Gearbox wont cycle

[Smith5]

I opened up my first gearbox this week, but I'm having some issues getting it back together properly. It is a V2 gearbox from a Galaxy MP5PDW. The gun worked perfectly before I took it apart (except for the horribly broken body, making it useless as an AEG, hence why I'm now using it to learn about mechboxs!) Nothing inside the box is visually damaged, everything looks to be in order.

 

The first time I put it back together it would only fire full auto, even when the selector was set to semi. So, I took it apart and reassembled it but now it won't turn over. The motor is still fine and runs when not inserted into the gun. Any suggestions as to what could be wrong here?

 

Thankyou

[Jamanyar]

Can you post a few pics of the internals of your gearbox, just to see if all is put back correctly.

 

Any more info pls, as off the top of my head and without seeing what the problem is i could make a number of suggestions but that would involve writing a loooong post!!!

 

 

J.

[Smith5]

This is how it all looks as it sits on my table at the moment. In this arrangement it wouldn't cycle when it was in the gun. I haven't altered anything, just taken the half of the casing off to expose the insides. The bevel gear is back against the anti-reversal latch.

 

 

I guess it would also be worthwhile giving a bit more detail about when I did the first time I opened the box up. I removed the spring and cylinder assembly, the trigger and the gears. The shimming out of the box was atrocious, so I sorted this out and now it is much better. The gear will spin much more smoothly and freely now. I then put the whole lot back together and put it back in the gun. This is when I found it would only fire full auto, even if the selector is set to semi.

 

I took the gearbox apart again to check everything was back in and seated correctly, it all seemed to be. I put it all back together, again it cycled but in full auto only, then seized up. I opened it up for a third time to reset everything. This time when it was put back into the gun it would not cycle again. All I heard was the feint click of the motor trying to push against the gears, but not being able to turn. I checked the motor would run out of the gun, it does, so I assume it is not a problem with the electrics.

[Jamanyar]

Hey,

 

Are you sure the anti reversal latch is set in the correct direction?

 

First thing to check.

 

Then if that is ok. remove the cylinder, piston, spring (the while pneumatic set). Close the gearbox, you only have to use a few screws to make sure it is shut tight, then through the gap in where the cylinder was try to use your little finger to spin the gears. IThey should move freely in the correct direction (the sector gear should move counter clockwise) and lock in the reverse. I normally do this without the anti-revserssal latch to make sure the shimming job was done correctly, but in this case leave in to test if that is causing the gearbox to seize.

 

Hope that helps for now!

 

J.

[Smith5]

Right, I'm sure the anti-reversal latch is in correctly, pushing 'up' onto the gear, with the flat edge engaging firmly against the notches if I try to turn the gears in reverse, preventing their backwards rotation. The gears also turn nicely when it is just them in the box, with none of the other parts installed so I am happy with the shimming.

[Jocke]

Fist of all, gearbox in PDW and kurz is v3, not v2.

 

For the problem with semi, check if there is a little spring at the top of the selector plate, when you switch from FA to semi, this spring operates cut off lever inside the gearbox. If it's lost, gb won't shoot semi.

[Smith5]

The small spring you mention is still in place and the anti-reversal latch is returned to position when the selector plate is moved away from the full auto position. I have put the box back in the gun now, it is still not turning over.

[Jamanyar]

Are you sure the motor is wired correctly..

 

I've made this simple mistake many times, simply makes the motor turn the opposite direction hence it locking the bevel gear onto the anti reversal latch!

 

J.

[Smith5]

Right, may finally be making some progress. The motor is definitely wired in correctly. What I have just done is lowered the motor as far back out of the gearbox as is possible. I got a very pathetic whine out of it and the piston had been pulled back almost enough to complete a cycle, but now it has jammed up again. The battery is my best one and is fully charged, so Im sure there is sufficient juice for the motor to call upon.

 

Edit: VICTORY! It now all works perfectly, I have also identified where I had gone wrong. In re-doing the shimming, I had shimmed the bevel gear too low down/close to the spur gear. While the gears all meshed nicely and turned freely on their own in the gearbox, I am assuming that once the motor was replaced, even at its lowest height, it was jammed onto the bevel gear too tightly and the resistance was too much.

 

I have no idea how or why on my first attempt at disassembling and reassembling I lost the semi-auto function but retained a fully cycling gearbox, as that now works fine also. I think it may have had something to do with putting the trigger back on. When I put it back together just now, it initially was catching somehow on the anti-reversal latch and moving it out of the way by a small amount. I couldn't say for certain however.

 

Next job will be to get some more greace and do that job, now I am happy that I can reassemble the stripped gearbox in a working order (eventually).

 

Thanks for all your help and input guys. Very much appreciated.