HW/Weihrauch HW35 Leather Piston Seal Assembly

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jaykb49

jaykb49

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Feb 17, 2021
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Bellevue, WA, United States
I have an older (1970?) HW35 that has been converted to a plastic piston seal. I want to change it back to a leather seal. I have the leather seal on order but I can't find the other parts I need. From pictures, it looks like I would need a plastic cup like part to fit inside the leather seal and a round nut to thread on and hold everything together. I can make the parts but I need the dimensions. Does anyone have any of these lying around that could measure them for me? I assume every time a conversion kit is sold someone has these leftover parts.

Thanks for your help,

Jay
 
I have a 1980-vintage HW 35 in pieces at the moment.

I haven't dismantled the seal assembly, but the inner synthetic cup is 23mm in diameter, and the steel retainer is 18mm. It appears to be threaded onto a stud in the face of the piston.
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MDriskill said:
I have a 1980-vintage HW 35 in pieces at the moment.

I haven't dismantled the seal assembly, but the inner synthetic cup is 23mm in diameter, and the steel retainer is 18mm. It appears to be threaded onto a stud in the face of the piston.
View attachment 510835

View attachment 510834
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That "stud" is the other end of the latch rod. BSA did a similar nut on the 1930's underlevers. The nut can be flush with the seal because the piston bounces off the air cushion before it comes to rest on the end of the cylinder
 
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KWK, is it normal for the threaded rod to have a gap in the front as big as mine? Seems like quite a chunk of lost volume. I went through this gun with a JM spring and lubes many years ago; it cocks smoothly and has a pleasant quick, crisp shot cycle, but has always been very low on power.

People smarter than me have suggested using a gap-filling thread lock liquid around the front of the cylinder, to compensate for leaky brazing of the front plug. I plan to try that.

I was also surprised by the transfer port size. I have HW 35's made in 1967, 1973, and 1980. The '67 one has a 4mm port, but the other two are 3mm, and all three have leather piston seals. I had assumed the smaller port came sometime after the switch to plastic seals, but apparently it was the other way around.
IMG_5845.jpeg
 
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MDriskill said:
KWK, is it normal for the threaded rod to have a gap in the front as big as mine? Seems like quite a chunk of lost volume. I went through this gun with a JM spring and lubes many years ago; it cocks smoothly and has a pleasant quick, crisp shot cycle, but has always been very low on power.

People smarter than me have suggested using a gap-filling thread lock liquid around the front of the cylinder, to compensate for leaky brazing of the front plug. I plan to try that.

I was also surprised by the transfer port size. I have HW 35's made in 1967, 1973, and 1980. The '67 one has a 4mm port, but the other two are 3mm, and all three have leather piston seals.
View attachment 510907
Click to expand...
I read on that not long ago on the transfer port size , but my fuzzy brain I can't recall where I read that article . Maybe be vintage air guns ? Anyway someone has a explanation on it somewhere..
 
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Hateful McNasty said:
I read on that not long ago on the transfer port size , but my fuzzy brain I can't recall where I read that article . Maybe be vintage air guns ? Anyway someone has a explanation on it somewhere..
Click to expand...
IIRC, the gist of that thread (which I can't find at the moment either), was an insightful post by Mycapt65, explaining that the 3mm port works better with plastic piston seals, but a 4mm one better suits the lube-burning tendencies of leather seals.

I believe all current HW's have the newer, smaller, 3mm port. So I was surprised to see them on leather-sealed HW 35's from 1973 and 1980.
 
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MDriskill said:
Good morning, HN! 😁

IIRC, the gist of that thread, was that the 3mm port is better suited to plastic piston seals, but the 4mm one is better for the lube-burning tendencies of leather seals. I believe all current HW's have the 3mm port, but I was surprised to see it on a leather-sealed gun 50+ years old.
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You kinda got to wonder part crossover.

Like throw in the old 4mm leather tubes on the first new synthetic ones to save money and clear inventory space ? 😜
 
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MDriskill said:
KWK, is it normal for the threaded rod to have a gap in the front as big as mine? Seems like quite a chunk of lost volume. I went through this gun with a JM spring and lubes many years ago; it cocks smoothly and has a pleasant quick, crisp shot cycle, but has always been very low on power.

People smarter than me have suggested using a gap-filling thread lock liquid around the front of the cylinder, to compensate for leaky brazing of the front plug. I plan to try that.

I was also surprised by the transfer port size. I have HW 35's made in 1967, 1973, and 1980. The '67 one has a 4mm port, but the other two are 3mm, and all three have leather piston seals.
View attachment 510907
Click to expand...
I've seen that thread and the nut badly damaged from dry firing on old BSA's. The rod could have been shortened to remove a squished section. That amount of space probably does't hurt anything. If you think it's going to be an issue fill it in with epoxy.
 
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KWK said:
I've seen that thread and the nut badly damaged from dry firing on old BSA's. The rod could have been shortened to remove a squished section. That amount of space probably does't hurt anything. If you think it's going to be an issue fill it in with epoxy.
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All the HW35's I've had apart were flush. Interesting that it still has the notch where the nut was staked. If it was shortened because of damage there would be no notch. Are the latch rods threaded into front of the piston and could a previous owner have backed it out for whatever reason?
 
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KWK said:
I've seen that thread and the nut badly damaged from dry firing on old BSA's. The rod could have been shortened to remove a squished section. That amount of space probably does't hurt anything. If you think it's going to be an issue fill it in with epoxy.
Click to expand...
After thinking about this I think I would attempt to tighten the nut down further. Others I see are not flush but sunk below the face of the leather about .050 or so. I've often been able to turn nuts like that with a good (Milbar) 90 degree snap ring pliers.

Borrowed picture
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KWK said:
After thinking about this I think I would attempt to tighten the nut down further. Others I see are not flush but sunk below the face of the leather about .050 or so. I've often been able to turn nuts like that with a good (Milbar) 90 degree snap ring pliers.

Borrowed picture
View attachment 511183
Click to expand...
Is there a taper built into that center piece for seal sizing?
 
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Gents, I appreciate your continued input on this! You bring up some interesting points, but it appears to me:

+ The latch rod is in as far as it will go - plus, it's anchored by a hefty pin that goes completely across the piston body.
+ The seal is likewise socked down as far as possible. I was able to turn the nut "out" a bit, but it won't go "in" any farther than where it started.

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In spite of this gun's age (built 1980!), to the best of my knowledge what you see is unaltered factory work. I got it in 1988, from a batch of new guns damaged by a flood in a retail shop (stock finish was a mess but metal fine). It was owned for decades by a friend of mine who probably never put 1000 rounds through it. And he's not an "airgun guy" at all - I'm the only one who's ever poked around inside it, and only to fool with lubes and swapping mainsprings. I'm a bit amazed at how new the guts look.
 
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