Classic Army Ump Gearbox Rebuild

[THE FNG]

Hi all,

Looking for some advice with fixing my classic army ump. I need some help with picking the right parts to swap out.

Firstly the piston stripped so I need a new piston. I will also need a new piston head and o ring as the stock one got damaged and are no longer useable.

The gears, AR latch and motor are ok. I think the tappet plate and cylinder are in order too.

My question is, what do I need for a stock/normal-ish build? I'm not seeking to turn it into some 900000 rps monster; just something with a respectable trigger response which it wasnt far off when fully stock and working.

At the moment, all parts are stock.

I was hoping to use parts available at ak2m4 if possible as I will be putting an order in soon for some other bits for another project.

Edit: whilst I'm browsing ak2m4, can anyone point me in the right direction for some trigger contacts for a g&p sr15?

 

[Adolf Hamster]

https://www.ak2m4.co.uk/internal-parts/pistons/cyma-15-tooth-reinforced-piston

https://www.ak2m4.co.uk/internal-parts/pistons-heads/gearparts-pom-piston-head

would be a pretty basic (but not bad either) replacement.

if you wanna be fancy you could grab some of the aoe spacers, but for a low stress build probably ain't gonna matter too much.

potentially if the nozzle doesn't have a sealing o-ring then might be worth looking into getting one (just be sure to measure the length proper), will help air seal (and by extension accuracy)

if you're happy with the speed as-is no point changing gears/motor etc.

apart from that it's all in the assembly, shimming, air seal checks etc.