Today we took down the Unicorn to downgrade it for indoor play. Even with the hop on I couldn't get it to shoot below 350 on its own so a new spring needed to be installed. We chose a stock TM spring that had previously chronoed at 285 fps.
Unfortunately I didn't think to take pics along the way so try to imagine this as I go along. The hop unit is screwed down into two steel rails that appear to be a part of the trunnion, which is riveted to the receiver. Near as I can tell there is NO taking down of the trunnion. I don't really mind because I like the cleaner, authentic look it gives versus the multiple screws on the CYMA. Disassembly is a matter of unscrewing the Allen screws and pushing the hop forward towards the trunnion, then pivoting the gearbox out. The hinged top cover is also permanently fixed in place so you have to rock the box out.
The gearbox appears to be a CYMA unit, marked CM.02. Nothing too remarkable about it. The nozzle is clear as is the spring guide, and aren't too confidence-inspiring. They were replaced with a Deep Fire M4 nozzle and a CA V3 bearing spring guide.
Due to the steel receiver being thinner there is much more room around the sides of the gearbox in certain spots. Other supporting areas have been shimmed with steel plates inside the receiver. Notably, on the left side of the receiver towards the back, there is a nice channel for which to run wires down to the motor. A silicone-sheathed 14 gauge wire was selected to replace the stock wiring. In our experience most AKs cannot even take 18 gauge silicone wire as it's just too tight in the pistol grip but the Unicorn is different. We decided to stick with the stock wire leading from the motor to the selector plate and replace the rest, which fit perfectly. A Deans connector replaced the Tamiya.
Pictures of the final result were taken but I don't have them yet. The difference was a marked increase in rate of fire and trigger response time, partly due to the increased conductivity of the Deans connector and wiring, and lighter spring. I expect it to chrono around the 300 mark which should be just right for XT games. Rate of fire is perfect for this gun which typically achieves a slightly higher ROF than a full size AK due to the shorter barrel system. I am extremely pleased with the results of this simple mod!