Keep Your UZI Running
The UZI is known as a tough, tireless workhorse that never fails. While thereís a lot of truth to that, it needs good care like any other firearm. Out of spec parts or poor maintenance can put your afternoon of fun on hold quickly. Here are some suggestions to consider the next time your workhorse stumbles. Most of these suggestions apply to fully automatic or semiautomatic UZIs but youíll find that replacement parts for the semiautomatic are harder to find and more expensive so thereís an incentive to repair rather than replace in that case. The three most common problems youíll run into are failure to fire, failure to eject and failure to feed.
Failure to Fire
|The UZI bolt face, showing unused firing pin (A) and the extractor claw (B) in the proper position. Note that the extractor rests on the raised rim just below the claw.|
A failure to fire occurs when the round is fed into the chamber but the primer doesnít detonate. Usually the round will have a light primer strike on it. There are three possible causes for this. First, the open bolt firing pin, which is a small projection milled into the bolt face, may be worn or broken. This is an uncommon cause but if it happens, the firing pin will need to be welded up or the bolt replaced. Surplus bolts are cheap and plentiful so replacement is usually the easiest option. The firing pin on the semiautomatic UZI is pinned to the carrier and can also be replaced if worn.
Another cause is excess headspace. If the round doesnít seat firmly in the chamber, the bolt will push the round forward rather than detonate the primer. Excess headspace can be caused by an out of spec chamber but thatís uncommon. A more likely cause is a loose barrel nut. This simple to diagnose, simple to fix problem can easily go unnoticed. With the barrel nut tightened you should not feel any play in the barrel. If the problem is chronic, it might be due to the barrel nut catch being worn or the teeth on the barrel nut being broken off. Either part can be easily replaced. Remember to depress the barrel nut catch when tightening the barrel nut to reduce wear on both parts. If the problem persists, an easy cure is to put a rubber or copper gasket between the barrel flange and the barrel nut. Another rare cause of excess headspace is broken trunion welds. If the welds that hold the trunion inside the receiver fail, the trunion will slide forward when firing the gun. Rewelding the trunion should be done by a qualified gunsmith.
The final cause of failure to fire occurs when the bolt moves forward so slowly that it doesnít hit the primer hard enough to detonate it. This is actually a type of failure to feed and will be discussed later in the article.
|Broken teeth on the barrel nut will allow the nut to loosen when the gun is fired.|
|If you can hear the clicks while tightening the barrel nut, then you are wearing out the front edge of the barrel nut catch. To avoid the problem, the barrel nut catch should be held down until the nut is tight. The catch on the left shows wear but the front edge is still square so itís serviceable.|
|The barrel trunion is welded to the receiver in two spots on each side. If the welds break, the trunion can slide forward as depicted in the right photo. The left photo shows the proper position of the trunion up against the front of the receiver.|
Failure to Eject
The point of the ejector (A) faces forward and strikes the base of the cartridge as the bolt recoils. The rivet head (B) can be seen to the side of the ejector.
Failure to eject is also known as stovepiping. The first possible cause of failure to eject is weak ammo. The heavy bolt and recoil spring of an UZI require a heavier impulse to operate than a typical 9mm pistol. UMC and Remington green box ammo are notoriously weak and can cause failures to eject. If the empty cases are not ejected several feet from the gun, try different ammo.
If ammo isnít the problem, take a look at the ejector. It should be level, tight and pointing straight forward. Itís riveted to the bottom of the receiver and if it gets loose it wonít firmly strike the back of the fired case as the bolt recoils reward. To tighten a loose ejector, remove the grip frame from the gun, exposing the bottom of the rivet. With the top cover and bolt removed, turn the gun over and rest the head of the rivet on a support, then hammer the bottom of the rivet until the ejector is tight. Once itís tight, install the bolt without the recoil spring and push the bolt forward and backward by hand. It should pass over the ejector without hitting it. Performing this check with the barrel and stock removed will give you a better view of the ejector clearance.
|To secure a loose ejector, turn the receiver upside down and support the rivet head. A bolt held in a vise makes a suitable support. Use a punch and hammer to peen the bottom of the rivet until the ejector is tight.|
If ejection problems persist, itís time to check the extractor, which is the leading cause of failures to eject. The extractor must firmly grip the case as the empty round strikes the ejector in order to generate the energy needed to flip the case out of the gun. Remove and clean the extractor, particularly under the claw. Residue buildup under the extractor claw will prevent it from firmly gripping the case rim. Also clean the bolt hole that the extractor sits in. A .22 caliber cleaning swab works nicely for this. Residue in the hole will prevent the extractor from flexing properly. Before reassembling, be sure that you have the correct extractor in the gun. 9mm extractors are unmarked while the .45ACP extractors are stamped ď45Ē near the back. They are not interchangeable. For best results itís also best not to mix up semiautomatic and fully automatic extractors. The lower point of the extractor claw is removed on the semiautomatic extractor to facilitate feeding. When everything is clean, reassemble by inserting the extractor through the back of the bolt. Line up the long slot on the back of the ejector with the arrow on the back of the bolt. Reinsert the extractor retaining pin from the left side of the bolt. Using a small screwdriver, try to push the extractor claw sideways. It should require firm pressure but move freely. If thereís no tension on it, the extractor will have to be removed again and bent slightly. If nothing else seems to help, replace the extractor.
|To remove the extractor, push the extractor retaining pin out and then push the extractor out from the front side of the bolt.|
The semiautomatic extractor (left) has one corner of the claw
removed. This ensures reliable feeding as the case rim slides up the
bolt face. Cases do not slide up the bolt face on fully automatic bolts
because the lower lip of the bolt lifts the case rim over the extractor.
The rim snaps under the extractor as the bolt closes.
The .45ACP extractor (top) is stamped ď45Ē. 9mm extractors are
Failure to Feed
Failure to feed is the most difficult problem to diagnose because there are many potential causes. A failure to feed occurs when the bolt cannot forcefully strip the round from the magazine and push it into the barrel chamber. The problems fall into three categories: bad recoil spring, excess friction on the bolt, or misalignment of the gunís components.
A weak recoil spring wonít impart enough energy on the bolt for it to feed a round properly. Recoil springs can get weak with use and itís good to have a spare on hand, but itís not a common problem. A more common cause of a spring related failure is aftermarket springs that donít meet factory specs. Surplus IMI springs are cheap and plentiful so you should replace it at any sign of problems. The entire spring and recoil rod assembly should be replaced as a single piece.
A much more common cause of failure to feed is excess friction on the bolt and that can come from several sources. The first thing to check is the gap between the bolt and the top cover. Use a feeler gauge (available at automotive shops) to measure the gap. It should be between .005 inches and .015 inches; preferable about .010 inches. If the gap is too small, the top cover will need to be bent to give more clearance. You donít need any fancy equipment to bend a top cover; just a little patience and ordinary hand tools. The easiest approach is to flip the top cover upside down and support both ends with blocks of wood. Use a rubber mallet to hammer the middle of the top cover to put a little bow in it. Do it slowly and re-measure the gap frequently. If the gap is tight towards the front or back of the bolt, bend the front or back of the top cover down. You can get by with a vise and a crescent wrench to bend the ends of the top cover. Be sure the gap between the bolt and top cover does not get excessively wide because it will allow the bolt to slide past the sear without depressing the trigger. That would cause a ďrunawayĒ condition and can be extremely dangerous.
|Insert a .005 inch feeler gauge between the bolt and top cover. If it does not move freely, the cover will need to be bent to reduce friction on the bolt. A .015 incher feeler gauge should be tight to avoid a runaway condition. Check the gap with the gauge inserted straight in, pointed backwards, and pointed forwards.|
|The long slot on the back of the extractor will be horizontal when properly reinserted in the back of the bolt. Fully automatic open bolts will have an arrow showing the proper alignment.|
If the top cover gap is okay, verify there are no other sources of friction by using the bolt slide test. This test only works on open bolt UZIs. Assemble the unloaded gun without the recoil spring, remove the magazine, put the selector on full auto and hold down the grip safety. While pulling the trigger, tip the gun forward then backward. You should hear the bolt slide freely from the front to the back of the receiver. If itís binding anywhere youíll need to find where itís rubbing and correct the problem. One common cause of binding is trying to use surplus machine gun bolts in a converted semiautomatic UZI that still has a barrel restrictor ring. An IMI machine gun bolt will not have enough clearance and will rub on the top of the restrictor ring. If thatís the problem, the best solution is to have a qualified gunsmith cut off the top of the restrictor ring, leaving just the machined feed ramp.
If friction isnít an issue, then the problem may be due to misalignment of the gunís components. First check the magazine. Bent or cracked feed lips will cause misfeeds so the easiest test is to try different magazines. The original 25 round IMI magazines are the most reliable for function tests. Another magazine related problem occurs if itís held too high in the magazine-well. To test for this youíll need to repeat the bolt slide test mentioned above, but do it with a magazine body inserted in the gun. You must remove the magazine spring and follower for the test to work. If the bolt rubs on the feed lips during this test, youíll need remove the magazine catch and bend it so the magazine is held in a lower position. Check several magazines before bending.
If the magazine alignment looks okay, the other potential alignment problem is much more serious. When the barrel is not properly aligned with the bolt, the round being fed into the chamber will not feed straight in, resulting in a light primer strike or the round jamming between the bolt and barrel. This type of alignment problem is most commonly found on guns built from Group Industries receivers (original Group Industries or Vector guns) due to those receivers being somewhat out of spec. Additionally, the heat treating done by both Group Industries and Vector warp the receivers and they need to be straightened before assembly, occasionally resulting in misalignment. Straightening a misaligned receiver is not something you should attempt yourself so if everything else checks out on your gun and youíre still experiencing failures to feed, the best alternative is to contact Vector Arms for their recommendation on factory repairs. Vector will do repair work on any brand of UZI and their customer service is first rate.The simplicity of the UZI design will allow you to diagnose and correct most problems easily should any arise. With a minimal amount of care, this legendary submachine gun will give you a lifetime of reliable operation.
Originally published in the January, 2008 issue of Small Arms Review Magazine.
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Last Modified: May 27, 2017