the adjustable external hopup sounds the go … would look good as an extension if you can ream out the outer sufficiently.
1 Like
ill send mine back to you for some R&D? 
I know your busy though …
1 Like
Hold onto it for now, it will just sit here for around 2-3 weeks at the moment… I have suspended taking on jobs for the next couple weeks so I can catch up on the jobs I already have… and get some of the new blasters ready.
Would be good to look into one and find out. @Friendly_Fire is definitely gonna beat me to it!
I had always decided mine was in the second batch, I knew they were all going to disappear quick.
Being AEP I suspect they will be a bit limited to what they are capable of, but I am sure some improvement can be done.
2 Likes
You are most welcome and the plan comes together thanks to @RokSolid and @BME .
Gotchya again 
Thanks for the call, hilarious. You deserve a treat now and then for your community support, knowledge, skills are amazing and makes for great reading for me.
I’ve seen you give away blasters for free. Hold up what’s this guy got, nothing. I’m going to change that situation. 
You may well see me give away a few more very soon. 
It was fun to pay it forward and help out some of the peeps on here.
Also made room for more blasters and guitars! 
Biggest regret is that I can’t ship one over to you @Maiphut because of your state’s ownership restrictions. 
1 Like
Yea bit of a bummer about that. But it is what it is. Thought about it for few weeks I’d like one of those APC9 then, hang on I can’t fit more in but nothing stopping me from partly funding what you deserve. Mum’s the word haha
I would of like to have seen the look on your face, wtf is going on here. Merry Christmas haha
1 Like
Good things happen in 3’s…
Thats the last of it…
For now…!!
Time to pull this gearbox again and get stuck into it.
A pre-test with fresh gels returned a resut of around 170FPS.
Yanking that puppy out took five minutes this morning… amazing how easy it is when you’ve been there, done that.
Gearbox Tear Down
First thing, get all the wiring out of the way. ZY use hot melt glue to keep everything neat… ugh! 
Pick that off.
Next step is to free the mag prime switch, one screw out.
Using longnose pliers, very carefully pull the mag terminals free, taking not of their orientation. A word of warning, they were very tight.
With those components free the wiring loom can be freed from the receiver and pulled out of the way… note the priming switch and positive terminal are separate.
Remove the tappet return spring.
Remove the screws from the front of the receiver and pull out the inner barrel. Note that the inner barrel is in a sleeve which locates in the t piece with a detent moulding Gen 8 style. This can be removed and the barrel shortened at the t piece end. There is a moulded detent in the 9.5mm bore of the t piece collar, so a flat will have to be filed on the inner barrel end to allow it to slide into the collar.
Note also that the diameter of the aperture of receiver where the inner barrel exits is NOT 9.5mm, it’s about 9.0mm. It fits the standard barrel with the machined groove fine, but that hole needs to be opened out to 9.5mm to allow closure of the gearbox shell halves with the shortened barrel 9.5mm diameter.
Remove the rest of the receiver screws and carefully pry the clamshell apart, keeping an eye on the piston spring as you go. There is no quick release on the spring but fortunately the spring retainer keys into the box shell on both sides of the receiver shell, so it’s not likely to go boing on disassembly.
With the box separated, the motor can be pulled out leaving a metal geared clean gearbox with no wiring to get in the way. Interesting that the motor gear isn’t bevelled but a straight cut brass or bronze gear, pretty standard for an AEP.
All the internal components laid out
The nylon piston has a full metal rack, albeit tiny. One tooth removed on the pickup side, a fairly standard nylon piston head and, surprisingly, what appears to be a decent green o ring.
The cylinder is alloy and has an inside bore of 20mm. Length is 45mm, but swept volume would be more like 40mm, so not much volume to work with. The nylon cylinder head appears to be permanent in the cylinder and can’t be removed, the spigot diameter for the nozzle measures 5.3mm, the nozzle is proprietry with a moulded lug that locates in the tappet plate.
The piston spring has a wire diameter of about 0.9mm, is 95mm in length unsprung and has a coil rate of about 5 coils per inch in the old scale. Outside diameter is about 10mm, the retainer will accept a spring with an I.D. of no less than 7.0mm, the piston itself will accept a spring with an O.D. no larger than about 11.0mm.
The main drive gear ( it ain’t really a bevel gear ) is cast iron with very small teeth to engage the motor, so big spring upgrades are pretty much out. It’s runs on ball bearings in the shell, and was noticeably tight to pull out.
The crown gear, sector gear and AR latch are all cast iron and fairly chunky, running on solid bushes. The weak point in the gearchain is definitely the gear above.
Possible Upgrades
Compression is surprisingly good, but with a bit of a normal loss of compression with the nozzle at full extension. About all that can be done there is liberal grease on reassembly to maybe improve airseal at the nozzle.
Fitted a short spacer (10mm in length) behind the piston spring to beef up compression slightly, but given the weak drive gear, nothing too wild. A 10mm long length of 9.5mm inner barrel was used, but keep in mind that preloading the spring does make reassembly a little trickier with no “quick change” feature.
Time to regrease, reassemble and test.
I’ll call that a good result for such a small unit… tested with AKAs to show an overall gain of roughly 60FPS from stock trim, about a 70% increase in power.
Conclusions
Not very upgradeable but possible. Reducing the stock 25cm barrel length down by about 8cm helps with the VE, but still not optimal. No doubt shortening more would help, but the design is such that if you shorten too much the inner barrel is unsupported in the receiver. Might be able to look at shortening more down the track and using a hop up to locate in the outer barrel for support.
Proprietry design means no readily available upgrade parts. The stock spring can be beefed up with a 10mm spacer, seems to increase FPS by about 20-25FPS and the small 370 motor seems to handle it okay.
Not the easiest blaster to work on, but definitely not the hardest either. Most of the difficulty comes from actually getting the gearbox out of the receiver and getting the box mounting screws back in. Not impossible, just a bit awkward with the motor wires running down the side of the gearbox.
So all up for this unit…
Stock trim. : 140FPS
Shortened I.B. : 170FPS
Spring Spacer : 200FPS
As this blaster started out at 140FPS, I guess it’d be fair to assume that a unit with a baseline FPS of 170ish stock would show similar gains, maybe even pushing it up to around 220FPS. But short barrelled units can be finicky and the law of diminishing returns applies.
Not much more that can be done given the nature of the gears and their doubtful longevity under hard loads. Next job is to bore out the outer barrel for fitment of an 11mm adjustable hop up, but a very simple mod and no rush for that.
But… 200FPS? Happy with that. 
Apologies for fhe length of this post, but the devil’s always in the details. Hope all this is of some help to anyone looking to get a little more out of their ZY UZI. Great little units.
2 Likes
Fantastic results…!!
I knew you’d like working on it…and saved Rok some legwork…!!
Well done…!!
Excellent work mate and a very comprehensive well written guide 
My old “trick” for those types of springs to gain slightly more pressure at full extension was to give them a gentle stretch to around 15-20mm of the original length before refitting.
Not ideal, but works surprisingly well when there were no other options available. 
Would you be able to upgrade that motor, get a bit more torque out of it, but as you pointed out that bevel-not-bevel gear is definitely the weakest link.
Wonder if those old BF gears for the Uzi/mp7 would work.
Oh yeah, you can get high torque, brushless, all sorts of upgrade 370 motors. The benefit of which is the grunt to pull a bigger spring.
But…
In my experience they aren’t worth the bother… you don’t notice much improvement… and you’re bang on when you say the gearing probably wouldn’t take it anyway.
Awesome write up and investigation work mate. LOVE IT!
And really glad to see it came up to a decent fps.
I had feared it would be loaded with proprietary parts limiting the possibilities and this is good confirmation of that.
Shorten inner barrel, spacer the spring, clean and grease. About all that would be worth doing to it by the looks of that crown gear too.
I am surprised to see only three gears, though it might have been four like the LDT MP7, but I guess it is what fits and works in the space provided by the receiver so cant complain really.
Again, awesome work and review. Thank you @Friendly_Fire
Doing the gel gods work once again.
Well, Beemer’s was getting 170FPS stock, the one on X-Force’s review was similar. Mine was only doing about 140FPS… maybe it was a Friday blaster.
But maybe if you’re starting from that higher FPS of 170, possibly just shortening the barrel might be all that’s needed to get it up around 200… and no need to split the gearbox.
Then again, add a spring space and it might get up in the 220 range.
Hopefully other members will do their own choice of mods and come up with an even better result. But I’m happy.
2 Likes
Makes 230 fps, out of the m92 a pretty good achievement…
Mind you, it has super solid metal gears…
Still…small barrel and volume…
Good result for an EBB pistol.
1 Like
Withe the Uzi…could you shorten the barrel, from the other end, and keep the hop up.?
Or just be done with it, and install a after,market one…?
I get 210 out of my MP9, similar size gearbox.
But the design of that one allows for a really short barrel, so better VE. I know when I was modding that thing I trialled longer inners and the chrono readings went backwards.
That short barrel in your M92 would be part of the reason it’s doing so well.
1 Like
If I got my hands on one it wouldn’t be difficult to model up one of those to be printed.
That barrel does look like it’s been machined down, like from 9.5 to 8.5 outer, not dissimilar to some GBB pistol barrels.
1 Like
It’s turned down at the hop up end to give a 10mm OD with the rubber sleeve on. Easy to replicate with a bit of lathe work and a file.
I still reckon an adjustable slim hop up will be a better option.
2 Likes
Quick update…
Just found out the inner barrel can be shortened at the t piece end. The collar is removable after all.
Understand though that popping off the collar and shortening the IB at the t piece means filing a flat on one side of it to allow for a detent strip in the collar, there to revent rotation and keep the hop up aligned.
The receiver also needs modification if you shorten this way. The factory diameter of the barrel hole at the t piece is 9.0mm, it will need to be opened up to 9.5mm to allow for the lack of machined groove or the shell halves won’t close up properly.
The posts above have been ammended to reflect this.
Still think it’s easier to shorten at the business end.