Question about gears....

[buttonsHT]

So I purchased a used TM MP5 that wasn't working properly. I've never disassembled an AEG before and figured I'd give it a try on this one using an online guide. Things went well and I didn't lose any screws or springs. Now once the gearbox was open I found this....



This seems to be the only damaged part in the gun. Can anyone tell me what would cause this? Or anything I should look at for damage?

It's a stock MP5. Nothing special in it.

Thanks

PS. I did order some new gears from AirsoftStore so I'll have those next week to install and get it back together.

[ThunderCactus]

gun probably jammed at some point, maybe a BB got stuck in the barrel, sector gear picked up the piston before it was all the way forward, and the mechanical shock of the mechbox coming to a complete stop was taken out at it's weakest point. In this case, the teeth on the spur gear. Some gears are much weaker than others.

Inspect the piston for damage, otherwise pick all the teeth out of the box, install and shim the new gearset.

[buttonsHT]

Thanks for the tip.

I completely forgot about shimming (i read up on changing gears a million times last night) so I just messaged Stealth about grabbing some.