Hw75 help

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springer_shooter

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Hiya I'm trying to find some info on the hw75, mine seems to of lost power over time and pellets now struggling to punch clean holes in paper targets, check over the chrono show its doing between 1.3ft lbs and 1.6fts, with the guns unusual preffered r10 (7gr) pellets.
so something is wrong somewhere.
The breech seal looks fine and so I'm suspecting it's something else causing the low power.
Has anyone got any tips or likely causes or any advice on fixing before I just fire the parts cannon and order all the seals and o rings available on chambers website? Ie is there one that's a known problem or wears out quicker etc?
Any advice appreciated
 
MrLuftArtisan said:
Make sure you put something in to pin/hold the trigger group in place before removing the cylinder 😁
Click to expand...
How's best to do this? I remember on my hw 45 there's a a small hole you put a paper clip through in the pistol grip but I've not looked at stripping the hw75 yet but think it'll be needed as the pelgun oil applied as mentioned above didn't fix things
 
On the 75 you don’t need to touch the trigger - 2 pins takes the whole compression unit and rear chamber out
 
You could probably get away servicing all the seals just by removing the one pin highlighted - I did when I cleaned out my valve of old gunk
IMG_1098.webp
 
springer_shooter said:
How's best to do this? I remember on my hw 45 there's a a small hole you put a paper clip through in the pistol grip but I've not looked at stripping the hw75 yet but think it'll be needed as the pelgun oil applied as mentioned above didn't fix things
Click to expand...
Can you hear air escaping when you close and compress?
 
Fully opening is the air rushing in - this is normal

When closing if you hear air it can sometimes be the valve seal

If you have no pressure closing I would replace the piston o ring 2158 and tube o ring first 2158 also

Does yours have the felt pad on the piston? Newer ones don’t - when fully open you’ll see it - make sure this is wet
 
Reevo17 said:
Fully opening is the air rushing in - this is normal

When closing if you hear air it can sometimes be the valve seal

If you have no pressure closing I would replace the piston o ring 2158 and tube o ring first 2158 also

Does yours have the felt pad on the piston? Newer ones don’t - when fully open you’ll see it - make sure this is wet
Click to expand...
I'm not sure as I haven't stripped it down yet as one of the earlier posts put me off by mentioning the need to pin the trigger assembly in place? I've rebuilt my hw45 before and had to pin the trigger assembly in place, is it the same on the hw75?
I'm thinking the cause can only be the piston o ring or the main valve seal but wanted to be totally confident about the trigger before I strip it down.
 
Definitely don’t need to touch the trigger as the hammer knocks the valve open

The hw45 trigger sears hold back the piston so are different

Literally that one pin
 
I've gone to strip the gun this weekend but can't see how you're supposed to remove the pivot pin at the rear? It has what looks to be a rolled edge/lip and trying to drift this out looks like it'll likely damage the pin/frame of the pistol.
Does anyone have any ideas about this? I've attached a pic to show what I mean, it looks like a pin with a tiny circlip but on closer inspection it's all one part , no removable clip?
 

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Cheers, you was correct, it was the most fiddly clip I've encountered but it's now removed.
I've just removed the cylinder and valve assembly and I've been greeted by two areas which both look non original? I'm thinking someone must of had an attempt at working on this pistol before me?
The pistol is second hand purchased a few years back so I'm wondering what's going on here? One galv flat head that looks potentially non original and some kind of sealant/silicone applied at other end?
 

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Make sure that felt washer is oiled

Check for any nicks or caught areas
 
Does anyone know if the white stuff on outside of cylinder is something applied at factory or possibly a bodge repair of something by previous owner?
 
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