Retro Arms aluminium CNC gearbox ver.3

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The examination and comparison of the CNC gearboxes continuous. This time we have ver.3 gearboxes made by Retro Arms and X High-tech/Combat Gear.

1. Retro Arms ver.3 QSC gearbox with spring guide and screws.

From the technical point of view the ultimate difference between these two is in the process how they were made. The X High-tech gearbox is casted first and then milled (or if you prefer - polished with CNC). The one from Retro Arms is completely CNC machined out of the solid block of aluminium AW EN7075 T651. This difference can be easily noticed on parts like spring retaining pins, parts which hold the cylinder or selector plate spring guide.


2. Selector plate spring guide and tappet spring retaining pin of the X High-tech gearbox.


3. Selector plate spring guide and tappet spring retaining pin of the Retro Arms gearbox.

Retro Arms improved the 3rd version gearbox classic design by getting rid of the rudimental upper tension strap. Its upper part tightened by 2 screws instead.


4. Upper screw slots of the Retro Arms gearbox.

5. Upper part of the Retro Arms ver.3 QSC gearbox with installed bearings.


6. Lower parts of the Retro Arms ver.3 QSC and X High-tech gearboxes.

For more precise and easy assembling there are small lugs and notches on the sides of the gearbox.


7. Lugs and notches of the Retro Arms gearbox.

The top of the X High-tech gearbox is held by the standard tension strap. The centering and locking of the gearbox sides during the assembly is assisted by the bulges and grooves made around 3 screw holes.

8. Grooves inside the X High-tech gearbox.

This particular gearbox was used in the MG36. As can be seen on the photos below there are quite many parts where the metal is severely worn out.


9. Worn out metal under the G36 safety mechanism.

Especially on the guides of the piston and tappet.


10. Tappet guides inside the X High-tech gearbox.

11. Tappet and piston guide rails inside the X High-tech gearbox.

The marks on the bearing slots mean that the bearing outer rings are rotating inside them.


12. Bearing slots of the X High-tech gearbox.

Compatibility
During this review Retro Arms gearbox was installed in the MG36 (based on Tokyo Marui G36C) and LCT AK-74. Few noticeable aspects were discovered.
There's a protrusion on the lower (left) side of the gearbox which obstructs the G36 tappet plate. This can be fixed by filing off the tappet plate where it interferes with the protrusion.


13. TM G36 selector plate on the Retro Arms ver.3 gearbox.

14. Protrusion on the lower side of the Retro Arms gearbox.

15. There's no such protrusion on the X High-tech gearbox.

The AK tappet plate moves without any problems. But the lower (left) selector sector gear is too thick for the gearbox hole. This happens quite often with gearboxes and selector gears from separate manufacturers. Then again it can be fixed easily with a simple filing.


16. Left selector sector gear of the АК fire selector mechanism on the Retro Arms gearbox.

Few cylinder heads were also tested for compatibility.
The Systema Energy cylinder head base was a bit too long. In this case it should be sawed at the front or its mounting holes widened out.


17. Systema Energy cylinder head.

The Lonex ver.3 head is not compatible with the gearbox because of its front projection. The Retro Arms gearbox has a groove in this part, but it's round-shaped while the Lonex head projection has straight lines and angles.


18. Lonex ver.3 cylinder head.

19. Front part of the Retro Arms ver.3 gearbox.

The Tokyo Marui stock head fits by size but might require some widening of the holes.
The Jing Gong head fits well.
The Retro Arms Universal cylinder head (for 2nd and 3rd gearbox versions) fits precisely.


20. Retro Arms Universal cylinder head.

Its design and rounded damper should allow the use of flat and silent (cone-type) piston heads. In this case it was used with the Systema Energy silent piston head, which immediately set the angle of engagement (AOE) close to perfect. Just bare in mind the 2nd piston tooth should be sawed off. And filing half of the 3rd one might also be a good idea.


21. Retro Arms Universal cylinder head and Systema Energy piston head.

There were no problems with the pistons themselves though. The Modify Quantum, SHS and Tokyo Marui/A&K/JG worked out flawlessly. Only the Azimuth might require some minor filing due to thicker slides.
The Retro Arms piston with full metal teeth is obviously well compatible with the gearbox and moves on the piston guiding rail without a flaw or some noticeable play.


22. Retro Arms piston.

It doesn't have a 2nd tooth and only a half of the 3rd one by design. This is vital for the systems with high rate of fire and for correctly setup AOE. Its metal teeth machined out of the 12050 steel.


23. Retro Arms piston.

The piston plastic body has a few cosmetic flaws, which I hope we wouldn't see in the next batches.


24. Retro Arms piston.

Other interesting and useful features of Retro Arms gearbox:

• Window for anti-reversal latch release
• Small grooves on the pins which securely hold the tappet and switch springs
• Precise slots for anti-reversal latch and trigger hold them firmly without a chance to jump out
• Rigid M3 Hex screws
• QSC metal spring guide with bearing

As for the price, the Retro Arms gearbox along with the 8mm bearing set costs $123.
You do the math: for the cost of the Chinese nominally machined gearbox you get improved, fully machined from scratch gearbox with the lifetime warranty from the actual manufacturer.


25. Retro Arms ver.3 QSC gearbox with full metal spring guide and screws.