hw 35 leaking breech fix

[Phil Russell]

Here are the comments I made after doing just this job: (copied from my post of around Sept 2011)

The results



JB Weld arrived yesterday and was applied to the cylinder mid afternoon. I used a length of wooden dowel to transfer the liquid weld to the bottom of the cylinder, having first plugged the transfer port. I managed to avoid blobs catching the cylinder wall. Once a blob was at the base of the cylinder I smeared it around the base of the cylinder and then used a thin dowel to effectively push it into the cylinder / end block join. I was surprised at how much I had to use before I could convince myself I had filled the void ... I made up two quantities of weld so must have added about 1ml. I stopped when I could see a small rim of weld all around the circumference. Some weld was unavoidably left on the end block top.
This afternoon I sanded the exces weld away, using emery paper discs held onto a plastic rod with double sided sticky tape. The rod was just under the internal diameter of the cylinder. It took time .. a few slow rotations then removing the rod to brush off the powdered weld ... but eventually I had sanded down to the end of the block. I then added a thin rim of emery paper around the outside of the rod so as to remove any weld that may have stuck to the cylinder walls at the junction with the block. Worked down to a very fine emery grade. Total sanding time about 2 hours. Cleaned out cylinder and inspection with a light suggested all was well ... a nice ring of weld around the block / cylinder junction.
Re-assembled the rifle. First with the very weak spring I had used before. Immediate increase of about 70fps to give around 8 - 8.5 ftlbs (.177). Firtted a stronger spring and rifle is now a pretty consistent 11 ft lbs. Not too bad for a HW35.

So ... thank you all for the advice you gave. The effort was well worth it and the 'void issue' is one I will look for in future. I wonder if other makes of rifle can suffer the same problem?

Cheers, Phil

[forks]

thanks for the advice guys..... i gotta take my 35 aprt to get a new spring in, guess i may as well do this at the same time, i have chrono'd it an its only putting out around 400 fps with super domes.... the leather washer looks like new but the spring is bent, i reckon new spring, guide an top hat, plus plug the leaky breech an it'll be better than new,

[bigtoe01]

capillary action works best under vacuum...the loctite seeks out holes etc.

a modification to the method would be create a vacuum for 30 mins, release the piston, withdraw the TP plug, withdraw the piston, replace the TP plug but this time from the inside of the action, then push the piston back in to pressurise the cylinder.


I have done one 35 this way and 2 35's with just vacuum , and all 3 had the issue cured

[Big Seth]

capillary action works best under vacuum...the loctite seeks out holes etc.

a modification to the method would be create a vacuum for 30 mins, release the piston, withdraw the TP plug, withdraw the piston, replace the TP plug but this time from the inside of the action, then push the piston back in to pressurise the cylinder.


I have done one 35 this way and 2 35's with just vacuum , and all 3 had the issue cured

I am quite sure you got the results you were after but how can you maintain any vacuum by withdrawing the piston if the breech weld is porous? Sorry for my pedantry

[bigtoe01]

I am quite sure you got the results you were after but how can you maintain any vacuum by withdrawing the piston if the breech weld is porous? Sorry for my pedantry

the loctite seals it up

[T 20]

I am quite sure you got the results you were after but how can you maintain any vacuum by withdrawing the piston if the breech weld is porous? Sorry for my pedantry

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

[Big Seth]

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 :-

http://i1138.photobucket.com/albums/...12006666-1.jpg

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

Thanks, now I understand. Regards Ian

[forks]

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

[forks]

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

[TonyL]

Revived for contemporary assistance.