Weihrauch HW90 early version vs late version?

[gk10]

Hi All,
l have recently purchased an early HW90 in .177cal which according to the serial numbers database was built in 1993.
It has shown to be extremely accurate but unfortunately it has a slow leak. l acquired the parts to pump it up and l got it shooting nicley with 10.3gr Barracuda's at around 820 ft/s but then it lost power after a few days.
l have ordered a heap of parts to rebuild it from Chambers, including a new .22 cal carbine length barrel. I'm located in Australia so it's already considered a firearm so l might as well make the most of the power potential.
l was looking at other parts l may need and l noticed that the early versions have a different dummy piston.
The thread that the Schrader valve screws in has seen better days and l'm not sure if it will need to be replaced, however it appears that none of the places l've looked at has the early dummy pistons in stock.
Does anyone know what the difference between the early versions and the new versions of the dummy piston are?
Is it possible to modify a late dummy piston to fit?
Are there any other differences between early and late HW90's?
Regards
George

[Shed tuner]

trigger guards with integral safety reset button are different, but sorry, I can't help with the other queries.

[Weasle]

trigger guards with integral safety reset button are different, but sorry, I can't help with the other queries.

John

I don't want to Hijack this thread...However.... does the Trigger guard come away from the Action / Stock with no restriction, once the retaining screws are free?

Cheers Steve

[Shed tuner]

John

I don't want to Hijack this thread...However.... does the Trigger guard come away from the Action / Stock with no restriction, once the retaining screws are free?

Cheers Steve

yes....

[Weasle]

yes....

Many thanks

Steve

[gk10]

John

I don't want to Hijack this thread...However.... does the Trigger guard come away from the Action / Stock with no restriction, once the retaining screws are free?

Cheers Steve

On my gun l had to fiddle with the saftey and the trigger to get the trigger guard off. lt caused a bit of stress until l found an online disassembly guide that made mention to this.
l also noticed that mine does not have the small lock screw on the main trigger guard/action screw.

[Weasle]

On my gun l had to fiddle with the saftey and the trigger to get the trigger guard off. lt caused a bit of stress until l found an online disassembly guide that made mention to this.
l also noticed that mine does not have the small lock screw on the main trigger guard/action screw.

Hi George

Its seems as if mines the same...even down to the missing lock screw - I shall revisit the removal later.

The only reason to remove the guard is to gain better access to the adjustment screw running down thru the trigger blade. I understand that backing this off will give me a 2nd stage, something the trigger is missing at the moment.

Cheers Steve

[gk10]

Hi Steve,
l haven't fiddled with my trigger adjustment yet as it pretty good, however l can confirm that it does have a second stage.
Removing the trigger isn't really that bad, you just need to be aware that you can't force it in or out - nothing falls out.
Cheers
George

[peddy]

Hi All,
l have recently purchased an early HW90 in .177cal which according to the serial numbers database was built in 1993.
It has shown to be extremely accurate but unfortunately it has a slow leak. l acquired the parts to pump it up and l got it shooting nicley with 10.3gr Barracuda's at around 820 ft/s but then it lost power after a few days.
l have ordered a heap of parts to rebuild it from Chambers, including a new .22 cal carbine length barrel. I'm located in Australia so it's already considered a firearm so l might as well make the most of the power potential.
l was looking at other parts l may need and l noticed that the early versions have a different dummy piston.
The thread that the Schrader valve screws in has seen better days and l'm not sure if it will need to be replaced, however it appears that none of the places l've looked at has the early dummy pistons in stock.
Does anyone know what the difference between the early versions and the new versions of the dummy piston are?
Is it possible to modify a late dummy piston to fit?
Are there any other differences between early and late HW90's?
Regards
George

Different dummies pistons is news to me, I own a couple of 90s both many years apart but same piston. Why would you want to change the piston anyway? I bought both of mine as leaking. They are very easy to reseal. Was there air behind the shrader valve screw cap when you removed it? Sure sign the valve is knackered.

[bighit]

Different dummies pistons is news to me, I own a couple of 90s both many years apart but same piston. Why would you want to change the piston anyway? I bought both of mine as leaking. They are very easy to reseal. Was there air behind the shrader valve screw cap when you removed it? Sure sign the valve is knackered.

Looked on Knibbs site

Product Information

HW90 Dummy Piston

Length 135.5mm
O.D. of large end: 29.5mm
O.D. of small end: 23mm


Fits Models Post Serial Number 1710332

New Style


http://www.airgunspares.com/store/pr....-HW90DUMPIST/


Product Information

HW90 Dummy Piston Early

Fits Models Pre Serial Number 1710332

Length: 135.5mm
O.D. at Rear: 29.5mm
O.D. at Front: 23mm

http://www.airgunspares.com/store/pr...0DUMMYPISTONE/


From Chambers website

P116
Cyl End - Dummy Piston - Pre Serial Number 1710332
Price: No Longer Available
Cyl End - Dummy Piston - From S/N from 1710332 P116N
Cyl End - Dummy Piston - From Serial number 1710332



Could it to be do with the valve thread pitch ? Im sure Theoben also had two different threads on their dummy pistons and you had to buy the correct valve or it did not fit.

[Shed tuner]

if the smaller OD is the same, are they interchangeable ?

[bighit]

if the smaller OD is the same, are they interchangeable ?

Possibly . only weihrauch would know for sure .

[gk10]

Based on a few pictures on the internet, l now believe that the main pistons are all the same however difference between the new and old dummy pistons is the way they attach to the rear of the main cylinder.
Basically it looks like the early versions have a central set screw that holds the main pin, while the newer versions have an offset (lower) grub screw that locks the main pin.
lnterestingly there is still some sort of central part cavity/hole in the centre of the new dummy pistons (ie where the old set screw is situated) but l have no idea what (if anything this does).

Can someone who has a late version gun confirm what the central cavity does? ls it threaded or is it just a shallow indentation.

The reason l want to know is that l may need to replace my dummy piston as mine shows a bit of wear on both the sealing surface and the thread for the shrader valve isn't perfect so l may need to replace it.
l just replaced the schrader valve and re-pumped it but l don't now if it holds air just yet. lf it still leaks then l'll replace the o-rings and see how l go.

lf it still leaks, l'll need to replace the dummy piston but l can't find anyone that stocks the early ones.

Plan B is to buy a new version dummy piston and see if l can adapt it to fit.

l really like my HW90 and l can see that it has the potential to be an excellent break barrel air rifle (very accurate and powerful but really smooth) so hopefully l can repair it.

lf anyone has or knows where to source an early dummy piston, please let me know.

Cheers
George

[peddy]

Both of mine have a grub scew so must be later ones, you never stop learning with airguns. Was there air escaping when you undid the shrader valve screw end cap? A teaspoon of motor oil inside the piston helps keep things lubricated. Also I'd remove the inertia weight.

[gk10]

Hi Peddy,
l didn't notice any air pressure behind the valve, but l'll check again today.
When you checked your guns did you happen to see what the central hole/indentation does? ls it threaded?

Cheers
George