Locked gearbox

[Edward McRichy]

Here are the details
Gun: A&K M4 S-system
Battery: 9.6v 1600mah fully charged
Motor: A&K stock motor and matrix 3000 high torque motor
Spring: SP110

Hey guys, need to know if someone has had this problem and was able to solve it, it seems that there could be multiple causes and multiple solutions.  The gear box from my M4 keeps locking up (piston locked back, won't complete cycle), I would have to open up the gun and pull on the anti reversal latch to release the piston, fire again and same thing happens.  I have spent a few hours over the last couple of days looking on the web and through this forum and haven't really found a solid solution that fixes my problem. 

This problem keeps on happening to the gear box, some of the possible solutions i have found online are the following: "use a bigger battery" battery size should not be a problem, "install a high torque motor" as you can see high torque motor is used, "shave off the back of the tappet plate, plate preventing sector gear from completing rotation" haven't tried yet but may some time this week also why would this all of a sudden be the problem, plate looks intact with no visible problems, "gearbox shimmed too tight" without the spring and piston and with all screws tight gears rotate without problems. 

Any suggestions would help out a lot.  I have no problems working on my own guns and opening the gearbox and doing what needs to be done I just can't seem to find a solid solution to this particular problem. 

Thanks

Update:  My locked Gearbox has been fixed, I took it to LynchTec to have him fix it.  I can't remember what all he said he did to it (I was overcome with joy that it worked), he basically gutted the gear box, cleaned it out and put it back together, swapped out a few internal pieces, reshimmed the gears, provided a new high torque motor and cleaned up my wiring.  LynchTec provided excellent service and got my gearbox operational.  If your AEG needs worked on I highly recommend LynchTec....thanks Warlord

[Old Dog]

Could it be that even though your battery seems fully charged it is possibly defective and you are not getting the power you need to complete the cycle, have you thought of trying another charged battery, just my $.02

There are a lot of good techs on AA, Spazz, Nuke plus others with a great store of knowledge...

Good Luck

[SSV Noble]

Have you set the sector gear in the right position to catch the piston teeth in the right sequence?
Also check your gears some teeth could be damaged as well from wear and tear.
Hope some of this could help.

[Exarach]

Have you checked the shimming on the gearbox?
Too tight, and it won't turn.
If yes,
Then it sounds like you have a battery that is not strong enough to turn the motor,
Incorrect motor height,
Backwards wiring on the motor terminals
Perhaps a short in the wiring, that is causing heavy resistance? -Very long shot

I would try with another battery, and, it if turns roughly, redo the shimming, and motor height.
You should do a manual wire check.
It might also be worth swapping in a substitute motor, it is easy enough, and not unheard of for a newer motor to go unexpectedly.

[dannerson]

Other than the motor and spring is everything else stock?

I had a similar issue but I was able to find the issue was related to the shs/core gears were slight larger in diameter / selector gears for the piston rack were slightly larger/wider

[Edward McRichy]

Other than the motor and spring is everything else stock?

I had a similar issue but I was able to find the issue was related to the shs/core gears were slight larger in diameter / selector gears for the piston rack were slightly larger/wider

the gears are stock, piston and cylinder are upgraded but don't know what brand.  when I unlock the box and attempt to shoot I am able to get a few shots off prior to the box locking up.

[Edward McRichy]

Have you checked the shimming on the gearbox?
Too tight, and it won't turn.
If yes,
Then it sounds like you have a battery that is not strong enough to turn the motor,
Incorrect motor height,
Backwards wiring on the motor terminals
Perhaps a short in the wiring, that is causing heavy resistance? -Very long shot

I would try with another battery, and, it if turns roughly, redo the shimming, and motor height.
You should do a manual wire check.
It might also be worth swapping in a substitute motor, it is easy enough, and not unheard of for a newer motor to go unexpectedly.

1. With the spring removed and the gear box put back together the gears turn just fine.
2. Motor turns and engages gears like it should, sometimes i can get off a few shots prior to locking up.
3. double checked wiring, everything good
4. tried three batterys, (two brand new fully charged)
thanks for input

[Bob Z Moose]

Just spitballing here... What about the spring guide?

[Edward McRichy]

Just spitballing here... What about the spring guide?

Didn't think about the spring guide, it's stock.  What problems could i possibly encounter with the guide?

[Bob Z Moose]

Well, you're getting locked up after a few shots after you've worked with it. Not sure (and I'm sure someone will set me straight), but I can just see the spring binding on a guide that is flexing or cracked. Again, just threw that out.

If the motor and electrical system is working normally and it isn't the shimming or the gears, there's very few parts that are left. Maybe something to due with the piston?

[Edward McRichy]

So I spent some time today trying to fix my gear box, no luck, piston still locks back.  One of the common solutions people have brought up is a larger battery.  What size battery should I be using?  As I stated in my original post I'm using a 9.6v shouldn't that be enough to pull back an Sp110 with a high torque motor?

[spazz]

if you are close enough to 19th ave and union hills. you can bring the gun into command post and i will help you look at it and diagnose what could be wrong.  ill let you do all the work of course so that i dont have to charge you anything.
its realy hard to properly diagnose a problem especialy if you dont have the gun in hand and cant look at the parts involved.
but in reading your description of the issue all other things being correct, (shimming and such and no parts being dammaged) is also for the battery. depending on the type of battery and the discharge rate they can be very short lived.

[Dayton]

Have you checked your trigger contacts? They could be severely worn/burnt.

[dannerson]

Does the pinion gear from the motor mesh well/properly to the bevel gear? Being a Matrix / evike motor I've read a few things about them not meshing. Could eliminate this by putting your stock motor in to see if I cycles.
You could also check the bevel gear shimming to pinion if it's to tight that could cause the problem too. I know when I first started I was over shimming a little because I wasn't closing the GB with the screws to check my shimming I was just using my hands to pinch it closed.

Throwing this out there. The other thing to check for is burr on the tappet plate. I'm not sure how stiff the A&K tappet plates are but if they are floppy could be a factor. Flicking up from the selector gear to the piston rack. Stiffer tappet and a selector delay clip.

[Edward McRichy]

Locked gear box fixed, see update in original post.......Thanks to LynchTec (Warlord)