spring had about 30mm pre load. 1 shot through the Chrono with marksman pellets = 7.6FPE. 20 shots into the backstop and it does a very consistent 8.3FPE and shoots well

The Second was a little bit different. As stripped, it had a gold coloured aftermarket spring in with about 25mm preload. it appeared in good condition so was left. Piston 'O' ring was one out of a Lidl kit , buffer washer was 2 x 3mm leather washers cut from an old belt. breech washer was a home made one cast from PT85 casting rubber left to cure for 36 hours. It's a bit soft at shore 85 and i don't know how long it will last but is worth a try.
Before assembly the piston and air cylinder bore was given a liberal spray of the of the cheap graphite lubricant bought from Lidl. this was left for 2 hours for the carrier to evaporate before assembly.
First shot, it dieseled. very badly, scared the crap out of me . 20 shots into the backstop later and back to the chrono. Same 14.2 gr. Marksman Pellets. A reasonably consistent 9.5-9.7FPE and shooting very sweetly with no perceived vibration or bounce. the cheap bits seem to have worked but I'll have to use it more to determine longevity.

The 3 Scorpions can wait for now but I'm going to treat them to different piston heads and see what results I get.

[jedburgh]

A very useful thread .

[JB101]

Another option would be to use acetone and ATF 50:50 which is a very good penetrating fluid to help shift seized nuts and bolts.

Dichloromethane / methylene chloride is also very good at dissolving epoxies and the like but difficult to get hold (as can be nasty) of and evaporates very quickly.where I worked we used to have a pot of it with water on the top to stop evaporation and drop what needed to be cleaned into it and leave it overnight.

[WebleyWombler]

I did try a mix of different solvents and oils but the oil seemed to make things worse, or at least that was my perception. straight solvent such as pain thinners or acetone seems to be best. I have previously tried Hydrogen peroxide down the transfer port in guns that have stuck leather washers. it works well if the washer is dried up but not if it is well oiled, but they rarely get stuck. Its the dry ones that get damp and cause a rust ring to form that causes a problem. I was told about hydrogen peroxide by a long dead retired mechanic who used to refurbish old tyre pumps for the vintage car crowd.

I managed to get hold of an eye dropper bottle full of that Dichloro stuff that cccjgd mentioned. Can't tell whether it worked as it evaporated quickly. The man who gave it me warned me to be careful with it and a safety briefing on it's use. I'll give it a miss as it's not nice stuff and hard for me to obtain. I don't want to ask for more as he is my supplier of tiny quantities of conc. nitric acid which can be useful to remove easy outs, taps and hardened self tapping screws. I don't keep it at home but get it off him on an as needed basis for specific jobs so don't want to be seen as too demanding.

[trajectory]

This thread has thrown up some useful tips & information, could save someone a goodly bit of time messing about.
There are iindeed some nasty chemicals about, never come across a really stuck leather piston washer but thats an interesting solution.

Bye the way has anyone identified what the BSA buffers are actually made of?

[WebleyWombler]

Bye the way has anyone identified what the BSA buffers are actually made of?

I'm not quite sure but rumour has it that it was specially mined for BSA by Wallace and Gromit on their first trip to the moon when they had a supply contract with Feinwerbau to supply seal material for the 300s series. Unfortunately it doesn't travel well and earths atmosphere doesn't seem to agree with it.

Incidentally, I've just realised I wasted a few hours making the concentric punch to cut them out of leather belting. A 1" holesaw in a battery drill cuts them out concentric with only the centre hole needing a little widening to fit the fixing stud , I don't need to make many ATM but this is a quick and easy way of doing it. I've made flat washers for Gems like that but only just thought to try it for the BSA buffers

[trajectory]

[QUOTE=WebleyWombler;8028204]I'm not quite sure but rumour has it that it was specially mined for BSA by Wallace and Gromit on their first trip to the moon when they had a supply contract with Feinwerbau to supply seal material for the 300s series. Unfortunately it doesn't travel well and earths atmosphere doesn't seem to agree with it.


Wonder if they are the same guys that sold that soft grip rubber to the camera companies in the 80s & 90s that degenerated over the years to make a sticky mess?

Migrating flexibiliser?

Concentric seals are fun....been making quad seals so know what its like

[AC99]

I had some success recently in freeing up a seized piston assembly on a Meteor mk5 without dis-assembly by applying cellulose thinners via the cocking slot and allowing it to soak/penetrate for 30 minutes or so. It took a little effort by applying force to the cocking lever to free it up and it operates freely now and works fine.

[trajectory]

Just encountered a stuck BSA piston & was thinking about how I might go about unsticking it.

After removing the stock & telescopic sight i placed the action on a padded surface covered it with a single layer of fabric & then simply placed a hot water bottle over the area where the piston head would be. After 40min or so the piston could be drawn back with what seemed like normal effort. I don't know if this method will work in every case but that was much easier thsn I expected.

Had visions of hot water soaking, solvent blends & all sorts of of things.....

[edbear2]

Just encountered a stuck BSA piston & was thinking about how I might go about unsticking it.

After removing the stock & telescopic sight i placed the action on a padded surface covered it with a single layer of fabric & then simply placed a hot water bottle over the area where the piston head would be. After 40min or so the piston could be drawn back with what seemed like normal effort. I don't know if this method will work in every case but that was much easier thsn I expected.

Had visions of hot water soaking, solvent blends & all sorts of of things.....

Was the hot water bottle full of acetone though

ATB, Ed

[trajectory]

Was the hot water bottle full of acetone though

ATB, Ed

Tee hee......

No, just good old aqua tapis nice n hot.......very pleased how easily it all went & no mess.

[WebleyWombler]

Just encountered a stuck BSA piston & was thinking about how I might go about unsticking it.

After removing the stock & telescopic sight i placed the action on a padded surface covered it with a single layer of fabric & then simply placed a hot water bottle over the area where the piston head would be. After 40min or so the piston could be drawn back with what seemed like normal effort. I don't know if this method will work in every case but that was much easier thsn I expected.

Had visions of hot water soaking, solvent blends & all sorts of of things.....

I've had some success using a heat gun to warm the cylinder round the piston but it seems to only work on the more lightly seized ones. Anything stuck proper solid needs a bit of solvent help, or so it seems.

All contributions welcome, anything that makes life easier is always worth knowing.