BSA Cadet - Breech Seals

[david9d]

I'm busy fixing up a much neglected Cadet Major, a real horror story of Fenland Farmers Bodges, stripped threads - home made piston washers - a spring from heaven knows what - home brew front sight - but a challenge. It needs a new breech seal too - has anyone tried making one?
I have tried leather, but getting thick enough material is a problem, and gluing two layers of thinner stuff didn't work when cutting at an angle.
I tried O rings glued onto an old leather seal, and that failed - or at least the glue did.
Looking at my trusty HW35E I noticed the breech seal is a white plastic, so switch on the lathe and the latest version is from an engineering plastic "Acetal", and trimmed it to length 0.025" proud of the barrel. This seems promising and has lasted for over 50 shots, but I think it is too hard to seal properly.
So what I really need to know now is what material would you suggest to make a new breech seal ?
A further thought - how about a new piston washer made from PTFE ?
All suggestions welcome - apart from throw it in the scrap bin.
David

[edbear2]

Hi David.........I tried all the thinks you did,plus went begging around saddle makers etc. for really thick leather......then broke open the piggy bank and bought a proper one from John Knibbs!......not the easiest type to fit, but once in and trimmed it was fine..there was a thread on here a few months back with some good hints, maybe worth searching?

[BTDT]

,,,so switch on the lathe and the latest version is from an engineering plastic "Acetal", and trimmed it to length 0.025" proud of the barrel. This seems promising and has lasted for over 50 shots, but I think it is too hard to seal properly.

I've done exactly the same with a Cadet Major - turned a breech seal from Acetal. A softer material would be better, but it seems to seal OK, after I spend ages scraping it down to just proud of the breech block.

[royalscotsgrays]

hi if you are not to fussy about keeping things original i have used tap washers as you can cut them down to fit and they do a good job.i put one on my cadet and it shoots very well and they are only 99p to £1.99 for a pack of 4.i hope this is of some help regards mark

[Phil Russell]

Another vore for tap washers.

If you prefer to use leather you may find it easier to get a smal set of leather punches to cut the washer and the central hole. I got a bit of 'hide' from a leather bag making shop and it works well when I want to go the leather route. Or have a walk around a car boot sale ...or a charity shop ... for belts, bags etc
Cheers, Phil

[Mike95]

I tried a piece of leather bootlace and gave up! Get two O rings correct size...clean out the breechseal opening thoroughly. Put first O ring in with a litle superglue...put in some translucent silicone sealer on top of the first O ring and allow it to go tacky. Push the second O ring into the silicone until you get the corect level above the metal...clean off any surplus silicone...leave gun broken to dry out the silicone thoroughly (in airing cupboard etc). First one I did failed beacause I did not leave it long enough. Second attempt worked fine still working fine.

I have wondered if some of the "instant gasket" for cars could be used to make workable breech seals.

Mike95

[david9d]

Many thanks for all the helpful suggestions. Several options are now available to me so I feel a bit spoilt for choice, but as I look after 7 Cadets/Majors within the family I will no doubt try them all at some stage. Of the options my thoughts are (in no particular order):-

PTFE - the material is ordered, so when that arrives I will make a seal up. If such plastic had been available in 1948 perhaps BSA would have used it. Simple to make and easy to fit.

Tap Washers - sadly not thick enough for this application, but look good for other guns or Cadet Piston Buffer washers.

Leather - not easy to get it thick enough for this problem, needs to be over 1/4" thick and not easy to shape - a bit like a tube.

O rings - sounds good when it works, but silicone sealer can be messy stuff to squeeze into a small hole accurately, and superglue can be a challenge too.

Instant Gasket - interesting. Not sure how this would stand up to the pressure radially, or how long it would be effective after being opened and closed many times. Worth a try as I have had success with silicone bathroom sealer as an exhaust gasket on a racing two stroke motorcycle (see my website www.lomil.co.uk for details)

Has anyone tried making PTFE piston washers ?

Thanks again
David

[BTDT]

See pages 65-67 of this month's (April 2009) Airgun World for photos of the seal I made for my Cadet Major.

[david9d]

Thanks "BTDT" I have just arrived home and found my copy of AGW has been delivered, and in it is an excellent review of these guns.
Ironically I went shopping for shoelaces, and in Sleaford found a good old fashioned cobbler who has presented me with an offcut of thick leather.
I may be knee deep in breech washers soon !!
David

[Retracted_Yeti]

Chambers list the breech seal for £5.18 ya tight gits!

Cheers.

Ry.

[red bob]

i can make them sizewise ok bu getting thick enough leather is the problem,
i knock them out in a power press but the stripper that comes down after the punch compresses the leather,so if any one has got the leather of suitable thickness allowing for some compression send it to me.
bob.

[mallyally]

I've done exactly the same with a Cadet Major - turned a breech seal from Acetal. A softer material would be better, but it seems to seal OK, after I spend ages scraping it down to just proud of the breech block.

i made onefor my BSF S 70 you have to do a lot of scraping to get a good seal but you get better barrel alignment on that model with a nylon seal as with the leather one the barrel tends to go upward as it softens

[Mike95]

The problem with buying a leather one is that you still have to trim it to size because the cut out is not the same depth all round ...same prob on the HW55 leather breech washer. Two O rings and some silicone sealant...problem solved. I put 90 pellets throught my gun recently and the breech seal was fine.
Mike