How do I adjust gas cylinder for SVT 40

Discussion in 'Curio & Relics Forum' started by pzettek, May 23, 2009.

  1. pzettek

    pzettek New Member

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    I just purchased an SVT 40.. I have the same problem many others have with shells not extracting correctly. I want to adjust the gas chamber, but it's not the "nut" is not moving. I noticed what appears to be a pin or something below it. Is this part of the adjustment? Is it a locking pin or something? If so, how is it suppose to move?

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  2. gdmoody

    gdmoody Moderator Supporting Member

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  3. Helix_FR

    Helix_FR New Member

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    though my experience with the svt 40 is also limited I know that the pin that you see is not right and may be the cause of your problem. The gas valves only require a gas valve adjustment tool. Pliers for removing a pin is not a requirement. That valve may be pitted and the pin is in there to keep it stable.
    Unfortunatly there is not a whole lot of info about these guns.
  4. TRAP55

    TRAP55 New Member

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    Before you even get started on the adjustment, the gas system and the chamber have to be spotless.
    The SVT has a fluted chamber neck to compress the case neck and aid in extraction. If it's not clean, the bolt will rip the case in half, and eventually break the extractor. Parts for these rifles are not easy to find.
    The gas adjustment nut is held in place by the gas piston. The gas cylinder covers the piston and drives the bolt actuating rod back.
    Corrosive ammo that was used in these guns causes havoc on these two critical parts. Piston and cylinder need to be cleaned after every use. They also need to be within specs. I have a source for these parts made in stainless steel if you need them. New made recoil springs too.
    Adjustment:
    4 tools you'll need are a SVT gas adjustment wrench, a rubber mallet, a SKS sight adjuster, and a broken case extractor will keep your day from being ruined. The SKS tool works on the SVT sight, and will double as a stock crossbolt tool as well. On a side note, the SVT was designed to be loaded with Mosin stripper clips with the magazine in place.
    The gas adjustment nut has 5 flats with numbers stamped on them. The flat facing straight up, and lined up with the index mark, is the setting the rifle is shooting at.
    For any given ammo, start at the lowest setting of 1.1. If the bolt doesn't cycle and eject the spent case, set the butt of the rifle on the ground and use the rubber mallet on the bolt handle to eject it. Turn the setting up to the next flat, making sure it's lined up perfectly. It has holes that have to be lined up with the gas port in the muzzle extension and barrel.
    Repeat this procedure until the case ejects about 5 feet from you. Any more than that, and you risk damage to the rifle.
    Surplus ammo:
    Light ball works the best, brass cases feed the best. Copper washed cases may have some feeding issues with reproduction mags. Lacquer coated cases work well if you keep the rifle from over heating with rapid fire, and they get hot fast! The lacquer melts off the case and gums up the chamber and flutes. A bronze .45cal bore brush and carburetor cleaner from the breech end will clean the chamber out and give positive extraction.
    This gas adjustment tool fits better than an original, and a fraction of the price. http://www.blackrivergunsmithing.com $14.95 delivered.

    That's the muzzle extension wedge that holds the muzzle extension to the barrel. Don't remove it unless absolutely necessary!
    Last edited: May 24, 2009
  5. pzettek

    pzettek New Member

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    Hey, thanks for your comments. I see now that the pin in question does not effect the gas adjustment. I'll wait for my tool in the mail and see what I can do to get it moving.. Thanks very much.
  6. TRAP55

    TRAP55 New Member

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    Post some pics of both sides of your rifle, and some clear closeups of the receiver stamps and I can give you some info and history on it.
    Almost forgot to add that the extension wedge "can" affect gas adjustment. The gas porting goes through a hole in the center of that wedge. If the wedge is off center it restricts the gas pressure.
    Last edited: May 24, 2009
  7. pzettek

    pzettek New Member

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    Hey thanks for the info. I was able to adjust the gas cylinder once I got the right tool. It made a huge difference. Now the gun fires correctly. Although I found another problem. It seems the sear pin may have some issues. Every few times I fire the gun, it sets off two rounds instead of one. I have it at a shop now to look at it.

    I'll post a few pics of my rifle here.

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  8. pzettek

    pzettek New Member

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    Sorry.. need to get another pic of the reciever stamps.
    Last edited: Jun 12, 2009
  9. TRAP55

    TRAP55 New Member

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    Close up of the top and both sides of the receiver, left side stock by the trigger.
  10. ncbelly

    ncbelly New Member

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    This is a nice looking rifle! It's the first that I've seen. I know of it, just never seen one.
  11. TRAP55

    TRAP55 New Member

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    ncbelly, never shoot one............cause then you'll have to own one!:D
    Power and accuracy of a Mosin, and recoil of a SKS. In fact, I think my SKS is harder to get back on target than the SVT is. It's good for clearing out both sides of you at the range too, the muzzle blast from the brake is horrendous!:eek:
  12. ncbelly

    ncbelly New Member

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    I still haven't felt the power of my Mosin yet. I haven't had it very long, but I can't wait to get it to the range. I would love to get an SKS also. I'm just getting into these older guns... My interest is growing more and more every day.
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