Modifying a Webley Junior piston.

Something I have often promised myself that I would investigate,  but never got around to doing so.  There are so many possibles and reasoned theories to look into that it is hard to know quite where to start.  I would really like to hear what your findings are, regardless of how far you are able to take it.  Pity you don't have a chrono. I wish you all the best with the trials and hope you enjoy every moment of it.

Jim.

I'm assuming that Webley experimented with different piston/spring combinations when they designed the pistols and chose the best one? Perhaps you need a more radical re-design to improve performance?

Thanks chaps.   I really cannot see any great improvement being made to a Webley pistol in terms of power.  You might be able to mess about trying to sleeve the transfer port, which probably needs a  message to Shedtuner  on the bbs.   

Ignoring my tinkering  curiousity  with the Webley Junior for now. As far as I know, all the bigger Webley pistols have the same bore and stroke and should have the same swept volume.  I suspect that maybe the transfer port on the Mk1 is shorter than the later guns.  

Therefore it seem odd that you have a Mk1 piston at 68 grams and a Premier piston at 95grams----a 27 gram difference.  I think Tempest /Hurricane ones are about 85 grams. 

If someone really wanted to play about----I'd suggest  3 tests  (1) testing them with the "proper" spring     (2) testing them with a generic spring ------something like Protek sell  (3) swap the non generic springs over.    

That way you should end up with 3 sets of readings for each gun. 

Regarding the heavy Premier piston Danny, I think some Premiers were down in power and they tried a little weight/ insert in the piston before going over to the 95 gram piston.  Regarding springs, David @troubledshooter  has put up pics in the past of genuine Webley springs that are of different specs, for the same gun, that must have come from different suppliers. 

As I've said, I've had a few Tempest pistons modded and one is in the Typest------they are down a little in power but have a very fast firing cycle that I like and so do the other people who have tried them.  

You don't get this sort of stuff on AGF ever since it has been dumbed down.  It's all tarted Tempests and library pictures of a crumbled breech seal on there now 😉  

@JSS.   I'm not expecting anything great with the Junior--it is more a curiousity thing.

Here are some new old stock Senior Springs complete with tags and they are all different lengths. Not much in it admittedly but it does go to show that things weren't always quite as precise as we might assume. 

I've been asking about today about the piston and the way to go about it. My neighbour suggested a cobalt drill with a pilot point-------but the chap who did the Tempest one said an end mill at a slow speed did the job.  

It has been suggested that milling a couple of slots in the piston could lose more weight  (up to 15 grams!) and  that would not reduce preload on the spring. 

I actually want to reduce the preload, even though I think it might not work well. It would be easy to add a couple of washers on the guide to get some of the preload back. If by deepening the recess in the piston by about 6 or 7mm and maybe opening the smaller hole that is already in the piston a bit, drops the weight by around 6 grams that would be ok. A slotted piston can wait for another day of for someone else to try. 

I tend to just try something and see-----rather than going in determined to prove something will work like I hoped.  It can throw up interesting things. 

I suspect that the reduced preload will reduce power and some of the preload will need to be added back. 

I think that the lighter piston (with some preload added back) will produce a faster action.  

BUT----it is a case of wait and see. 

I'm sure most of this stuff has been attempted before, but that the results are not up on the net.  

Hopefully we will get the piston sorted and then have a bit of a tinker and then report back. 

 All joking aside it would help to see a photo regarding the broken off stud extractor (poxy things) but it depends also on what’s available to you. For me with relatively limited tools i might be tempted to drill around it like a core and the chamfer and sweat in a repair section, weld it in and then drill and tap it. Best way of doing it? No….but a possible option for the average shed tinkerer 👍

There is something like an end mill with a hole for drilling round stuff and I've see a video on youtube of a bloke using some sort of tile drill for getting out broken studs.  

I think for the purposes of this experiment------it should be more or less what I'm after-----a lightened piston with a deeper hole and the broken extractor drilled out and the hole tapped to 2ba, which is smaller than the Webley size and will enable me to fit a home made leather washer like the ones I sent you. 

I’m sure you will come up with a suitable solution and save a piston out of it. It wasn’t so long ago that you had been hunting for a Junior piston for quite some time so I’m sure it’ll be put to good use 👍

As the piston was kindly "donated" to me by Doug----and it has that broken extractor in it------I feel this is one to experiment with. If it can be tapped to 2ba it gives me a few options if I wanted to tinker more.   There are not many people interested in this minor tinkering stuff------but it is interesting to me and I do tend to put my findings out there.  As you know there is very little interest in most of it. 

I would say that if a few people tried the lightened piston in a Tempest or Hurricane, that they would like it. Ray liked the Typest, which had the same set up as the Tempest ----(lightened, deepened piston, with the piston washer boss taken off, drilled and tapped 2ba and a leather washer fitted. )

I think the results will be interesting and well worth posting up. It’s borderline anorak stuff but who cares 😎👍

@John G has kindly said he will have a go at this for me. We discussed milling slots in the piston, but I'm not keen , even though it could take off more weight.  As the Tempests etc that have been done, shoot well, I think more or less following that blueprint is a good starting point. reducing weight by 6 or 7 grams or so and less preload on the mainspring.   

If anyone else wants to tinker, it would be interesting to see what a Mk1 or maybe a Senior would chrono at with a Tempest spring and an earlier spring or one of those round wire Protek ones (which i think, may be Typhoon ones and will reduce power in later pistols). 

I'm intending to fit a slightly shallower leather piston washer, but maybe John would like to try an experiment with a thin Ptfe one?  (Premier style).   

I will be interested in how things turn put even if it is a failure. 

Top Man 😎 @John G 👍 

Be interesting to hear about and SEE the results Guy 😬👍

Guy, I did a trade for a Theoben Fenman, Months later I noticed one of the forestock screws was missing, It wouldn't take a replacement as the threads were bunged up with what I thought was a broken stockbolt, I couldn't drill it as it was too hard, It turned out to be a snapped in tap! 😒 

I removed it with a Dremel type rotary thingy, I ground almost through it then shattered it with a pin punch!

Can see the flutes of the tap in the pic after i'd removed a fair bit of it!

And removed..

John is Johnbaz from the BBS by the way!

Posted by: @garvin

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John is Johnbaz from the BBS by the way!

John has an enviable collection and a fantastic amount of photos and only managed x6 posts in 8 years 😆 come on John thas not like you 😉👍 

John G has been busy with the piston. 

This is from a message he sent me the other day/

I have now had a go at milling out the piston. I decided to increase the internal depth by 8mm, and this gave a weight reduction of 6.5 grams. I did not want to go any deeper with the mill as this would put us less than 3mm below the sear ring. However, I did then drill out a central cone with a drill bit, so removing some more metal without have any weakening effect on the sear ring area. So now the piston weighs 63.8 grams, a reduction of 7.4 grams from the original weight of 71.2 grams. (This is the original weight of the piston after I had drilled out the broken extractor, enlarged the hole and threaded it). So in summary you have lost 7.4 grams with a corresponding loss in spring preload of 8mm.

John has also made up a few bits and pieces to enable me to tinker a little bit when I try the gun.

He will probably put up some pictures he has taken as well 🙂  

The piston arrived back today and I had a quick look at it just as it was going dark here.   I tried a Junior that I was going to try the piston in and then I took the piston out and weighed it. It was 75grams with the washer and screw.   The one John sent back weighed in at 69 grams with the old washer I found, and the screw. So 6grams difference. 

The leather washer I tried was out of my spares , as I was not in the mood to make one today. It seemed a bit tight and I had to work it round to get it to into the cylinder. I prefer to fit leather washers dry but as this was an old one I couldn't.   It was a bit tight in the cylinder but I'm hoping it might settle overnight. 

With the washer being  tight and there being 8mm less preload on the mainspring, I didn't think the gun would spit a pellet out, but it did.  (Yay!).  It sounded like the gun was less powerful than before, going off the noise of the pellets hitting the backstop.  The gun was quite easy to cock though with less preload. 

It was almost dark here but I managed to shoot at a dot on a bit of paper and was quite surprised at the grouping, considering how bad the light was. I decided to turn on the outside light, which isn't brilliant and something casts a shadow, near where I shoot.  I shot the end of a tin can twice and then decided to try for a bottle cap. I hit it with all 3 shots, so that is ok. 

There seems little recoil with the gun but obviously it need a longer shoot and a bit of a tinker.  

Going off the Tempests I've done, I'd guess it might need 4 or so mm of preload adding back with washers on the guide-----although John has included a few that will go in the piston, which should not affect weight too much. 

Hopefully, the power will come back to "normal" but the shot cycle will speed up, and the recoil stay fairly low.   More plinking is needed! 

These were the modifications made to the piston that Guy is tinkering with.  The first problem was to remove the broken screw extractor from the piston head.  As this was made of hardened steel  it would have needed a carbide drill to shift it - with the expensive risk of that snapping off too, so I took the easy way out and heat softened the whole piston and jammed screw extractor. The piston was held at 800oC for 5 minutes and then cooled slowly in air.

  You can see here that the extractor has sheared off quite deeply in the hole:

Now that everything had been softened, the extractor was readily drilled out with an ordinary HSS drill bit.  The hole was then enlarged and threaded with a 1BA tap: 

The next stage was to mill out some of the piston head from the interior of the piston so as to make it lighter.  The Junior piston head is quite thick, so there was plenty of metal to go for.  These were the final internal dimensions:

So the weight was reduced by 7.4 grams, and the spring cavity lengthened by 8mm.   

Milling was quit straightforward with a 1/2" carbon steel end mill, as the piston steel was now softened:

The piston was finally re-hardened by heating to 800oC, cooling rapidly in oil, and then tempering at 200oC for 20 minutes. 

To provide means of adjusting the weight of the piston and also the spring pre-load  (the piston interior depth) some PTFE and brass spacers were machined on the lathe.  An inner washer for the leather was also made to accommodate the new 1B seal screw:

So its now over to Guy for some merry tinkering.

Great job and write up John 😎👍

Okay---a quick bit of tinkering and a plink last night and this morning------------and also the realisation  (Once again) that we forget things or don't think straight in the heat of things. 

I wanted to add some preload but do it by adding washers to the guide rather than the piston, so I looked for some washers.  Most of the right size OD have an ID that is too small to go on the guide.  I found something that I thought might do short term, Ie. go on the guide and also go in the cylinder.   So I put a couple on the guide and the gun wouldn't cock. It was then that I remembered  that anything bigger than the OD of the mainspring will foul the back of the piston and stop the gun from cocking DOH!  John mentioned that he didn't have any bigger OD PTFE to make "Power washers" and that is why he did the discs you see to go in the piston.  (maybe that was lost in translation? )   If they had been drilled to go over the guide, they would have been ideal.   

Anyway---I remembered I had some "Power washers" knocking about------but of course they were for a Tempest/ Hurricane and were too big OD for the Junior.  I really didn't fancy trying to file 50 thou off the OD of them. I toyed with the idea of cutting a slot but ruled it out.  

So---I found a couple of small steel washers that would fit in the piston (and loose enough to get out) and tried the the gun.  The power was up a bit and the gun felt ok-----and was surprisingly accurate. 🙂  So I sandwiched one of the solid PTFE washers between 2 plain steel ones and put them in the piston.  The total thickness was 7mm so that was nearly all the pre load back. 

That seemed to up the power a bit and the gun remained accurate.  More plinking is needed to get the right "Feel" for me .  

Regarding the power washers and where to add them, it is swings and roundabouts.  If you add them to the guide, then the the spring has less support by the thickness of the washers. If you add them to the piston, then you are adding weight. My preference is for them to go on the guide as you will see them when you strip the gun. Part of this preference if because of that Junior that was giving me problems and I found a plastic washer stuck in the end of the piston.    Obviously with the piston John has done, I can always undo the piston washer screw and poke them out if they are tight. 

My feelings on this are that you are not really going to get much more power out of a Junior anyway-------even a 10% increase wouldn't really be noticeable. BUT you can make the gun feel a little bit better (to me) .

 John offered to get the weight of the piston down more by doing a few slots in it (I think you said down below 60 grams John? ) --but I didn't want to do too much more that had been done with the Tempest piston. 

John has also mentioned he may be making a piston for a Junior he has that is lacking one ------so it will be interesting to see what he decides on for weight and preload.   I think if another 5 or 6 grams could be removed----------but keep the 69mm depth of the hole in the piston, that it might give a fast cycle and also the room to add  weight or preload. 

A BIG "THANK YOU" to John for helping me cross another of the things off my tinkering list 👍 

I've tried another plink with the gun just now.  I took out the spacers I'd put in the piston and then fiddled  about with the Ptfe spacers that John sent and a couple of steel washers.  I was going to try for less than 5mm but one combination came up at about 5.6mm so I thought I'd try that. 

Again there is no really noticeable power difference, but the thing is bloody accurate  😀  It is also a little bit easier to cock. 

No here is another thing 🙂  Is it accurate because of the lightened piston -----or because the Ptfe inner that John made for the  piston washer is better than the one normally supplied for the Junior and MK1?  

Maybe you should knock up a few more John and put the dimensions up 😉 

There is still some plinking to be done and maybe another mm of spacer to be taken off and tried---------but all in all I'm pretty happy with the experiment. 

There is no great difference in power either way, but there does seem  a bit less recoil, the gun is a bit easier to cock and it is  bloody accurate.  

👍

Not exactly scientific but interesting observations all the same Guy.  It's a pity you do not have a chrono, as it would be nice to know if these small changes have any effect on muzzle velocity.

I have ordered some 3/4" round steel bar, so will soon be starting on making a piston for the Junior I picked up very cheap as it had no piston.  I can post progress on here if of any interest. 

Cheers,

John     

@johng I'd be interested in your piston John.  

I think with a Junior the changes in velocity would be very small anyhow---- but probably, just about measurable.  The Typest was Chronographed and was a little down in power but feels really nice to shoot.    As I only plink I go off "feel" and on some rifles, I fit old springs.  

To some people the power is everything.  

I think of these guns a bit like a car or bike being set up for a small tight circuit, rather than a long smooth one. 

When I briefly had a Chronograph (It died--I didn't kill it). I was getting high readings form a Tempest but I think that was more due to dieseling. That had a Ptfe head and was tried with weights (I had to cut the guide for that 😐 )   ----------------------------Oddly, it was the chronograph dying that set me on the path to lighter pistons and going off  "feel" ------as I just went outside and started to plink at a few dots on a bit of paper.   

I don't think this sort of stuff is of interest to many people --------probably just you, Phil, myself and about 2 or 3 others. 🙄 

John, Guy et all, this area of tinkering is most interesting to me and I am really enjoying the thread and magnificent pictures.  Years ago I watched ( and did a fair bit of my own tinkering ) with sleeves and different springs in Sussex Armoury Jackal rifles in the hopes of taming the early scope-destroying recoil characteristics.  The limitations of case hardened pistons was something of an issue but with a couple of spring and liner combinations dropping the power just a little, definitely reduced the harsh feel of the recoil and made the rifles much more enjoyable to shoot.  In some cases even, more accurate.  Unfortunately, my recall of numbers is very poor and I can't remember the details in ft/Lbs or if the differences between using .177 or .22 cal. were parallel or not.  My main interest was always in .177s as that is what I grew up shooting and was most interested in at the time.  On an aside note, I did a few trials with making D I Y ballistic sleds but the plasticine kept dropping fragments and none were acceptably successful.  I am told by a friend that the Blue Tack type of classroom adhesives work far better than plasticine as an inexpensive visual indication of penetration/power and that Plumbers Putty is even better than that.   Something that might enable an inexpensive comparison of the results achieved by different individuals, tinkering in their home workshops ?

@pjbingham  Agreed and Very nicely done !

FAO JohnG......Hi Prof....I think i've mentioned it before but i've got a fair few "bit's" of airguns kicking around and i'm always happy to help members out with any projects they might be contemplating.As a complete clutz i'm useless at the engineering skills the likes of yourself an Phil have but do enjoy seeing what you get up too...and how you get there.If I can help either of you out i'd gladly do so...and on that front...I found these out tother day some new/unused and others appear to be used.?

I cannot make out the lengths of the pistons. 

Juniors are .750 inch in diameter and the bigger pistols   .7965------.800

If the bigger ones have a big diameter steeped screw they are probably Mk1's

With a smaller screw then they are probably Premiers. 

If they have a boss on for a piston washer , then Tempest etc. 

Lengths in new money, without the screw are approx 83mm for the Junior, 89mm for the Mk1 and 96mm for the Premier. 

I don't think that one on the left is a Junior, but a Gem or something like you sent to me years ago. 

Guy...you win a coconut.... 😆 

Posted by: @hwvixen

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Guy...you win a coconut.... 😆 

I don't like coconuts 🙁   

Posted by: @hwvixen

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FAO JohnG......Hi Prof....I think i've mentioned it before but i've got a fair few "bit's" of airguns kicking around and i'm always happy to help members out with any projects they might be contemplating.As a complete clutz i'm useless at the engineering skills the likes of yourself an Phil have but do enjoy seeing what you get up too...and how you get there.If I can help either of you out i'd gladly do so...and on that front...I found these out tother day some new/unused and others appear to be used.?  

Yes Chris, you made that kind offer a few weeks back.  I never thought to ask if you might have an old Junior piston in your treasure trove, but I am already on my way with making one so it doesn't matter now.  I don't think I can see one in your picture, unless they are all very narrow pistons. It might be worth measuring them and getting the anti-coconut piston guru to identify them for you for future reference. 

Cheers

John 

I had another plink and a tinker with the Junior yesterday and today.  It is an accurate thing. I'd forgotten about the Ptfe spacer and a washer I'd put in the piston, but "Discovered " it again today. 

What I could do with now is getting  someone to part off a few slivers of 12mm or slightly less OD round bar of 2 to 4mm thickness so I can try to put them in the piston, rather than having the washers on the guide, which means less of the mainspring is supported.   I don't want to try the washers that John made for the guide in the piston as if they stuck, they would be a bugger to get out, as I would not be able to remove the piston washer screw and then use a punch, due to the hole in the middle of the washers.  (I still  remember that Junior that gave me an arse kicking, due to a washer stuck down the piston).  Trying to file the OD of the washers is not really on.  

If I cannot scrounge a few of those slivers/ spacers, then the chances are I'll put the Ptfe spacer and a washer in the piston and use it like that as it is nice to use. This is more of a curiosity thing.