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Synastr

gearbox locking up on full auto

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ok so I picked up this jg cqbr gun that im toying around with. well it has a m120 spring, metallic red endbell jg m93 motor. im using a 7.4 2000 mah lipo. semi works fine. no lock ups shoots fine. if you shoot full auto then stop it will lock up somewhere between half compression and full. ive reshimmed it, checked motor height. I cannot figure out what would cause this. the internals are all factory and it never use to do it. so what are some cause of this and what should I change to remedy it.

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yes factory piston, I either unlock it with the arl. or I pop it with my rc 11.1 lipo. as for battery its a turnigy nano tech 7.4 2000 mah 20c battery. ive somewhat checked the piston rails, it seems to slide just like every other gearbox ive worked on. ive even tried a different motor. it seems like it has binding in the cycle. but I cant seem to find it. maybe one of the gears is bad? bent shaft. ill have it opened back up tonight to inspect it again. its just odd that semi works perfectly fine, full cycle. no lock ups. but when you do a full auto burst it locks up wherever the piston is when you disengage the trigger.

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no its not battery. believe me a 7.4 lipo would easily turn this gun over as well as any other. and my 11.1 is a huge discharge battery. 5800 mah 50c 11.1 so ya itll turn over just about anything. my battery is not the problem. its new, been cycled properly, as well as works my ak perfect which is pulling a m140 spring.

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im sorry but are you guys even reading the posts? I said I tried a different motor. nothing changed. well it cycled slower because it was more of a high torque. ive tried the 11.1 on full auto. it will still try to lock up. even though it has tons of amps being pushed. the only thing I can think is that its something with the gears. ill take it apart tonight and sand, smooth, shim, and grease everything again and make sure its all good. then ill try my jg blue motor that I know works flawlessly and see what happens. if it still locks up, I wont know what to do.

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maybe the spring is bunching up inside the piston when it pull back. one or more of your coils may be out of place

 

I think its odd that a more powerful battery fixes it. just because your 7.4 runs the other gun nicely does not mean that it will run another gun the same way. its not going to be like plugging an 11.1 lipo into any gun ever

Edited by Zemanova

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The 11.1 doesn't really fix it. It just can unlock it. For it to be an 11.1 it shoots very slow anyway. I know something's binding. See if you run a plain cheap motor. The 7.4 won't move it and the wires get hot. And the 11.1 only pulls it back one or two times then locks up. I could almost swear something's binding because on semi. It drags into the shot. Almost like using an 8.4 nimh. I'll update with progress. I might try a different piston and piston head. Possibly spring. To see if it clears up.

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The 11.1 doesn't really fix it. It just can unlock it. For it to be an 11.1 it shoots very slow anyway. I know something's binding. See if you run a plain cheap motor. The 7.4 won't move it and the wires get hot. And the 11.1 only pulls it back one or two times then locks up. I could almost swear something's binding because on semi. It drags into the shot. Almost like using an 8.4 nimh. I'll update with progress. I might try a different piston and piston head. Possibly spring. To see if it clears up.

 

 

To be honest, if a gun can semi shoot but lockup in full auto, I would assume there is an electrical cut-off. If the gearbox can't cycle it should be locking in semi too. The trigger isn't cutting off is it? What fuse protection are you running?

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running a 40 amp fuse. and it doesnt cut off the electrical. because you can hear it trying to move the piston. its so weird. its like once the piston is halfway back, semi wont pull it. but once it starts from the beginning it can. I don't know whats wrong. im going to tackle it tomorrow and redo anything inside. polish some stuff. correct stuff. then ill see what it does.

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Sounds to me like the motor is not strong enough, if the spring is non-linear it would make sense the motor can pull the spring when its uncompressed but not when it is already a little bit compressed (half through the cycle). But it is probably a shimming issue as IIRC the JG Red is actually a pretty decent motor and should have no problem with a m120 on 18:1 gears.

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running a 40 amp fuse. and it doesnt cut off the electrical. because you can hear it trying to move the piston. its so weird. its like once the piston is halfway back, semi wont pull it. but once it starts from the beginning it can. I don't know whats wrong. im going to tackle it tomorrow and redo anything inside. polish some stuff. correct stuff. then ill see what it does.

 

So if I understand correctly... it will lock up if in the middle of the cycle? Full auto won't lock up immediately but during full auto you create a chance to lock up by leaving the gearbox mid cycled?

 

Just check all gears for resistance with all parts... cut-off, tappet plate, both sides of the gearbox, the piston, make sure the piston can cycle all the way back by hand with no resistance. All gears need at least .05~.1mm of movable space to move efficiently.

 

If that is all checked I would suspect the wiring and battery next. Is this a 40 amp polyfuse or regular 40 amp fuse?

 

 

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well I cracked it open. sanded some moving parts lightly. reshimmed it with a tad bit a play so I know theres no resistence. checked wiring. checked aoe. I added some mouse pad foam to it. shaved two teeth of the piston. regreased it. put it together. now it seems ok. hasnt locked up yet. only thing im wondering now, is why the jg red motor seems slower than the jg blue. im so lost. I think ill buy a shs motor and be done with it.

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I find this really interesting, last night I upgraded my echo 1 stag-15 with a m110 spring, madbull px piston-02 (full teeth) and a G&P piston head, got everything back together made sure that that my gears were shimmed properly and lubed. I installed the motor (stock motor) and when I pulled the trigger and the piston locked up. I tore it all down again rechecked for binding and lube. Put it back together again this time it fire several times and then it locked up. I then realized that I hadn't charged my battery after I last used it (8.4) it was late so I just put it on the charger this morning and then going to try again. I am hoping that it was just a weak battery otherwise I am in the same boat. I don't want to shave any teeth as the piston is metal teeth....

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I find this really interesting, last night I upgraded my echo 1 stag-15 with a m110 spring, madbull px piston-02 (full teeth) and a G&P piston head, got everything back together made sure that that my gears were shimmed properly and lubed. I installed the motor (stock motor) and when I pulled the trigger and the piston locked up. I tore it all down again rechecked for binding and lube. Put it back together again this time it fire several times and then it locked up. I then realized that I hadn't charged my battery after I last used it (8.4) it was late so I just put it on the charger this morning and then going to try again. I am hoping that it was just a weak battery otherwise I am in the same boat. I don't want to shave any teeth as the piston is metal teeth....

 

 

so I was able to figure out the issue in my case, turns out the stock bearings were toast, in fact this time when we opened up the gearbox one of the bearings exploded. They were 8mm roller bearings, so I ordered steel bushings to replace them, hopefully this wil fix the issue!!

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I had a similar issue with an SRC G36 GB. It seemed to be piston fitment. Some pistons would somehow allow the sector to push it up into the rails and somehow bind. Finding the right piston fixed it. Perhaps this thread would be useful to you.

 

On another V2 GB it appeared to lock up too. What the problem was with it is that sometimes the trigger sear would slip under the trigger trolly and although the trigger was pulled the trolly was not engaging the contacts. In this case the motor would not be connecting to the battery during the lock up so it is probably not your problem.

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so I was able to figure out the issue in my case, turns out the stock bearings were toast, in fact this time when we opened up the gearbox one of the bearings exploded. They were 8mm roller bearings, so I ordered steel bushings to replace them, hopefully this wil fix the issue!!

you should get the bearing bushings that have the shields on them. I don't trust the open bearings AT ALL.

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ive been having the same problem, I put the gearbox together, fire semi and its fine nothing locks up, when I go to full auto I pull the trigger and it fires but when I release and pull trigger again, piston pulls back but doesnt release. I am going to give my gears a little play for the shimming, there is no play at all right now, and they spin fine

my parts list:

https://www.evike.com/products/91804/

https://www.evike.com/products/10296/

https://www.evike.com/products/28692/

https://www.evike.com/products/27740/

https://www.evike.com/products/86953/

https://www.evike.com/products/38479/

https://www.evike.com/products/32915/

https://www.evike.com/products/46105/

https://www.evike.com/products/86964/

https://www.evike.com/products/62385/

https://www.evike.com/products/38464/

https://www.evike.com/products/30997/

https://www.evike.com/products/31456/

stock vfc trigger, safety, tappet plate

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Bad battery...and over priced.

O-ring nozzles are a gimmick...Fluid Dynamics prove you don't need an O-ring nozzle for compression.

Another issue is your mixing  a lot of varied parts.  

The Days of TM compatible are 14 years past.

It would have been more economical and getting a complete ACM mechbox for 45.00 and just replacing the few "weak" pieces.

What spring rate did you get?

Edited by Guges Mk3

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On 6/26/2020 at 4:27 PM, Guges Mk3 said:

Bad battery...and over priced.

O-ring nozzles are a gimmick...Fluid Dynamics prove you don't need an O-ring nozzle for compression.

Another issue is your mixing  a lot of varied parts.  

The Days of TM compatible are 14 years past.

It would have been more economical and getting a complete ACM mechbox for 45.00 and just replacing the few "weak" pieces.

What spring rate did you get?

M115 spring. I've got 3 nimh 9.6v batteries and it locks up on full auto using each one. When I look inside the gears are 3/4 through the cycle and It goes back fine when I turn the gears. I've check my aoe, motor height, shimming, and it still locks on full auto. A few months ago I had a different gearbox shell and it all ran smooth no issues, but it was too tight of a fit in my lower receiver where the selector switch was very stiff and wouldn't seat low enough as the stock shell would (vfc scar H) I'm going to try a the stock gears again and see what happens

 

http://imgur.com/gallery/RnzoyOo

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I tried it

4 hours ago, BillStrachan said:

M115 spring. I've got 3 nimh 9.6v batteries and it locks up on full auto using each one. When I look inside the gears are 3/4 through the cycle and It goes back fine when I turn the gears. I've check my aoe, motor height, shimming, and it still locks on full auto. A few months ago I had a different gearbox shell and it all ran smooth no issues, but it was too tight of a fit in my lower receiver where the selector switch was very stiff and wouldn't seat low enough as the stock shell would (vfc scar H) I'm going to try a the stock gears again and see what happens

 

http://imgur.com/gallery/RnzoyOo

I tried the stock gears and got the same problem, it's gotta be the piston that's the issue, I've tried 3 sets of gears, unless it could possibly be incorrect shimming for the bevel gear? This is very frustrating. Update: I pulled out the spring after the cycle got stuck and I think I may have found a potential problem, the bearing covers for the spring guide prevent the piston from going back further, I believe this is the problem I've been having, my best option would probably be to take off 1 or 2 teeth off the sector gear? I'm not familiar with doing this so if there are any other options please let me know

Edited by BillStrachan

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Bearing spring guides are not needed.  

You are not running a double bearing system are you?  One at piston head and one at spring guide.  You actually don't need any bearings at all.  You just need a slider in the form of a washer on the spring guide.

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12 hours ago, Guges Mk3 said:

Bearing spring guides are not needed.  

You are not running a double bearing system are you?  One at piston head and one at spring guide.  You actually don't need any bearings at all.  You just need a slider in the form of a washer on the spring guide.

Yeah I am running a double bearing system, if I shouldn't do that then I will just use the stock plastic piece no big deal

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Double Bearing system is beyond redundant.  It's actually stressing your mechbox more than normal and is contributing to mechbox lockup.

Spring is bottoming out.  This can cause the issue you are having with along with the bearing not consistently fitting into the piston.

Spring is operating at a higher spring rate due to 2cm of precompression.  Makes your motor work harder...etc...

Causes a higher FPS than anticipated.

Can lead to mechbox failure, common with V2 and in the cold.

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9 hours ago, Guges Mk3 said:

Double Bearing system is beyond redundant.  It's actually stressing your mechbox more than normal and is contributing to mechbox lockup.

Spring is bottoming out.  This can cause the issue you are having with along with the bearing not consistently fitting into the piston.

Spring is operating at a higher spring rate due to 2cm of precompression.  Makes your motor work harder...etc...

Causes a higher FPS than anticipated.

Can lead to mechbox failure, common with V2 and in the cold.

So by removing the bearings for the spring to sit on, this will fix my issue?

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Unknown..you provided no pictures for comparison or examination with your issue.  If we can't see it we can't definitely say.  

I would say remove the bearings on the spring guide and inspect and test component compatibility before you put the box back together.

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On 7/1/2020 at 10:48 AM, Guges Mk3 said:

Unknown..you provided no pictures for comparison or examination with your issue.  If we can't see it we can't definitely say.  

I would say remove the bearings on the spring guide and inspect and test component compatibility before you put the box back together.

I'm unable to take the bearings off the spring guide, all the parts I try together still lock up. Whenever I open the gearbox back up after it locks up, the gears are mid cycle of pulling back the piston but for some strange reason it doesn't want to it back after a certain point, it's like it refuses to.  I've tried different piston with different gears but it still locks up

https://imgur.com/gallery/y52g4Qx

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Due to the de-evolution of modern airsoft parts.  Any of these could be your issue.

Gear Box rails are not consistent and too high at back of mechbox.

Piston guide rails are too thick and bind on mechbox guide rails.

^The above two issues can be exacerbated if they both exist.

Spring is too long, or of an inferior design and is bottoming out preventing piston from moving back.

Motor is of a low quality and can't wind the spring back, exacerbated buy a redundant double bearing system.

Battery is of a low quality or performance level that can't supply the "AMPS" to turn over the mechbox for a complete cycle.

Piston is not cupping over spring guide due to flex in gear box channel.
 

Edited by Guges Mk3

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