I'm tired of working on KWA guns that are broken. They're a pain in the ass, and frankly, they're expensive to maintain compared to almost every other gun on the market because you're stuck buying KWA parts.
Here is a list, partially compiled by me, and mostly from other techs I know, about some of the bad things about KWA products.
18gauge wire which is too small for the amperage even a mediocre AEG will draw
Gearbox Painted inside and out (leads to paint chips inside the gearbox)
Spring guide tabs break frequently
9mm bearings (frequently reported to fail)
Trigger trolley stop (too thick; blocks use of some gear sets)
Trigger contact/trolley failure due to load (didn't bother using a mosfet, dispite their "lipo ready" claim)
Electrical (selector plate) safety which can short/corrode
Trigger axle to trolley height off spec (replacement trigger units won't work)
Cylinder head retention nubs over-sized, wont fit non-kwa (ie: standard TM-spec)
Gearbox "reinforcement" material over allowable width
Flexing upper/tab failure/piston forward requirement to open
Full floating barrel (both ends) reduces accuracy/not GB justified
2GX bucking
Hop chamber off spec (other bucking incompatible)
Aluminum flat faced piston head
Insufficient cylinder head buffer (read:broken gearbox shell)
AOE adjustment absent
Unported piston head (all sorts of problems can occur ... ultimately it makes the piston,gears,and motor work harder)
plastic hop unit (two piece proprietary)
Tamaya connectors (multiple in some models) (high electrical resistance, which gets worse as they heat up from full-auto use)
Un-vented grip on many models
ferrous motor (low torque)
Grip connects to gearbox with only two screws
Self tapping screws (don't hold torque very well, easily strip, when they strip they are different than every other gearbox on the markets thread pitch and design)
No bearings on spring guide and piston head (washers adding mass to the piston assembly)
Springs not ground flat
Lack of piston tooth reinforcement (strips pistons)
Gear axle center distances off-spec (there is a difference between "kinda fits" and on-spec.. which can lead to catastrophic failures down the road even if it "works" right now)
unshimmed from factory (new "self shimming" features) ... which WILL eat itself alive over time, whether with using high amperage lipos or not.
The precision needed for unshimmed gears was never seen in a KWA gun. They took short cuts instead, to keep everything running well. Their bearings are a good example. One issue they have is that the gears are not made to proper spec, so the gears will actually get stuck in the bearing posts, meaning they are impossible to shim. However, because they are in bearings, they still spin. Even when the parts are well made enough for the gears to properly sit in the bearings, they are not shimmed, the gears are loose and wobble in the gearbox. This magnifies the issues of a painted gearbox and weak bearings, as this can increase the likelihood of the bearings failing and increase the wear on the inside of the gearbox, increasing the paint chips..
Not to mention, there is no mosfet... which again, means it is not lipo ready.
TL;DR: There are a lot of proprietary parts in KWA aegs, and while they might shoot "fine" stock, for a while, as soon as you want more from it, it will require almost full gearbox and internal parts replacement in order to be truly reliable.
Granted, many of the problems listed here are present in other companies as well, but none of them collectively have this many issues, or at least none of the mainstream reputable companies do.
Many of the issues are intentionally done by KWA to ensure that people HAVE to buy KWA replacement parts, which they seem to design with engineered obsolescence in mind. Intentionally making weak, proprietary parts which will fail, and forces you into a market they alone control.
Credit to HS5, and star_folder from airsoft society and mechanics for their helping to compile this list and some of this info.
