Úvod / Aktuality


01. 02. 2015


This is my first review in a series of reviews for RetroArms products. This review is about the RetroArms 8mm V2 gearbox shell. Further reviews will be about:



The goal of this review is detailed description and testing of compatibility of the RA gearbox shell with stock AEG parts and some aftermarket parts. This review is not about the strength of the gearbox shell nor the making process. For this information please visit:



For more pictures,please go to:




RETROARMS 8mm CNC gearbox shell


What do you get?


The gearbox shell comes in a black cardboard box with a big RETROARMS logo, no other text on the box. Inside you will find the shell in protective foam. You will receive the shell and a set of screw for the shell. Notice the 2 smallest screws. These are for the cut-off lever and the trigger switch.
http://i57.tinypic.com/11tvc6x.jpg - http://i60.tinypic.com/o6zfo4.jpg


First impression


First thing you will notice is that the shell is very light! Second- it is shiny! If you try to split the halves in two, you will notice it is a bit tricky. Even without screw at all, the gearbox halfs stay connected. Impressive! The gearbox shell is perfectly machined.






Informations provided by the manufacturer
„We developed our new gearboxes from Dural EN AW 7075. It is made from a single piece of aluminium on CNC...
Gearboxes are not casting as "Asian" brands! Gearboxes have long been tested on M160 spring without any signs of wear and tear.
So, it has completely different behaviour and it is almost indestructible. We guarantee compatibility with nearly all known brands of weapons. “


More info: http://www.retroarms.info/gearboxes/


To mention is the radiusing of the front part of the gearbox shell. You can choose between the 7,8 and 9mm version. It is up to you.


Compatibility of the RA 8mm V2 CNC gearbox shell with stock AEG parts and aftermarket parts.


Before i start with each gearbox component, it is important to say, that the RA gearbox shell fits into all M16/M4 metal bodys, that are made for TM type gearboxes. I have tested it for fitting in my CA A1 metal receivers. This CA receiver is tighter made, however the RA gearbox fits inside without any issue. The holes for receiver pins align perfectly. The RA gearbox shell fits even easier into the JG metal receivers, due they are a bit larger in the inside. The pistol grip fits nicely- no mods needed.
The manufacturer garanties compatibility with most other brands, however it is worth to give it a test.






I have tested a few different cylinders for fitting. All stock (barss) cylinders fit without any issue, the same with some aftermarket cylinders. Be aware, due the large number of different brands that appeared on the market in the last few years, it can be that some wont fit. It was not possible for me to test every brand. I do have testet stock cylinders from- JG, CA, Cyma, KA etc. Only the JG cylinder ( the one from the full metal M4 series with MOSFET) does not fit so good. It seems to be a bit larger in outside diameter, all others fit without any issue.


Cylinder head


So far i could figure out, all cylinder heads fit- stock and aftermarket. If any wont fit, it can be modded to fit. Most of the time are the holes on the cylinder head that need to be enlarged. Other than that, i'm sure there will be no other issues.




Tappet plate


All tappet plates fit nicely. However, you will need to pay attention when closing the gearbox. Make sure the tappet plate is in the correct position so the gearbox shell can be closed. Just doble check it.
Nice detail on the shell is the spring post. It has a grove, so the spring stays perfectly centered and can not slip off.




I have testet a few (TM, JG, CA, KA etc.) and the SHS piston. All except the red JG piston fit perfectly. It seems that the red JG piston has bigger rails, so it can not move freely back and forth. I this, by trimming the piston rails, even this piston would work.


Spring guide


All V2 type spring guides fit the RA gearbox shell.


Bushings and bearings


This shell i'm reviewing is a made to accept the 8mm bushings/gearings. The openings for the bushings/bearings are perfectly centered and allow a perfect shim-job. Even thicker bushings fit perfectly and don't make any issue for the shim-job.




Because of the perfectly positioned bushing/bearings, the gears match eachother perfectly, same for the spur-gear and piston teeth. If you do a perfect shim-job, the gears don't stop spinning! I have testet most stock gear sets and all of them fit perfectly. Only issue is with some gear sets that have thicker gear axle/shaft, it does not fit for some bushings/bearings. The SHS 16:1 gear set fits perfectly!




Anti-reversal latch


The base for the ARL spring is correctly positioned. The base for the ARL shaft is the right height, to the ARL engages the bevel- gear correctly. The hole of the ARL base is on the left/lower gb half is correct size, but bigger than the hole on the right/upper gearbox half. You must try your ARL for fitting. I have noticed that some ARL's have the upper parts of the shaft larger than the lower, so it might not fit into the hole. If this happens, just widen the hole. Out of 10 ARL's tested, only 1 has this issue.




Cut-off lever


All stock and some aftermarket ( Guarder) COL's fit perfectly. Only the SHS COL's have fitting issues. The hole is too small and has to be widened. One of the SHS COL's had even differently shaped arm, so it would not engage the trigger switch trolley correctly.
RA COL fits perfectly!
At the beginning i have mentioned the 2 small screw that come with the gearbox. One fo them is for the COL. However, you have to flatten the had of this screw so the head does not engage the sector gear.


Trigger switch


It appears that the stop-shaft for the trigger trolley is about 1mm machined to the right. It seems that way, because non of the tested trigger switch housings fitted without the same modification. One little corner of the trigger switch housing engages the shaft and prevents the housing to fit. Just trim off this part and it will fit perfectly. 5 sec. mod. Also, some trigger switch housing hae on the bottom parts,in the right upper corner a small piece of plastic sticking out. You have to trim it for the housing to fit perfectly. Other than that, trigger switches fit correctly.
The second small screw form the set you get with the gearbox is for the trigger switch housing and it fits without any mods.






The M4 trigger fits perfectly and does NOT fall out. It stays in place. Also it engages the trigger switch trolley perfectly!




Trigger safty bar


The trigger safety bar with all its parts fits perfectly into the RA gearbox shell. There is nothing more to add about this.


Selector plate


The selector plates fit without any mods. You have to keep in mind, to choose the correct selector plate. It depends of what size bushings/bearings go into the shell. The SP slides over 2 bushings/bearings, so the SP has a channel at its underside. For example- a SP that was on a 7mm gearbox shell will not fit the RA 8mm V2 gearbox shell. You'll need to buy a SP for 8mm shells. I had one SP for 8mm shells and it fit perfectly.






There is plenty of room for wiring. Interesting is that the manufacturer, made the lower part of the gerbox shell (where the motor head goes thru) deeper, so thicker wires can fit better and don't get ripped by the motor head. Very nice touch!




The RetroArmy 8mm CNC gearbox shell i very well made. As the manufacturer guaranties, almost all other brand parts fit correctly. Any incomatibility of any part can be solved with minor mods. Only thing to keep in minde is that the shell is CNC machinded and that the edges are sharp, so not to cut the isolation of your wires. I totaly recomend buying this gearbox shell!
I will be completing the gearbox shell and reviewing the process. Stay tuned!


Rating: 10/10


Greeting from Croatia, Osijek!


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