Umarex Desert Eagle Rebuild

Once I was close to the 8mm outside diameter, I began boring out the main central gas way while the bulk of the material was still in place to soak up some of the heat, and maintain structural integrity during drilling.



Needed to be very gentle here, and quite accurate with the depth to make sure it would meet up with the two angled ports when they were drilled.

Once completed, I moved back onto the outside form.







At this point I am beginning to form the shape of the back end of the valve core, which means the part needs to come out of the chuck and be flipped round to continue the back end features. This is quite tricky, particularly on a cheap Chinese lathe, as trying to get the reversed part concentric with itself is very important, and any misalignment is particularly noticeable on small parts.

More to follow...

Superb work so far mate, what a talent. Can't wait to see the results

The drilling didn't go so well, I broke four drills and wore out three diamond coated Dremel tools producing these holes, my grip wasn't firm enough either and I buggered up the seal edge in the process. 😭



But in the end, I finally defeated the stainless steel and was able to re-cut the seal edge and file the flat onto the rear spigot. Again, no milling machine, but I like to think that I am reasonably good with the needle files.



My guess is that the flat is to allow some gas backwards to operate the blowback.

Here are the old and new parts, the largest outside diameter is 8mm,the two co2 holes are 2mm.




After a bit of head scratching, I was able to get the pistol back together, new seals in the valve, and the moment of truth - tightening the plug to pierce the co2 capsule...

More to follow...

Very well done Mark. A great read as well sitting here in Costco waiting for new tyres to be fitted. Love the suit.

What a superb read! Well done, I think that’s a very impressive repair

I am free!

So here is the area in question that is the root of the full-auto slide effect.



In this image the slide is removed and the mechanism partially pulled out from the grip. There is a a short bar with a lug in the middle, and a longer link bar between the trigger and the hammer.
The principle of operation is as follows. When the trigger is pulled and the hammer strikes the valve, the slide is driven back very quickly, at this point the shooter will still have the trigger fully back, because the mechanism is much faster than the finger. To stop the full-auto effect, the long link bar needs to be momentarily disengaged from the sear. This is where the short bar with the lug comes into play. On the inside of the slide is a 'liner cam' that pushes the lug down as it moves backwards.



Hopefully the picture makes sense, there is an edge inside the slide with a dog-leg towards the right end, as viewed in the image.
The short bar is pushed down against the long link bar, disengaging it from the sear when the slide is at its rearmost position, keeping the hammer cocked.

Over time the alloy lug on the short bar gets worn away by the slide, so it doesn't press the long link bar down far enough to disengage from the sear.

Here is a closer look at the worn lug.



I decided that trying to build up anything robust enough on the lug was beyond my capabilities, so decided to give the long link some pre-engagement by adding a 0.5mm packer to the top edge.



In this picture you should be able to make out a black line on the top central portion of the long link. This is a piece of plastic card, superglued in place, scoring the alloy first to give it a key.
This has worked for me for now, once the alloy wears some more, I will have to revisit the problem!

Hope this helps, any questions, just ask. 😁