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SMK QB/XS/TH 78/79 Modified Exhaust Valve
£16.95 inc. tax
Material of Head*
SMK QB/XS/TH 78/79 Modified Exhaust Valve Summary

SMK QB/XS/TH 78/79 Modified Exhaust Valve

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Our Modified Exhaust Valve designed for more power, for the SMK QB/XS/TH 78/79 models. Ours have a Stainless Steel shaft rather than the standard mild steel one. 

        Our exhaust valve will unscrew so you can change the seal. Unlike the standard one which is just pressed together. The first picture is our Modified Exhaust valve with a Stainless Steel Shaft and tapered brass head, while the second picture is the standard exhaust valve with a mild steel shaft and barrel head. The last picture is our valves undone for seal replacement.


When fitting the seal to our valve, just unscrew the shaft from the brass head, then pick out the seal. Push in the new seal with the larger hole facing outwards and the smooth side facing outwards, then put a tiny amount of Locktite on the threads of the shaft and screw in the shaft until it is level. Do not over tighten so it is distorting or pulling the seal inwards. Just look from the side to see that the seal is flat across but with no gap behind the flange. If you have trouble holding the stainless steel shaft then it can be held in a drill chuck, and wet and dry can be used to give a grip on the brass head. 

If you have the special tool for removing the Piercer Body on the QB or XS 78, it will allow you yo remove the piercer body easier without damaging the piercer body because it fits the slotted groove exactly. After you remove the piercer body, it is then easy to remove the exhaust valve, spring and piercer even without removing the stock. 

If you are removing the piercer and valve etc with the gun still in the stock, there is a certain procedure to follow:

Make sure the gun is empty of Co2 and is not loaded. 

Remove the front cap and tip out any bottles (if any) to gain access to the piercer body. Place the tool down into the reservoir until it engages in the wide slot of the piercer body. Pressing firmly down unscrew the body anti clock wise five turns or until it disengages the brass valve body.


Tilt forward with your cupped hand at the front, until the piercer body, valve and spring fall out the front of the reservoir into your hand. If the valve has not fallen out then cock the gun, push the valve back into its brass seat, then hold the gun horizontal, then when you pull the trigger the hammer will knock the valve out into your hand. Be ready to catch it so you do not drop it.


Check the valve seat is clean and clear from debris, and also the valve face. If the gun has been leaking out into the barrel then replace the valve (if it is our one you can change just the seal), the standard valve seal cannot be replaced because it is pressed together.


Problem with leaking valves:


If your exhaust valve is not lasting very long (this is very rare with our valve) then you might have a damaged valve face this is easily cured by polishing the raised sealing seat of the valve body or simply changing the body.


Now the important bit: When you want to replace the exhaust valve, DO NOT DROP IT BACK IN, but hold the gun horizontal and place the valve in the front, tilt the gun up a little at a time until the valve gradually drops back to the brass valve seat without dropping onto the seal face (because it would dent it and cause a leak even with a new seal). Look down and wiggle the reservoir until the valve drops into the valve hole and seat. Place the valve, spring and piercer into my piercer body and holding the gun horizontal place it into the front of the reservoir. The place the special tool in the front and gradually push to the rear until it touches the brass valve body. You can then keep the pressure on to engage the brass thread and tighten the piercer body.


Then replace the front cap or put one empty Co2 bottle in and then a live one to test for leaks. You will obviously only get half the shots with one bottle.

Always check the power to make sure the gun does not exceed your limit, after changing any parts, especially if it is hot.

T R Robb
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