"After 6 years of owning my trusty G&P, non-QC gearbox work gets old very fast - so I wanted an upgrade the shell. And this gearbox is a decent fit.
But if you consider using it on its own, you might as well replace a few parts - the gearbox has zero compression:
- Plastic nozzle. No o-rings; wobbles loosely on the head.
- Piston head or o-ring. Not sure if factory lube is old or just plain wrong but o-ring had shrunk and wonâ€™t seal.
- Trigger contacts. Made of shiny metal other than copper. Those have proclivity to oxidize in use.
- Trigger. Made of baked alloy. Not a deal breaker but feels cheap.
"$48 for a gearbox full of parts isn't a bad deal. This is a good option to update an older AEG gearbox to QCS and bearings at the same time (for example, I was converting a CA M15A4). I took notes while disassembling it for incorporation into my build.
-QCS system seems solid.
-Front shoulders of the cylinder windows are radiused (rear ones aren't, but that's not as important).
-Various internals you don't want to use for your build will be "good enough" emergency replacement parts.
-NO USELESS REAR REINFORCEMENT, so you can actually use Siegetek gears without grinding out loads of material first.
-Shimming is OK, not great.
-Bearings don't sit 100% flush to the gearbox shell, same as 99% of other airsoft gearbox shells. No worse than VFC's, G&P's, G&G's etc. that I've worked on. You could probably either polish down the surfaces of the bearings or use a mill to drive the pockets down slightly further to get them completely flush if it's necessary for your application.
-Practically no lubrication (at least you don't have to clean out an ocean of bad lube, I guess).
-Type 0 cylinder.
-Air nozzle does not have a shoulder like normal V2 air nozzles. This means you might have more blow-by in the hop-up unit. Not critical for CQB builds. It also does not have an internal O-ring, which compromises air seal.
-The spring seems to be an M100-M110. Couldn't chrono it because the piston O-ring seal was so bad. Gears are generic ACM-quality 18:1 gears with no branding.
-Piston head sucks, completely compromises air seal in the cylinder. Replacing the O-ring did not improve air seal (no air was leaking at the cylinder head).
-Full-steel tooth rack on the piston, including pickup tooth (this is bad for most gears, and I'd rather blow a piston than a gearset).
The gearbox is okay. It's about on par with any other ACM gearbox, while not costing anymore. Good for parts salvage, but I wouldn't use this as-is in my guns.
How I'm using this:
I am replacing everything inside of the gearbox shell with SHS/ZCI parts and a Gate Aster V2 from the host gearbox. I am keeping the cylinder head, cylinder, gears, tappet plate, trigger, trigger contacts, and wiring for the field repair kit. I am disposing of the piston and piston head.
How to make this work completely great for an all-around build:
Re-shim the gears from scratch. Lubricate the gearbox properly (white lithium for gears, bearings, and piston track, silicon for cylinder and piston head). Replace the piston with one that has half metal teeth or only one metal tooth. Replace the piston head with a higher-quality polymer piston head. Replace the air nozzle with a shouldered type that has an internal O-ring. These parts will improve reliability, fix the air leak problems, and vastly improve FPS consistency. The gearbox could then probably take up to an M150 spring without concerns. I wouldn't personally go above an M130 until I'd replaced the gears for a higher quality set, but ACM gears have gotten better the past few years, so upgrading them may not be necessary.