Improved model D -Replacing piston washer

[RichardH]

I have a knackered Improved Model D for rebluing/refinishing for an old chap locally, on stripping it there is no piston washer at all just a rivet of some description?

Whats the best way to replace the rivet?

Thanks

Richard

[ggggr]

sure someone will be along to tell you for sure but on the few pre war Bsa underlevers that I have seen, the piston washer has been held on by what appears to be a countersunk head 2ba screw. I have come across two examples where this has broken flush with the piston head and I have centre popped it, drilled very carefully and then tapped to 2ba. (This takes some doing without a vice and with a drill stuck on high speed!)

[RichardH]

Thanks, have drilled out and made a new screw to suit just need a washer now

[targetmark]

I made the one for mine from scrap leather

[Phil Russell]

There is a guide on here that tells you how to make a new leather piston seal. Try a search.

Or if you pm me your e mail I am pretty sure I have a .doc guide on how to do it....... if this helps.

Cheers, Phil

[Lakey]

The set up on the improved Model D, was an outer cup shaped leather piston washer with an inner circular flat leather filler washer, and a brass countersunk washer for the screw to bear against keeping the whole lot tight to the pistonhead. You can buy the whole assembly from John Knibbs if you dont want to make your own, Otherwise you can make the leather washers from ofcuts obtainable from the local shoe repairers, or bits of leather taken from a good thick leather belt.

All the best

Lakey

[edbear2]

As Lakey says regarding replacement......You may have found though, that the "rivet" was the remains of the head of the original screw......I have had a couple like this in the past where repeated use with no, or a disintegrated washer have hammered the screw head flat, but on careful removal (sometimes a blob of weld helps) the original screw thread is still fine. The pistons are a close fit in these guns, so they will still fire a pellet even with no washer, although the almighty "clunk" you get when the piston smashes into the end of the chamber is normally a clue that all is not well

Original / pattern washer set lay out here

On the original unit to the right, you can see where the brass retaining disc has moulded itself to the shape of the transfer port....normally a sign of either a gun that has been fired with no pellet in several times, and so the piston has not been buffered by the column of compressed air behind the pellet, or just long extended use.

P.S. the new ones in the pic are J.Knibbs replacements.

[BadPigeon]

I have purchased a new improved mod D leather seal washer and screw from Chambers and the screw doesnt fit the piston head. Too big. Does anyone know where i can get just the washer screw. Short of that i will need to get a new set from John Knibbs. Dissapointed with Chambers selling really soft looking screw that doesnt fit. Tx boys

[Heavy Roller]

@ Have you spoken to Chambers about the non fitting screw? What did they say?

[BadPigeon]

Not spoken to them yet i have now ordered a John Knibbs set. I found out the screw Chambers sell is probably BSF 3/16 with 32 TPI (threads per inch) i actually counted the threads and 32 is what i got. The actual BSA Screw is 0.1656" dia, 37 TPI and 0.476" to 0.480" long over the threaded part. Got this info from a post titled "Eddie on piston washer screw". I am thinking someone with a lathe could make them selves a big wad of notes selling this and other hard to find parts.

[deejayuu]

BadPigeon 2 BA is nominal 0.1850" so recut to that 'cos screws are easily obtained.
Probably common knowledge but old bike pumps are a useful source of leather cup washers in good nick.
Later versions have synthetic washers but still useful.
Never pass any in boot sales or charity shops if the diameter suits +/- , cheapskate!

[edbear2]

Not spoken to them yet i have now ordered a John Knibbs set. I found out the screw Chambers sell is probably BSF 3/16 with 32 TPI (threads per inch) i actually counted the threads and 32 is what i got. The actual BSA Screw is 0.1656" dia, 37 TPI and 0.476" to 0.480" long over the threaded part. Got this info from a post titled "Eddie on piston washer screw". I am thinking someone with a lathe could make them selves a big wad of notes selling this and other hard to find parts.

Hi, 37 tpi is a mare to do as many lathes are not capable due to gearbox restrictions..And trust me as someone who has access to machinery, that £2-4 for a screw is cheaper than you can do it yourself with most home or small workshop setups..Even if you had a lathe already, you would need to make loads before you broke even, assuming you had the correct thread cutting tips and a way of making a proper job of the screwdriver slot.

I buy all my screws from online suppliers, I might tickle them up a bit, but it's far less hassle and cheaper for the maybe dozen or so per annum I may need.

I normally open out the piston screw if the slightest amount of play, couple of write ups here;

http://www.network54.com/Forum/67044...+washer+screws

http://www.network54.com/Forum/67044...526/Threadform

http://www.network54.com/Forum/67044...ead+reclaiming

John Knibbs, as far as I know, gets screws run up in batches to keep the cost down, the threads and heads are normally very good, but sometimes the bigger pivot and trigger screws can need a bit of trimming, and inletting for keeper screws in the case of the pivot screw.

He may make a quid or two on each one, but he is there with a business to run, and I am grateful he and Chambers are interested to be honest, we do tend to take it for granted sometimes that we can get biits for things that have been out of production for so long!

HTH, Regards Ed

[BadPigeon]

I have now also purchased a John Knibbs washer set and can confirm the screw is a perfect fit so very happy that i can finaly put my rifle together. JK screw is protruding in front of the leather washer so i am worried it might be slamming in the back of the transfer hole. Metal to metal contact cant be good but i might be wrong. I might reduce the insert leather washer or use the chambers main leathe seal with JohnK other bits in which case i got a perfect fit. Couldnt agree more, and i am also very very grateful that these parts are still available for my 104 years old air rifle absolutely amazing. Will purchase few JK spares just in case at the same time still think Chambers clearly selling the wrong screw is disappointing as if this is the missing part you will not be able to put your rifle back together. Tx for the links much appreciated JK as you say is very good value for money no doubt about that.