Webley Senior piston repair?

[ggggr]

I have a problem with a Webley Senior piston. The holding face where the sear engages is worn and rounded, probably due to cocking link wear a long time ago.

ive got 2 ideas for a "fix" and would appreciate views about how to go about it.

(1) get the front of the piston machined down and then fit a new front end , holding ring and head onto it.
I think the problem with this is how much "meat" is behind the holding ring---IE- how deep the piston is drilled for the mainspring.

(2) Get the ring welded up and then cleaned up. Is this possible? Use Mig or Tig?


Im hoping Edbear might see the "Edbear signal"

[trajectory]

I think if you are filling in a ring/groove then it's probably Mig rather than Tig that might be best. Don't really think Tig will fill anything like Mig as Mig uses a filler 'rod', just choose a filler metal with similar characteristics to the steel the piston is made from. Ok, sounds easier than it might be to do well but think that's the way I'd go. Hopefully you will get some other advice & be able to choose which way you tackle it.

[trajectory]

If it would still work & function safely with a wider groove what about truing it up on a lathe rather than trying to build it up with weld?

I don't know how or what the pistons were made of but it will probably mess up any hardened bearing surface it had....maybe someone can advise you on that. Welding will mess it up too.

[ggggr]

A bit of a bump up for this please

[Vic Thompson]

Firstly a link to a Dealers Website that shows a picture of a Webley Senior Piston : https://www.airgunspares.com/s3weble...tolpiston.html

Secondly, I don't know the extent of the damage to the holding ring but is it possible to just trim back the "rounded off edge by a few thousands of an inch" and then re-harden it to avoid problems with "skin hardening". Having thought about it a few times, if it works it might save a lot of trouble and time over other ways of tackling the job.

Just a thought and apologies if a useless one.

Vic Thompson.

[DrGunn]

Depending on how badly worn / rounded the holding face it it may be possible to just skim it to square it up again, this would be by far the simplest option.
If its badly worn then it should be possible to build it up with weld and machine it back, it may be difficult to to achieve the right level of hardness though so the new holding face will wear faster.

[ggggr]

Thanks to Vic and Matt. I've had the skimming done in the past with a Mk1 piston and it seems to have worked. However on this piston, the ring is not very thick (wide) and fairly rounded as well. Taking it back would mean it would be like a razor blade.

I hope our welding genius Edbear ( who could probably weld spaghetti to string ) will see this and advise.
Another option would be to machine a new head from the holding ring forward and fit that after taking the exisiting bits off. A simlar idea would be to take it down to a core and then fit a sleeve and re machine.

[trajectory]

Looks like the truing it up option seems to be the front runner at the moment, providing there is enough meat on the piston to work with & allow it to still function. There's still the re hardening issue to tackle though. As I said I am not sure what the pistons were made of so can't really advise you on heat treating (if appropriate).

When you asked about welding I went down the Mig route....Tig could work with a filler rod but as there may be more Mig set ups in sheds than Tig ones I thought Mig was a fair bet.

I suppose if it's kaput at the moment then truing it up (& heat treating?) to see if you can get the required hardness might be an option. If it didn't work then taking off a few thou might not effect the possibility of welding, shaping & heat treating as a follow up?

Atb

[Graemevw]

I wonder if you could have the area stellite welded. Would avoid having to mess around with any potential heat treatment.

[rancidtom]

You could certainly build it up with either MIG, TIG or even MMA as I would suspect this is not a fancy grade of steel and nor is it hardened/tempered or case hardened. The easy way to find out is see if a file bites (on a part that isn't a bearing surface!) If these pistons were hardened and tempered I would expect a ground surface finish, the Webley pistol pistons I've seen are not ground but turned, there doesn't appear to be any heat treatment after turning so I suspect they are a mild or low carbon steel as they are easier to machine than medium or high carbon steels and unless they are meant to be hardened after turning there's no need for high carbon steel.
If you wanted to make the built up ring a bit harder than mild steel ask for a stainless steel filler rod/wire to be used, it will produce a higher chrome alloy content that dilutes into the parent metal and so long as the weld is not cooled too quickly it should not be brittle, just tougher and more wear resistant.
There are many recipes of stainless rods that are suitable for this, you could even ask for a hard facing rod to be used but there's no need to make a piston skirt (or latch ring) too hard, it only makes it more difficult to machine after welding. If a very hard alloy is chosen it'd have to be ground to size rather than turned in a lathe.

[edbear2]

Tom's given a pretty good overview to be fair, I would add in general the file test is not the best as even heat treated and tempered 4130 to give nearly 100 Rockwall will file readily with a sharp file with clean swarf.

You also need to test in the worn area, as per Tom's comment about localised hardening, It may well be the rod is an elevated carbon steel (in normal condition) for it's length and flame / induction hardened at the end even.

As for welding, then first preference is TIG then MMA, MIG only if the operator knows what they are doing, maybe with a bit of preheat and set on globular / edge of spray transfer......most home hobby sets don't have this fine control I have found.

With TIG you (if you have a foot pedal like all proper sets should) can control the weld pool and add filler just as needed, knowing that you have perfect fusion, and can also cool the weld under the gas shield if you have a gas delay (or seperate feed set up).

With MIG it's pretty much point and shoot and everything has to be set up perfectly plus filler wire types are very limited on hobby sets, and a 15kg reel for a proper mig set of 309 stainless or HF600 hardfacing will set you back £250-300+

Filler, well you coud just go mild steel if the rod is soft all over, so A15 triple de-oxidised.

Or you could use an alloy steel like 4130 to give slightly elevated strength if worried, HF600 wire which is hardfacing or stainless 309 which is a rod used to join stainless to mild, most other grades of stainless are problematic so avoid.

Or lastly Stellite with TIG, but you will need to grind this as very tough, and again there is a risk of cracking and seperation if not done right.

However on sears / triggers / piston latches, I use the "palo della chiatta" formula ..ie. don't touch with a barge pole!


In the past I have reshaped the sear to suit a reshaped piston rod where it has been worn, or made new rods from old ones by filing a new profile.

But without knowing 100% by either a "zap" test or other what I am welding I won't attempt any repair on a load bearing surface thse days, have seen too many nasties and even if the owner is happy taking the risk, it may let go in the future on someone else.

ATB, Ed

[ggggr]

Thank you chaps

I know what you mean about something happening in the future Ed , but there is not much chance of me getting rid of a Webley pistol.
When I've done a gun, it usually stays on the table in "quarantine" for a good while until Im happy with it. I know that sometimes things just happen, or break , without signs or the problem being there before.
On some guns I like a light trigger, but they are not guns I would trust people with until they have showed they can be safe with a gun. Also, some guns, I prefer the trigger to be quite heavy, especially when trying to teach someone to shoot.

I had a couple of "rogue" Premier Mk2 frames--------where the sear pin hole was in the wrong place. As they were not great frames anyway, I sent them someone who made them into an ornament . Id much rather that, than them ending up on the bay and someone else having a problem that could be dangerous.

[rancidtom]

Ed mentioned stellite, many years ago (back when I were still a spotty teen) I was taught how to stellite camshafts with oxy-acetylene. The last time I repaired a trigger sear I had access to oxy-acet so that whas my choice, given that stellite will manage cam shaft duty I thought it would work as a trigger sear. It worked well, produced a good tough face that didn't crack when stuck a lightish blow with a hammer (the HW100 trigger sear doesn't have a huge load on it so I was happy with this test). It's still working fine many years down the line.
As to stelliting a Webley piston, I've pulled an old piston out of my spares drawer. There seems to be no sign of heat treatment on it, it files easily so I would say it's mild or annealed (before machining) low to medium carbon equivalent, I have no hardness testing files available so can't be any more specific than this and I can't imagine why Webley might go to the expense of making a piston from anything but easy to machine steel and certainly not bother with needing to anneal unless it was absolutely necessary. The piston I found was from an early straight grip Senior. One day I'll get around to repairing it! I'll make a new sear out of gauge plate when I get around to it...
I'm not sure I would use stellite to repair a piston, even in a low power pistol such as these there's a significantly bigger spring than the hammer spring in a PCP and as such it may be too much to guarantee stellite had no HAZ weakness in the dilution zone although careful pre and post heating with a slow cool should minimise this risk it's something I wouldn't like to try.

[WebleyWombler]

As to stelliting a Webley piston, I've pulled an old piston out of my spares drawer. There seems to be no sign of heat treatment on it, it files easily so I would say it's mild or annealed (before machining) low to medium carbon equivalent, I have no hardness testing files available so can't be any more specific than this and I can't imagine why Webley might go to the expense of making a piston from anything but easy to machine steel and certainly not bother with needing to anneal unless it was absolutely necessary.

I have repaired quite a few of them and made new ones as well . I have never come across one that was made from anything other then mild or low carbon steel either. When converting one to either 'O' ring or conventional leather seal (the latter not worth the effort in my opinion) . A parachute seal trial is on the cards if I can get one of the correct size. 3/4" hydraulic ram seals are about 15 thou too small and don't perform well.

I would just back up the bent with a piston ring , double split and brazed to the piston, then recut the original one but removing an equivalant amount off the front of the piston if needed after trial

In a previous life I was a Lloyds/ASME IX welder and have stellited many camshafts for motorcycle tuning and racing but would never do it to a Webley piston. The piston is easier to make than a sear is so would rather the piston wore first. The effect of either wearing is the same so why make life harder?

[rancidtom]

I have repaired quite a few of them and made new ones as well . I have never come across one that was made from anything other then mild or low carbon steel either. When converting one to either 'O' ring or conventional leather seal (the latter not worth the effort in my opinion) . A parachute seal trial is on the cards if I can get one of the correct size. 3/4" hydraulic ram seals are about 15 thou too small and don't perform well.

I would just back up the bent with a piston ring , double split and brazed to the piston, then recut the original one but removing an equivalant amount off the front of the piston if needed after trial

In a previous life I was a Lloyds/ASME IX welder and have stellited many camshafts for motorcycle tuning and racing but would never do it to a Webley piston. The piston is easier to make than a sear is so would rather the piston wore first. The effect of either wearing is the same so why make life harder?

I agree, I really didn't think it would be anything other than a low carbon steel as there's no need and the higher carbon steels only make for more difficult machining. As you mention, brazing a ring on is a perfectly acceptable method followed by a skim and facing operation but it's not really any different to building up a ring of steel filler rod (or wire) which still has to be stuck in the lathe to get it to the right diameter with a square shoulder for the sear to lock on and a ramped edge to make cockiing/latching easier.