CA m249 Gear box problem

[Pharaoh 6]

Allright. I'm at my wit's end on this one. I have a brand new CA M249 and the gearbox keeps stopping. I can fire one long burst and when I let go of the trigger and then pull it again it won't fire. I can see the gears trying to move,but they won't.

I've had a new piston head put in, new bearings and a M120 spring. I've tried firing it with the stock spring and M120 as well as a 8.4v 1400mAh and a 9.6v 2000mAh. Nothing works. I have to release spring tension by lifting the anti reversal latch. The piston then shoots forward and I can fire again. 1 long or short burst and then it stops.

It has been professionally looked at and shimmed and each time sent back to me working until I touch it. Then nothing.

I'm just posting here for any ideas on what to look for.

Help?

[CalvinB]

not trying to be rude, but how can you see the gears trying to move?

one thing you may want to look at is the trigger switch those switches are notorious for epic fail. the other thing is if you are cracking the gearbox open yourself, one thing I've noticed with my own MG gearbox is that the tappet plate can pop off its track right before you slap it shut and that will make the spring cock back but not allow it was go forward. I don't know if that's your issue or not but those are good places to start with an MG style gearbox (AKA the brick)

[league 4]

not trying to be rude, but how can you see the gears trying to move?

one thing you may want to look at is the trigger switch those switches are notorious for epic fail. the other thing is if you are cracking the gearbox open yourself, one thing I've noticed with my own MG gearbox is that the tappet plate can pop off its track right before you slap it shut and that will make the spring cock back but not allow it was go forward. I don't know if that's your issue or not but those are good places to start with an MG style gearbox (AKA the brick)

The spur gear sticks out the bottom so he can probably see it rotating. What bearings were put in? Are you sure they were correct 8mm M249 bearings?

[rockettravis]

not trying to be rude, but how can you see the gears trying to move?

one thing you may want to look at is the trigger switch those switches are notorious for epic fail. the other thing is if you are cracking the gearbox open yourself, one thing I've noticed with my own MG gearbox is that the tappet plate can pop off its track right before you slap it shut and that will make the spring cock back but not allow it was go forward. I don't know if that's your issue or not but those are good places to start with an MG style gearbox (AKA the brick)

My money says nesta is right.

[Pharaoh 6]

League 4 is right. I have the gear box out and can see the gears moving from the bottom. It's not the switch or the tappet plate. Both of those are moving correctly. It's either the piston getting stuck or a problem with the motor not wanting to work right. The gears from what I can tell were shimmed correctly. All the spacing looks good, so they're not binding up.

Before I go and start randomly replacing parts I just wanted some feedback and to see if anyone else has ever had the same issue.

[demmon]

Quick question, do you have a ball bearing spring guide? Mine reacted similiarly and it was the piston sticking on the guide. I also had an issue briefly due to the trigger aligning with the switch. A couple thoughts....

[X]

Who worked on it last? When all else fails and you just can't do no more . Take it to Shogun .Nuf said problem solved .
You can try to go it with all the good hearted guys you want but this guy will end your grief hands down and he stands behind his work . Just a thought.

[CalvinB]

Who worked on it last? When all else fails and you just can't do no more . Take it to Shogun .Nuf said problem solved .
You can try to go it with all the good hearted guys you want but this guy will end your grief hands down and he stands behind his work . Just a thought.

I 100% agree, Shogun taught me everything I know about teching airsoft guns and I've gotten to know quite a bit and I know about 5% of what he knows. The only problem is that last I heard he is out of commission since the PDX store closed, CommieHunter knows his stuff too. I would say the only difference is that Shogun just has to look at the gun hard enough and It will fix itself out of fear, Whereas CommieHunter has to get out his tools to threaten it with something before it fixes itself.

[Ash]

Shogun is still working for ASONW, which now only has the Cornelius store. Shogun by far one of the best techs in this area I would highly reconmend him. If you need to get a hold of him you can either PM him or call ASONW at 503 992 1092.

[CalvinB]

good to know, I was worried about how the schedules would work out. Final word, go to AONW between CommieHunter and Shogun it'll work better than ever.

[Pharaoh 6]

Hey everyone thank you for all the ideas. I'm pretty sure I figured out what is wrong now I need to figure out how to fix it.

Demmon looks like he was correct. From what I can tell the gear box always stops in the same part of it's cycle...when the piston is almost fully back. Back far enough that I can see it towards the rear when looking from the bottom of the box, but not far enough back for the spur gear to hit the untoothed part and release the piston.

It looks like the piston is sticking on something.

Any ideas on what and how to fix it?

What is a ball bearing spring guide and where do I get one?

Thanks again.

P6

[CalvinB]

BB spring guides are this: http://airsoftoutletnw.com/index.php/Ai ... de-V2.html

it has a ball bearing plate that allows the spring to twist as it compresses and releases which makes it easier for the motor to pull the spring back and for it to fire. They come in handy on high speed or high fps guns but are a good upgrade for all guns. If your motor sounds like it is struggling i would also get piston head with BB's, it does the same thing that the spring guide does for the back of the spring, for the front. On top of extended lifespan of the motor, gears and piston (which you not only want but need in an MG) you will probably gain like 2 RPM and an FPS

to check if it sticking, crack open the gearbox and pull out the spring, spring guide, sector gear, and the cylinder assembly and run the piston back and forth on the piston track and feel for if it sticks, find out where it sticks, on both halves of the case. Once you know where it sticks look and see if there are any thick spots or burs or anything and if there are, gently and slowly sand down those areas. Keep in mind that both the width and height of the track can cause it to stick. Also lube is your friend, white lithium grease the track and the groove on the piston.

doing both of those should get you squared away

[shogun]

is your spring in backwards?

i know its a silly question but stock springs are usually evenly pitched(IE the coils are evenly spaced all the way through the spring) and most after market springs are differentially pitched(IE tighter coils on one end tighter coils in the middle and more spaced coils o the other end.

The proper way to install an irregular pitch spring is with the tight coils on the spring guide. having the spring the other way can change the load during different parts of the gear cycle and can cause the box to lock up like you describe.

it wont always happen depending on your motor/battery setup, but its worth checking, and a lot of people miss this.

[firemedic2296]

We had a similar problem with CA M4, we had to loosen the motor to get it unbound, I have adjusted the motor height and it hasn't done it since? not sure if that if its the cure, but it seems to have helped. just a thought.

[FPDoc]

If the sector gear is shimmed too high it could be periodically binding the tappet plate. There's a lot of travel room for the spring and piston so Id be surprised if the spring guide was holding it up.