The cylinder doesn't leak to outside through the braze --- what you are doing is filling a void within the braze on the inside of the cylinder.
If the braze is porous inside the cylinder between the breech plug and cylinder tube then the pressurised air can pass through the porous braze into the voids in the breech plug.
Here's a debrazed cylinder showing the voids :-
image.jpeg
The voids are machined into the breech plug to hold a mix of brass and flux, this is then pushed into the tube and then heated up to form the brazed joint.
A slight cockup on heating and a porous braze can form allowing air from the cylinder side to enter the void left by the brass and flux.
Hope this helps
All the best Mick
Last edited by T 20; 18-10-2021 at 01:06 PM. Reason: Picture added
thanks guys for the info, feel a lot more confident taking this on now, seems fairly straight forwards...but before i do...quick question, which 35's does this affect?? upto what serial number/year or is it just all 35' with a leather seal, mine is 1980's one of the later ones to be made with leather piston seal as i understand, had the problem been sorted by the 80's?? anyone know? or is it best to do the fix as a precaution anyway whilst fitting new spring an top hat etc, also the conversion parts for changing to a synthetic seal...worth doing? my leather seal looks like new after 24 hours in neats oil.... thanks again fellas
does anyone know up to what year / serial number this problem affected? or is it all hw35's with the leather piston seal? thanks again for the great info
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