So begins the slew of overhauls to come for my newest toy, a Tokyo Marui HK416 “DEVGRU Custom” Next Gen AEG.
I started with a complete Army Force (AF) gearbox assembly… bought for gearbox shell bushing size & spare parts (and because I was honestly a little afraid to open up a like-new Marui Next Gen AEG for the first time without really knowing what I’m doing yet).
I began this process by lightened up the trigger spring – personal preference when it comes to AEG’s. It didn’t help that the trigger return spring was annoying strong when trying to keep the gearbox all in one piece when I popped the shell open. I did not modify the AF switch as it appears as if it would complete the circuit fairly early in the trigger stroke.
AF mechbox is 8mm – whole reason why I wanted it in the first place is for metal bushings that are of a more standard AEG size than TM’s 5.9mm. That being said, I have read that one could open up the bushing holes in a Marui shell, but I’d rather take the lazier route. We’ll see if this pans out for me or not, as the two halves of the gearbox shell don’t fit as precisely together as I would have hoped for (not as good as Marui original parts) – it can be lined up fairly easily though, and I wouldn’t call the fit sloppy after all.
The next few photos are ones I took for reference. I do this nowadays when I disassemble & reassemble a new toy for the first time – especially if it is something that is not well documented.
Gearbox required some polishing inside – a few bits of some sharp casting was rubbing on my gear set during the shimming process. Fast and easy fix with a Dremel. To be honest, I’m surprised that I didn’t find anything unexpected or much worse than this inside.
8mm bearings (probably G&P?) were installed for bevel gear while everything was apart. While I’m not convinced that the Next Generation AEGs even need this, smoother is better, provided I don’t take a reliability hit with my spring in mind. It turned out that dropping in bearings for sector & spur gears got in the way of the selector plate’s travel – perfect, as I found that high speed gears/torque motor gearbox builds on M120 and 11.1V can shred up to a 8mm bearing real fast (and this one will be much less crazy).
I will need to figure out a way to route the wiring in this gearbox out to the rear for my HK416… but that will come later when I pull out the original Marui box for preservation of the OEM parts. May as well upgrade to silver cord at that time too (though I’ve read that the current rear-wired battery set up as is from TM is fairly inefficient already).
Ported piston head & piston body look good enough – disconnected the main spring and chopped off the coil that retains it to the piston head. Out of box air seal is a joke in this gearbox. No wonder why the Army Next Gen clones have such inconsistent FPS from gun to gun. Swapped new piston head O-ring but with no major improvement. Needs something more…
New cylinder head O-ring and still loss of compression out the front with the AF cylinder head – plumber’s (teflon) tape for quick gap filler will do the trick for now. Cylinder (3/4 port) is practically the same diameter as standard AEG, and I will be doing more research into balancing cylinder ratio with future wide bore Orga barrel (why buy the Orga kit if I can find an appropriate [un]ported cylinder that fits?). Surprisingly, the stock AF air nozzle makes a fairly decent air seal with cylinder head – while not perfect, I find it passable for the time being.
Left to right: Lonex, SHS, AF. Note, all are same ratio gear sets (6 turns of bevel gear for 1 turn of sector gear – not sure what that translates to). Lonex looks to be of highest quality at first glance & features a longer tappet plate delay, while SHS and AF initially appear to be almost identical. The AF complete gearbox gear set was not shimmed correctly out of the factory (super loose, 0.3mm shims only) and the spur gear is most likely warped on its axis. I replaced it with the SHS set as I intend to use the nicer Lonex set in my TM Recoil Shock SCAR-H (with a higher FPS goal in mind).