Gearbox repeatedly jamming

Avose

I'm using a SRC M4 and a 8.4v 1250MaH NiMh, and frustratingly my gearbox keeps on locking up.

For a while i assumed it was my battery and planned on getting a new one, but i then swapped batteries with a friend. Both batteries were fully charged. My gun still locked up after less than 50 shots, while his gun (using my battery) worked perfectly for the entire day going through roughly 1000 BBs, maybe slightly more.

After researching on the internet I saw that there were so many possibilities of what it might be... some people even said that it could just be the height adjustment of my motor.
But it seems thats not it either as ive adjusted the motor several times and the problem still persists :mad:
I used to have a problem where the motor was firing inconsistently, so i was told to tighten the hex, then this problem started happening. But it still seems to be locking up even when I loosen the hex on the pistol grip.

I'm really hoping i can get answers from experienced airsofters here. I would be willing to (but would prefer not to have to) buy a completely new gearbox and motor.

If you need any information (pics, vids, etc.) just ask and ill get them up.

P.s. I just finished unjamming the gearbox as even a fully charged 9.6v wouldn't push it over the cycle. Had to open it all up.

NakedDex

This is actually a really easy fix; get a bigger battery. I'm not kidding, it's that simple.

What's happening is that the battery can't supply enough power to overcome the spring compression completely. It has enough to put a small amount of compression on, which allows the bevel gear to turn a fraction of a revolution before the spring overpowers the piston and tries to force it back. This fraction of movement is enough to engage the anti-reversal latch on the bevel gear and lock the whole box.
To overcome it, simply use a decent 9.6V pack instead. Your battery packs are actually fine, they're just underpowered for your rifle. I've seen it happen on many rifles, including one of my own.

An alternative fix is to buy a high-torque motor (rather than high-speed). These are able to produce that bit more compression on the piston with less power, but you'd really need to be pairing these with a higher voltage pack to get the most out of it.

If you really wanted to go all out, fit (or have one fitted for you) a MOSFET and throw in an 11.1V LiPo. You'll certainly never experience that problem again, and you'll benefit from increased rate of fire and faster trigger response. Again, couple this with a high-speed (not high-torque in this case) motor for maximum effect.

Avose

Could i buy a high speed motor (i really want the G&P m120 high speed) and couple it with a 9.6v? i would prefer speed than torque, but i dont think i would have enough cash for lipo, mosfet and a new lipo smart charger.

Also are you SURE its the battery? I was told (by an airsoft retailer) that SRC usually have a high torque motor in my gun, and when they arrive in ireland they just downgrade the spring.
plus my batteries seem to work fine in 2 of my friends guns, yet their batteries don't work in my rifle. Are you saying all/any 8.4 batteries are too weak for my gun?

Private Snafu

Did the batteries work in the gun before?
Have you opened the gearbox yourself to work on it?

NakedDex

Yeah, your battery packs are fine. They'd probably work fine in 90% of other guns you'd put them in. If you had a decent 9.6V pack to hand, it'd probably work fine on just that. The problem is simply that your gearbox can't run on the power provided by the 8.4V pack. There's a whole complicated explanation that involves discharge rates and power capacities, torque/speed graphs etc, but the jist of it is the battery just doesn't have enough juice to force the piston back the full rack length, so it's getting stuck at some point in the middle of the cycle.

The problem with high speed motors, which most people in Ireland seem to be oblivious to, is that a motor can either have a high torque, or a high speed. If you want one, you sacrifice the other. High torque motors, consequently, don't tend to run particularly fast (although you'd only notice the difference on a chrono-ROF test). They do have better starting characteristics though, which is what you're really after here.
Some (less quality) high torque motors do draw more power though, so it's possible that a decent 9.6V pack (NiMH preferably, they have a higher discharge rate than NiCd) coupled with a decent high speed motor (the M120 is a good choice, TM EG1000/3000 are also great choices) could be enough to get you up and running.

Certainly, if you want an M120 anyway, go for it and test it with a 9.6V pack. Worst case scenario, it doesn't work and you start looking at LiPo, with a headstart on your set up since you have the motor.



Also, there's a massive set of alarm bells ringing around what that retailer, whoever they were, told you. I'm not sure about SRC having high torque motors, I haven't seen the new generation ones to know for sure whether they do or not, but this...

when they arrive in ireland they just downgrade the spring

...isn't something I'd ever want to hear my retailer saying to me.

Avose

yes the My batteries have worked-ish but never to the standard i see in my friends guns. I even bought myself a intellect 9.6v batt but it seems it was a dud as it doesnt work. it never really worked, but i bought it back in august in hobbyairsoft so i doubt they would replace it for free anymore :P

i have never opened the gearbox. Are you sure my gearbox is fine? because it has never sounded as smooth as either of my mates guns... but i guess take this one step at a time.

So you say the motor i want is good, but what brand of battery do you advise? i have a 9.6v intellect but that didnt seem to go too well for me last time >.<
I have heard though that intellect are very good usually, and it would be handy as i wouldnt have to get it posted - theyre in hobbyairsoft which is really close to me.

as for the motor, can i get this in shops in ireland, or do i have to search google for one to be shipped?

NakedDex

Battery brand really doesn't matter. Strip the heatshrink off the cells and you'll find the vast majority of battery packs you own are made up of Sanyo cells anyway, so it makes no difference whether it's Intellect, Firefox or anyone else. It's like that Toyota Aygo a few years ago. The Citroen C1 and Peugeot 106 were actually the same car, made the same factory, made somewhere in east Europe (country escapes me right now), but with different badges applied.


There's always a chance you got a dodgy pack. Before you go investing in a whole new raft of batteries, borrow someone else's and try that. If that works, but not as well as you'd like, buy and fit the new motor. If it doesn't work, have a gander at LiPo.

HOWEVER, before you go making any mods to the gun with new motors or LiPo's or whatnot, have a chat with the retailer you bought the gun from. If it still won't run on a 9.6V pack, the retailer should really offer to take a look at it. Despite what some brands claim, I've only seen a handful of rifles that were genuinely "LiPo ready", and even they could run smoothly on 9.6V.


If the gun isn't running smoothly, that's possibly a sign of a bigger problem. Honestly, without hearing it in person, there's not a lot I could do to diagnose that. It's probably that it's not running as smooth simply because it's running slower, struggling with the spring. It's hard to determine from here though. Unless you know what you're doing, I wouldn't open the gearbox.

If you're convinced the gearbox has issues though, I'd bring it back to the retailer (assuming it's reasonably new and within warranty). How long have you actually had this rifle?

Avose

Well i bought this yolk secondhand off a guy on boards in August, and he had it for a while before me... so its kinda old :P Definatly not in waranty cause they olny last a couple of months right? I still have a sticker on my gearbox prooving its from MIA. and i havnt opened the gearbox ("warranty void if removed" sticker)

I looked the part no. on the box and its quite an old generation
Could the gearbox just be gettin elderly?

Could i try show you my problem on video? cause i rarely ever get to go to airsoft shops. I have no means to get there as my parents wont drive me and i dont have a car.
Ill still try go if you think its best, but it might be something simple and as soon as you see it youll just go "Oh its so simple! Happened to a friend of mine actually, all you have to do is.....and then it will work BETTER than most new guns."

Okay you probably cant do that but you might be able to help a little.
I dont mind dirty work with the gearbox btw, i love all that kinda stuff. Ive opened all my gadgets to date, usually to fix them. Ipods, iphones, psps, laptops that kinda stuff. And bought broken scorpion and fixed that too.
all i would need is directions. I usually just try find a vid explaining wtf to do, but i couldnt this time which is why i came here.

Thanks
Avose

NakedDex

It's not "elderly" per se, but older generation SRC's (Gen 1 or 2) never had great reliability.

Whether you open it or not is up to you, but once a gearbox is open, any fault finding becomes a purely visual process, so you're sort of on your own. That's why I suggested having someone with experience do it for you.
A gearbox is very different to opening an electronic device. There's tolerances and positioning to account for, as well as dealing with compressed components with springs.

If you're not happy with it and you think you can do it, go for it. However, Occams Razor applies heavily in airsoft. Don't go looking for a problem in the gearbox that could just as easily be caused outside it, where fault finding is easier. Start at the easiest, most accessible component that could be causing the problem (battery/motor) and work your way to the most technical and difficult to access (gear teeth/piston rack).
Starting inside the box for a problem like this doesn't make sense, especially if the only part you'd need to purchase to test the most likely fail points (the M120 motor) is something you intend on buying anyway. The simple solutions are usually the most effective.

Avose

okay great ill order myself one of the G&P motors along with a 9.6v

Is there anywhere local (as in in Ireland) that supplies these motors do you know? postage from sites in hong kong (ehobbyasia.com) and america (evike.com) are usually so much

And also thanks alot man you have been such a massive help. without you i probably would have meddled with (and ruined) my gearbox. really helpful.

Thanks,
Avose

Damo 2k9

Try hobby airsoft, they have a thread here on boards and I think they have the motors in stock

glicster

just an idea lads,he says its an old gun so could there be the possability that the trigger contacts are burnt and when the gun stops mid cycle the contacts arent letting enough power to the motor to overcome the resistance from the spring?

clubberlang12

Before you go spending €30+ on a new battery and similiar on a new motor would you not try and get someone to have a look at the gun. You've said that your mates fully charged 9.6v was still encountering the same problem so who's to say its battery related. You've said you haven't opened up the gearbox yet so it could be a number of things that could be happening inside there. Put up your location here and see if there is anyone close by that is experienced with repairing guns. I'm sure they wont charge much, if any at all, and at least then you'll know what is the cause of the problem without spending money on something that may not be the solution.

DeBurca

As you say the gearbox has an MIA ("warranty void if removed" sticker) there is a possibility that it has been downgraded by the drill a hole in cylinder method, check the cylinder to see if there is a small hole drilled in the brass cylinder wall
If this is the case then it still has the original spring which would be rated at about 1.4 Joule
So the motor has to compress a stronger spring which is placing an undue load on the motor/battery combo

NakedDex

This is something I considered too, but I was under the impression such ridiculous methods were a thing of the past.
Definitely check this before proceeding. It was remiss of me to dismiss it.

Avose

wait so where do i find the hole? under the sticker? do i have to open up the gearbox to find it?

also if this is the problem how would i go about fixing it? new spring obviously, but then do i need a new gearbox shell?

EDIT : im just after checking it, and without taking apart the gearbox, i can see no holes.

glicster

Avose wrote: »

wait so where do i find the hole? under the sticker? do i have to open up the gearbox to find it?

also if this is the problem how would i go about fixing it? new spring obviously, but then do i need a new gearbox shell?

no lad,just look at the cylinder and you should see it,it should be near the front. wont need new gearbox just cylinder,spring and maybe piston/cylinder head depending if any damage has been caused by little pieces left from drilling.
but if this scenerio is to be true,and gun worked fine untill recentlly,theres still something else wrong for it to start happening in the first place

but to fix the lock up do as dex said,bigger battery,but you still need to find the cause

DeBurca

As Glicster said if the cylinder is drilled it should be visiable unless the cylinder has been turned after drilling
Also check the Air-nozzle to see if it could have been also drilled
I have attached a few photos of the sort of thing I am talking about

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Avose

uhm okay... really newbie question here now... what is the cylinder? i always thought i had to open the gearbox to see it. its what pushes the air out right? wont the air nozel at the front be in my way?

edit ; just saw the pics post, and no there are none of the holes, unless like glicster said the cylinder was turned.

Edit 2 : Crap.... okay i just looked close. there is a hole and i have a pic.

dammit... what do I have to go and buy now? new spring, and then ....?

Thanks,
Avose

DeBurca

You will need to replace the Cylinder and fit a proper spring like the original Retailer should have done in the first place
But your problems may not stop there as the BURR generated inside the cylinder wall from drilling the hole will have damaged the O-ring on the piston head and there is also a good chance that the piston head itself may also be damaged

As you will need to do the above can I suggest that as the gearbox is open you take the time to shim the box and if it does not have metal bushings that you fit them also

Avose

What is the BURR?

Okay so now whats on the new parts list?

New cyclinder,
m100 spring,
piston head and o-ring,

do i need the motor and 9.6v batt anymore?

edit : ok lads ive been lookin on ehobbyasia (i really wanna buy from here as its cheap and so is postage) for cylinders and piston heads etc, and i havnt a clue what brand to buy... Any advise on good parts? i really havnt a clue what the difference between any of them is...

thanks
avose

DeBurca

A burr is the name given to the rough surface left as a drill goes through metal

Yes a new cylinder and I would suggest an M90 spring and it should give you 310ish PFS
A new piston head comes with an O-ring fitted, I prefer to use a Bearing Piston head on all my repairs/rebuilds

I would hold off on the Battery and the Motor until the repairs are complete
You will also see a ROF increase due to the reduced load of a lighter spring

glicster

dude if you have the cash handy for all these parts can i reccomend something,try get the gun to someone who knows what there doing and pay them.theres a lot of things that might need replacing and for someone who hasnt done it before theres a big chance of something going wrong.
atleast if you give it to someone your guarenteed to get a perfectly working aeg back

i know this is a good chance for you to learn how to fix a gearbox but it could be out of action for a long time if you go it alone

glicster

DeBurca wrote: »

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man thats ugly!

DeBurca

Yes it is and it is thanks to a well known Retailer who likes to put their stickers on gearboxes

AirsoftEire.com

If you want a cheap fix without replacing the cylinder, you can take the cylinder out, file down the inside of the burred section smoothening it out, and then tape over the hole on the outside of the cylinder with a stong adhesive tape. You could also just replace the O-ring on the cylinder head and not the head itself, its unlikely the head was damaged. Drilled cylinders are a curse.

Assuming the gearbox is well sealed, an M90 from a good brand will produce about 305fps and you should then be able to use your 1250mAh battery no problem. While you have the gearbox open, make sure it isn't shimmed too tightly either as this can cause lock-ups.

Decoy

DeBurca wrote: »

Yes it is and it is thanks to a well known Retailer who likes to put their stickers on gearboxes

Apologies for going off-topic but before this turns into a complete sh!tstorm it should be said that there is more than one retailer using this method of 'downgrading'. I will be the first to accept that the most appropriate method is to install a replacement spring but many retailers don't do this, especially on low-/mid-range AEGs.

Avose

glicster wrote: »

dude if you have the cash handy for all these parts can i reccomend something,try get the gun to someone who knows what there doing and pay them.theres a lot of things that might need replacing and for someone who hasnt done it before theres a big chance of something going wrong.
atleast if you give it to someone your guarenteed to get a perfectly working aeg back

i know this is a good chance for you to learn how to fix a gearbox but it could be out of action for a long time if you go it alone

Honestly i dont have alot of cash lying around, probs like 70 ish. I would like to do it myself cause i could save money, but gearboxes are so damn fiddly... i really want to learn how to upgrade and fix these guns, yet i dont want to screw it up. i think with the right advise i could do it.

NakedDex

Decoy wrote: »

Apologies for going off-topic but before this turns into a complete sh!tstorm it should be said that there is more than one retailer using this method of 'downgrading'. I will be the first to accept that the most appropriate method is to install a replacement spring but many retailers don't do this, especially on low-/mid-range AEGs.

Correction: more than one retailer did do it. That's why I neglected to consider it originally. The thought occurred to me, but virtually every retailer has since realised the massive drawbacks and reliability issues this causes. I was under the impression that this practice was a thing of the past, but I'm clearly mistaken.
Also, I've rarely heard of a retailer needing to replace springs in a high end rifle as they're readily available in 1J forms.

glicster

Avose wrote: »

Honestly i dont have alot of cash lying around, probs like 70 ish. I would like to do it myself cause i could save money, but gearboxes are so damn fiddly... i really want to learn how to upgrade and fix these guns, yet i dont want to screw it up. i think with the right advise i could do it.

youtube,mechbox.com as a guide and boards for asking questions.

just so it all runs smothly dont let the gearbox fly apart when opening it and you should be fine,take fotos aswell so you know where everything belongs

also watch out for tiny little washers(shim,s) and make sure if they come off they go back on the gear they came off

Avose

thanks for all the replies lads youve all been a huge help! ill order my parts really soon, and if i have any cash to spare ill buy the battery n motor anyways. Thanks for the link to mechbox.com too, its really clear and helpful. Disassembly doesnt look too bad tbh.

I only have one problem now.... I know what parts to buy, but there are so many different brands and models, how do i know what to choose?

What piston head would you guys recommend,
And what cylinder would you guys recommend?

do i need a new cylinder head?

also does it matter what brand of spring i buy? i mean if theyre M90 then theyre all gonna be about the same power right?

Thanks alot again,
Avose