HW90 Gas ram Removal



Information below shows how to remove the gas ram from the Weihrauch HW90 air rifle.

The strip was performed on a UK spec 12ft/lbs version that was out of warranty, if you attempt the strip below on a gun that is still under warranty you WILL void all warranty’s that came with your rifle.

All the information below has nothing to do with the Weihrauch or Theoben  Company; the strip was produced by an air rifle enthusiast and not a qualified gunsmith.

by Following the instructions below you do so at your own risk. ?



Tools needed for the job:

Flat screwdrivers (Different sizes)

1 x 2.5mm Allen key

1 x Flat bottom object (Pin punch)

1 x Theoben gas ram pump

1 x Chronoscope

1 x Hammer


First start by removing the front stock screws using the correct size screwdriver.



Once you have removed the front stock screws turn your attention to the trigger guard.

You will see three screws of different sizes, start by removing the smallest screw located at the front of the trigger guard, this is a locking screw that holds the big screw next to it in place.



Before removing the bigger screw it would be a good idea to put a mark on the screw head and trigger guard, so that when you put it back you know exactly how far to turn it to get it back to the same position.

Now remove the big screw and split washer underneath it, then remove the last screw from the rear of the trigger guard.

You should now be able to pull the trigger guard away from the action, and remove the stock from the action.

Next look at the rear of the action, remove the screw and o-ring underneath it to gain access to the air valve as in the picture below.

(Ignore the locking grub screw for now)



Once you have the screw out of the way you can now start to let the air out from the ram by tapping gently on flat bottomed object positioned on the valve pin.

(See picture below)



Now all the air is expelled from the ram, you can remove the trigger unit and cocking arm.

To remove the trigger unit simply drive out the pin pictured below (use a pin punch) then just pull out the trigger unit from the action.



Drive out the pin from the cocking arm that is in the bottom of the breech block, shown in the next picture.



Once the pin is out you can pull the cocking link/arm out towards the barrel until the other end of the cocking link reaches the opening in the cylinder.

When it reaches this point you can remove it from the gun (see picture below)



Next you need to remove the large pin at the rear of the action, but before you can do this you MUST first remove the small locking grub screw on the back part of the ram next to the valve area  with a 2.5mm allen key. (see picture below)

Note: the trigger unit is still in place in the pictures but should be removed, pictures were used from an earlier stage.




Then you can remove the large pin that goes through the cylinder and rear of the ram as in the next picture.

Use a pin punch and hammer to remove the pin.



When you have the large pin out, push the piston/ram out of the cylinder via the cocking slot under the cylinder.

This way it should come out in one piece, as pulling on the rear of the ram would only remove the valve body and not the piston.

The next picture shows the ram coming out of the rear of the action.



Now you should have the complete ram removed from the gun (pictured below)



The ram can now be pulled into two pieces to expose the inner part of the piston.



Looking inside the piston you can now see the o-ring/seals. (pictured below)


Now you can service your gun as required, be it a simple piston seal change or a complete degrease and re lube.

When you have completed your work put the gun back together in the reverse order as you took it to pieces, until you need to refit the trigger guard then follow the directions below.

To refit the trigger guard you must first cock the trigger unit, to do this you need to pull the foot shaped part towards the barrel end of the gun using a screwdriver until you here a click and the part stays at its new location.

The pictures below show you the part that needs to be set first in order to refit the trigger guard.

The first two pictures just show the trigger unit on its own so you can see more clearly the part that needs setting.





The next two pictures show the same part, but with the stock now on the action as yours would be.




Once you have set the trigger unit you can now refit the trigger guard by holding down the safety off button on the side of the guard while fitting the guard back on the gun.



If your trigger guards feels like it won’t go back on you may need to pull the trigger blade about 1 or 2mm just enough so that it clears itself away from the gap in the trigger guard housing.

Only pull the blade slightly as stated above otherwise you will release the foot shaped part and then trap it under the trigger guard in the wrong position.

When the guard is back in its normal position replace all the screws you removed at the start of the strip.

You gun should now be back in one piece and working as good as new.



Stripdown provided by Airgunforum.co.uk