MP5K-PDW mechbox/trigger problem

[Xular]

I was fidling with my MP5 last night and i noticed something weird. I was dry-firing (with no battery) and seems like there was a small problem with the trigger action

when in full auto, i just pull the trigger and le trigger goes back smoothly. but when im in single shot, there is something restricting the movement sligthly, as if there was some sore of clicking at mid-travel. nothing hard, but still enough to find it disturbing

also, the single shot is very hard to find with the selector switch.

now this is a first for me, ive decided to open up the mechbox. nothing looks damaged, every think looks in place acording to diagrams found on web.

anybody can help?

also, what kind of grease/lubricant should go in there? im sure every body has there own preference... and since the mechbox is openned, maybe should be going for upgrades... not really looking for more FPS, looking in reliability as a first. wich company makes the best internals?

thanks

[Maverick0]

I've got a PDW as well and I find it's not difficult to find the semi setting, it's just that it seems to have an extra click before it gets into safe.

I have some problems with Semi auto as well, but I'm told that's pretty common. The gun will jam sometimes in semi auto, but a switch over to full fixes the jam.

As for upgrades, I went for the reliability route as well. First things I changed were bushings, spring guide, piston and piston head. I have a some sort of polycarb piston, a systema silent head and a systema spring guide.

I eventually changed out the gears and the spring and put in an anti reversal latch and finally a tight bore. It doesn't shoot particularly hard, but it gets great range and good ROF. Hasn't let me down in a year and a half. No repairs so far

[Disco_Dante]

I have the same problem with semi auto where it jams, but a switch to full fixes it. Does anyone know what causes that, and how to fix it?

[ShelledPants]

Ok. I'm terrible with proper names, but this is my theory on this as I have experienced it with my own MP5K.

In single fire, when you pull the trigger, the electrical circut is bridged and spins the motor. This in turn rotates your gears. As your final drive gear engages your piston and spins, it moves a latch which prevents the gun from firing in full auto. Releasing the trigger resets the latch and allows you to fire again, with the next pull of the trigger.

The problem occurs when your motor spins too fast and the piston is engaged twice in a single trigger pull, but not all the way, meaning your piston is half cocked. "Well I should be able to pull the trigger and just finish the cycle!", nope, the latch is in an awkward position and will not reset.

The solution is to switch to full auto, which allows the switch to be bypassed and odds are when you finish pulling the trigger, the piston's cycle will not be in a position to catch the latch, and you can now fire in semi auto again.

I would like someone to confirm with me, that this is the likely issue, and if they want, to paraphrase my post with the appropriate names. I'm at work and can't be bothered to go look up all of the terms for gearbox internals. xD Sorry. I hope it was all legible.

PS. The catch is located on the left side of the gearbox, just above the trigger group, I doubt it is the latch which is causing the problem, as it's more likely your motor spinning too fast for your gun, maybe a MOSFET with active breaking is a better solution then slowing your RoF.

EDIT: Note that I only began experiencing the problem after installing a 9.6v battery in my PDW. Did you do the same?

[Jimski]

I have the exact same problem with mine

[Invasian]

ditto

[Schwag]

I have the same problm with my echo1 pdw

Is anyone having this problem with marui/ca or just clones?

I think shelled pants may be right. I have also found that the trigger return spring was too strong (snapped eventually) and that may have had something to do with it as it hasn't clicked or stuck since the spring broke(haven't replaced it yet)

[ShelledPants]

Originally Posted by Schwag

I have the same problm with my echo1 pdw

Is anyone having this problem with marui/ca or just clones?

I think shelled pants may be right. I have also found that the trigger return spring was too strong (snapped eventually) and that may have had something to do with it as it hasn't clicked or stuck since the spring broke(haven't replaced it yet)

Pfft. Just super glue the spring...

I find I exacerbate the problem when double tapping rapidly. On TM's (MP5A2) all that happens is you half cock the second shot, but on my ECHO1 (MP5K), it tends to cause the clicky-no-worky as described above.

EDIT: I realise there is a difference in mechbox, (v2 and v3) of the Mp5A2 and MP5K. I was just making an example.

[Disco_Dante]

My mp5k is a TM, and i have that problem.

[CDN_Stalker]

Last weekend I found that a teammate's TM MP5K had a sticky contact between the trigger and the little pivoting linkage that pushes the trigger contact bar forward. After a lot of filing and screwing around, I found the part that was causing the problem to be the top of the trigger where the linkage meshes with it. Shitty description.

The black peice and the grey metallic peice the trigger pushes forward. Top of black piece that sits in and pivots in the linkage. I used my Dremel and ground down the top of the black piece. Wasn't sticky any more, my problem solved.

[p.phresh]

apparently there is a fix for the jammed/semi-auto problem you are all experiencing

There's a part called a sector gear chip. It goes on the sector gear facilitating a delayed tappet plate action.

dunno how well it works.