CYMA Complete Metal Gearbox for MP5 Series Airsoft AEG

"Got this guy to replace the gearbox in an 11 year old tokyo marui mp5 R.A.S. The sector gear stripped five teeth one day in the middle of an intense firefight, so I was a little bummed and I came on to Evike to get a replacement gear for it. I found no shortage of parts, but the more I looked at that old gearbox, the more I realized it was just worn away - I could've bought the new gear for sixteen bucks and have it fixed and maybe have something else go in a few weeks, or I could just save myself the headache of breaking down that mp5 (seriously, it's time consuming to open all those mp5 clones up, there's no way around it) and start from the ground up with a brand new pre-assembled gearbox (also cheaper here than anywhere else that I found, AND you know you can trust evike.)

So far it's working wonderfully and I have zero complaints. The wires that run to the motor are a little stiff is all and can be tricky to hook up to the connection terminals, but it's an easy fix - just limber em up a bit, almost like stretching a muscle - don't go too far, but loosen em up a bit. I would open it up a bit when you get it just to make sure that it's properly shimmed and greased (IF you know what you're doing, if you've never fiddled with a box before, just do your research first!). Mine was perfect, but lemons are bound to happen at least once or twice - particularly with gearboxes, only because they can require tons of finesse at times.

Anyway, highly recommended for someone looking for a standard plug and play box that's affordable and dishes out a pretty capable performance.

"I was not expecting much when I made this purchase. This gearbox is a replacement for my current mp5 that had serious trigger issues. The quality of the shell is standard pot metal so I would not recommend any high strength spring. I am comfortably using a m90 spring and it seem to be holding up. I discarded the original spring. After cleaning up the gears off and having a good shim job , it performed really well. Cylinder and cylinder head does not provide good air seal. The piston is pretty decent for what it is. For 40 bucks you cannot get the quality you are looking for. You get what you paid for. With a little know how, you can make this work . The gearbox is very smooth after tweaking it to my desire. I also installed a nano gate mosfet so i can use an 11.1v lipo. I would not recommend dropping this straight into your gun if you want performance. I believe the gearbox will still perform just fine if you didn't do any work to it but it would not be very satisfying especially for experienced airsoft players.

"Bought this while keeping the other review of how the gearbox casing is made of cheap pot metal. Which it was. I popped it into my mp5 lower and as it cycled its first shot. The top of the gearbox split in half. For the most part it makes for good gearbox parts. But the casing is just trash.

"The top portion of the gearbox snapped, everything else works but the shell is VERY low quality pot metal. Don't waste your money.

"gearbox came broken so i just took out the needed gears and replaced the old ones. I shouldn't have to do that.

"Horrible gear box. Put it in the gun to test then took it out to shim the gearbox and do a few other upgrades and the gearbox case halves were so badly cracked that the gearbox came apart (like exploded on the table) after removing the screws in front of the cracks. I knew it was a cheap replacement when I got it but didn't think it would be quite that bad.

"I am not a fan of leaving any negativity because evike is the best company for airsoft and have helped me many times with issues. Save the $39, just buy gears, shims and whatever other internals you need for your build.
The bushings are steel which I was surprised, but the play in all 3 of them shows how bad the shim job was. The bushings also moved which means they were not attached to the gearbox shell , which I found when I opened up the gearbox. I am surprised since CYMA is a quality brand.
Some of the internals seem fine. Here's the bad. The piston is not great but it has 1 steel tooth. The piston head is very loose, and the worst part is there is no air seal at all. I tried using teflon tape (dont ever use this) just to see if I could have a temporary air seal. Nope, didn't work. I cleaned everything since the inside of the gearbox was drowning in grease.
The good. Flexible tappet plate, steel gears, decent cylinder, nice ball bearing guide rod. that's it
DO NOT BUY this gearbox. The shell is terrible pot metal and will absolutely crack even if you radius the cylinder walls

"Very, VERY bad quality. Got two of these, both shells broke on the top area. Just used the gears and other parts inside to fix up other gearboxes. I do not recommend this at all.