Gearbox work leaves gun inoperable

[Mister Cak]

Hey guys,

So let me set the scene for you first:

"Been doing organized airsoft for awhile, and decided the next gun I was going to buy would have to be easy to work on so I could learn to do all the technical stuff."


So I open up my P90, first time I ever opened up a gun, my goal was to change the spring. I follow an Echo 1 video on youtube, he says its ok when you open up the gearbox and everything falls out. Except now I have no idea where everything goes. I followed another video on trying to put it back together, Since everything fell out I had to reshim the gears, and then complete the upgrade I set out to do in the first place...


The first time I did it, put it all together I couldnt get the GB case to close: http://www.youtube.com/watch?v=_5-2KJnu ... QR1v3-n45B


So I go back in, move things around, and finally get it closed. I attempt to shoot the gun with 4 different batteries and find no response. So I take out the GB again, and I pull back the part the trigger pulls back, and I get a loud click, just once.

I finished opening up the gearbox, and my ARL always seemed to put my last gear off balance and I have no idea why, the other issue I had is when I installed and even previous with the default spring, the piston ALWAYS bends in a way like it wants to jump out.

So my completely noob opinion is that either the gears are getting stuck, or possibly there is something stopping the piston from being pulled back...Here are some videos of when I just took it apart again:

Exactly how it was when opened this morning:
http://www.youtube.com/watch?v=k7PwRUDn ... -dGQat4cUc

After taking things apart:
http://www.youtube.com/watch?v=2rIsGFFV ... QNpPr7rnvK

If there is anything I can get a picture of, or make a tape for, or explain better please let me know. Again I am completely new at this so I just tried to provide as much info as possible. I have literally been working on this for about 12 hours over two days, which is just pathetic I know.

Thanks for your time and help everyone,
Mister Cak

[Hotspur93]

Its alright I had that same reaction when I opened up my first GB. Anyway, when you put it back together to test fire, it did nothing even with all your batteries? I know this is stupid but first check to see that your batteries are charged also did you check the angle of engagement? Meaning was the sector gear lined up with the piston when you put everything back together? I know that one attempt I had at putting my GB back together the sector gear got stuck on the piston because I hadn't lined it up correctly.

[Mister Cak]

It may be AOE as my piston seems to be arching. This happens with both my downgrade spring and the guns default spring, they are nearly the same size.

http://www.youtube.com/watch?v=mFxYZWaQYp0

[Star_folder]

Your AoE isn't causing your piston to arch, it's the main spring inside of the piston that's pushing everything up. You're pretty lucky that everything is staying in place as well as it is. Usually the spring guide and/or cylinder assembly will pop out without the upper gearbox shell holding it down.

You are going to have to keep that pushed down when you put the upper shell back onto the gun. Something else that that spring is doing is pushing your cylinder head, causing it to be slightly misaligned. My suggestion is to make sure the upper gearbox shell is meshing properly with the cylinder head, then slowly close it in an arching pattern, pushing and moving everything in a way to make it fit into it's holes.

You should encounter the spring guide first, use a screw driver to push it in a little so that it fits into the upper gearbox shell. Then use a very small screw driver, or something strong with a point, to move the gears around until they fit into their respective holes.

As for the gearbox clicking, I'm 90% sure it's got to do with your shimming.

When you shim a gun, you need to test it with the gearbox closed. Remove all the extra stuff, and just have the gears, bushings, and shims in the box, and put a few screws in around the gears. You should be able to flick the gears with your finger and have them spin a few times. If that's not the case, then it's shimmed much too tightly and you'll need to move stuff around.

[Mister Cak]

I have been trying my best to do my research on shimming, ive read a few guides, and watched videos. The main issue with the thread here on the forum, the video shows the gears already shimmed. So my confusion comes from this...

The gun came with two shims per gear, from what I understand you add more or less to shim it? I think I have to be mistaken as it was operable with the same shims by default. I know I confused myself but I am not sure where.



The latch outside of the gearbox is stopping the gears from moving when I test to see if they are spinning or not, but when I hold it up, the gears move freely. So my question is what is that latch and why is it stopping the gears from moving?

Here is what I was talking about: http://www.youtube.com/watch?v=qYK8xEdp4ps

[Star_folder]

That is your cut off lever, the main reason why semi auto works. You should remove it when shimming a gun so that it doesn't slow down the gears like that.

Also, you need to test the shimming with the gearbox closed.

Do you have the exact same shims on each gear as it came with stock? I think you are going the wrong way with this, or, rather, you have the wrong idea. It's not about numbers or measurements. You have to look, and see the gears to shim the as they should be shimmed. ... I'll make a guide later this week as I've got a gun that needs to be shimmed, that should give you a good idea of how to properly shim a gearbox.

Here's that thread I told you I'd make.