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PostPosted: Wed Jul 16, 2014 5:46 am 
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Joined: Wed Jul 16, 2014 5:10 am
Posts: 12
First of all hi, I am new here :)

I am new to this gun and not had one since I was 14. Can anyone provide information or a link on how to change a valve stem in this gun? Also when replacing with a different valve stem is it necessary to alter the hammer preload (i think that is what it is) where the long Allen key is used.
or is this just another adjustment that can be made and is not a requirement when fitting valve stem?
thanks in advance.

ps To moderators sorry if in wrong forum.


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PostPosted: Wed Jul 16, 2014 9:50 am 
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Found a video on youtube in what i think is Russian, but it gives me an idea, but any others hint or tips welcome.

I am still unsure whether or not I need to change the hammer spring preload??

Thanks


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PostPosted: Wed Jul 16, 2014 1:42 pm 
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Location: Central West River Nova Scotia
Adjusting the hammer preload is pretty much useless without a chrony. Changing the valve stem for more power is easy but still requires a chrony to see where your new pellet speed is. If its too high your accuracy will suffer. If you decide to go back to low power you will have to change it back. I would suggest a second tube/air reservoire, one low power and one high.
Oh and welcome to the forum.

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PostPosted: Thu Jul 17, 2014 12:58 am 
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Thanks for the tips and the welcome. From the video I gather the valve stem is in the brass fitting which screws into the air tube/cylinder. So once the air cylinder is removed and DEPRESSURIZED! it is a case of removing the white plastic/nylon piece and then the spring, take out the valve stem and fit new, put back together?

I can understand the chrono need if messing with the hammer preload as you don't know if you are improving performance or not, but fitting the valve stem will improve performance no matterwbat? Wont it?

I am not after super pinpoint accuracy like I have read about members filling holes in the valve etc. I just want more power, as after my homemade 12mm pneumatic QEV gun firing ball bearings anything is accurate, ifs just the 12FPE is kind of feeble after my homemade gun, it wasn't pretty but flipping hell was it powerful even on only about 130psi, one day accidentally filled to around 300psi, which I had previously not done. I was terrified something would blow but it didn't, wouldn't want to do regularly but it really put out some power.

I am not after super accuracy, if I can hit a tin can at 50M I will be happy.

just looked at chronographs on ebay, are ones like this OK or just junk?

http://www.ebay.co.uk/itm/291180895435?redirect=mobile


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PostPosted: Thu Jul 17, 2014 4:30 am 
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Sorry for extra post, I seem unable to go back and edit my previous, is this normal?


Ref the chronograph, I have seen pics of 2 types the small one like linked and then a larger one with like 2 sets of V shaped rods, I imagine this type is better/more accurate as it has further to measure the pellet or am I completely off?


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PostPosted: Thu Jul 17, 2014 6:26 am 
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Location: Central West River Nova Scotia
Changing the valve stem IS, just that easy. Removing the valve body from the tube, might not be. If you have not done it yet, heres a little trick. Heat the valve threads with a hair dryer or heat gun on low. Then with the proper size wrench on the valve and a tight grip on the tube, use something to sharply hit the wrench till the valve breaks free. Also carefully remove the plastic plug from the valve try not to damage it too much.
as for the chrony. That one on EBay works fine, but I found it a PIA to use, and even shot mine. Now it doesn't work. The one with the v shaped wires is deffinetly a better choice. Hitting a pop can at 50 yds should be a piece of cake for the at44.
might I ask,,, did you buy a PAL valve stem, or are you modifying your existing one ?

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PostPosted: Thu Jul 17, 2014 6:48 am 
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Thanks for the advice, does the white.plastic.thing just need wiggling and pulling or is it threaded?

Also how do you hold the cylinder.when undoing valve/brass assembly? Wrap it in a towel etc and clamp in a vice carefully? Is the brass assembly loctited or is it just done up tight against rubber o ring, when reassembling what do you torque it to? Or just nice and tight?

As for the valve stem I purchased a full power one from what I think is this sites shop, not sure if they are made by Hatsan or modified by Sniper?


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PostPosted: Thu Jul 17, 2014 9:42 am 
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Location: Alberta Canada
JMS wrote:
Thanks for the advice, does the white.plastic.thing just need wigglingJust wiggle carefully, while pulling out ward. and pulling or is it threaded?

Also how do you hold the cylinder.when undoing valve/brass assembly? Wrap it in a towel etc and clamp in a vice carefully?Leather or rubber works better than a towel. Just tighten enough not to spin. Overtightening can and will OBLONG the tube. Is the brass assembly loctited or is it just done up tight against rubber o ring, when reassembling what do you torque it to? Or just nice and tight?With bottle secured, once bottomed out against the oring just a light tap against the wrench is all that is required to set the torque. Be sure to lubricate the threads and oring. It will help when the next time comes to remove the valve.

As for the valve stem I purchased a full power one from what I think is this sites shop, not sure if they are made by HatsanMade by Hatsan or modified by Sniper?

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PostPosted: Thu Jul 17, 2014 11:51 am 
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Thanks for clarifying and the leather idea, is the grease used on flashlight o rings/threads ok to use?


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PostPosted: Thu Jul 17, 2014 7:57 pm 
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Location: Alberta Canada
Di electric greases are fine for nitrile and viton orings but will swell buna. Parker Oring lube Moly Kote or silicone grease from dive shops for orings.
Any type of grease upon threads just a small amount 3 or so threads in upon male end. That way you dont introduce it to the vessel interior.

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PostPosted: Thu Jul 17, 2014 8:17 pm 
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Location: P.G. B.C.
Don't lose the while plastic plug or a new one will cost over $5.00 - I know. I do wish the AT44's had a steel one, threaded, like the BT65's - much nicer.

There will be a spring under it as well, pushing on the 'stem' to seat it against the inner white plastic 'valve' inside the brass valve body.

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PostPosted: Sat Jul 19, 2014 11:28 am 
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Fitted new full power valve stem to UK spec 12fpe, but found that the valve stem end has a different profile to original, it is more pointed and protudes futher than original uk one. So when i go to fill the gun the air leaks straight out and the filler probe will not even seal as not enough pressure builds up. My uk spec stem seal is 2.62mm (0.103") on the stem.

any ideas on what i can do, I am really disappointed, was hoping for some more power.

sorry hope who ever doesn't mind me using the picture but my uk one looks like the top one of the 2 stems with more of a blunt end and almost identical diameter, so how do the restrict the uk ones would it be the hammer spring? Looking at the stems the UK model uses a stem virtually the same if not identical to the full power version. What else can have been altered? Help!!!


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Last edited by JMS on Sat Jul 19, 2014 11:56 am, edited 1 time in total.
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PostPosted: Sat Jul 19, 2014 11:52 am 
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Joined: Mon Sep 05, 2005 10:55 pm
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Location: Rocky Mtn Hse Alberta
JMS wrote:
Fitted new full power valve stem to UK spec 12fpe, but found that the valve stem end has a different profile to original, it is more pointed and protudes futher than original uk one. So when i go to fill the gun the air leaks straight out and the filler probe will not even seal as not enough pressure builds up. My uk spec stem seal is 2.62mm (0.103") on the stem.

any ideas on what i can do, I am really disappointed, was hoping for some more power.

sorry hope who ever doesn't mind me using the picture but my uk one looks like the top one of the 2 stems with more of a blunt end and almost identical diameter, so how do the restrict the uk ones would it be the hammer spring?


Forget to install the white plastic valve seat?
Order of parts? Body, seat, stem, spring then plastic plug.

Edit
Either clock hammer or fill with tube out of gun.

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PostPosted: Sat Jul 19, 2014 12:22 pm 
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Joined: Wed Jul 16, 2014 5:10 am
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When you say plastic white seat, what do you mean, I didn't see that part, hope i haven't lost it! I will try filling off gun, then at least i will know the valve is sealing, i will try right now.

just put in 100bar, slightly concerned what is going to happen when i fit to gun. Screwed cylinder in then it went tight about 2mm before the to faces mated, so i removed cylinder as. Didn't want to try tightening more as scared may cause damage to hammer or something else, think i will refit stock stem until I can find a solution. I will photo stock and full power valve stems once removed to show what I mean, didn't think to look before fitting.

Here are the two valve stems, they seem identical except for the tips.

All back to stock now :( looks like I am going to have to research alternative routes to more power.


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PostPosted: Sat Jul 19, 2014 6:12 pm 
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Just had a thought, when the side lever on the gun is docked I guess this pulls the hammer back, so if the cylinder was then fitted would the hammer open the valve more? Would this help flow, decrease it or just damage something?

As my valve stem is virtually identical to the one that gives your guns 30fpe or so I wonder if they shortened the UK stem to stop the hammer from opening the port as much? But would fitting the valve stem cause the valve to be open after the gun is fired and just loose all my air? Maybe the hammer or some other part is different on a UK gun, sorry just thinking out loud in the hope that someone who knows the gun may be able to help me, I am desperate for more power and disappointed the valve stem didn't work, thanks.

PS. Did just watch a video on YouTube titled "Tuning of ranger (Hatsan) AT44" and the guy replaced what I believe to be the valve spring with a new longer version, whether this is a Hatsan spring or custom I don't know.

I also read this, taken from an Australian forum,

Brooksey, 3.2mm is the uk spec transfer port diameter. Change that and remove 1 of the preload washers from the hammer spring and I think you will get the result you are after :) . If you back the hammer spring tension off too far then you will find your lock time will become very slow which is not conducive to accurate shooting. I've been messing around with my bt65 recently, fitted a regulator and made some other adjustments and the shot count has more than doubled and accuracy is as good as it ever was, and it is a whole hell of a lot quieter :) . Incidentally, your at44 would have been producing closer to 40 fpe in standard guise, my bt65 was producing 43fpe and my wife's at44 was at 41fpe when we first got them. At those energy levels iron sheeting doesn't stand a chance :( .

So it seems as though the UK guns have smaller transfer ports, another post said this -

I have had a rebel before and its what made me buy a pcp... I agree with your comments but the great thing about a pcp is it is both a low power and high power in one you just have to restrict air supply and shes a low power shooter... e.g the uk 12 fpe version is the "same" gun just less hammer strike, valve openings, thinner transfer port and I believe a thicker valve needle, I could buy another gun and in any other country I would but until aus stops stops being the anti's little bitch and derestricts air rifles this is the one for both pidgeons in the paddock and the shed

So it would seem I am kind of stuck on increasing power as I would imagine enlarging the transfer port is virtually impossible?


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