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deserterghost

Motor can't spin gears, clicking noise.

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About 5 years ago I bought a relatively cheap DBoys KLS RK-01 (AKS74U) gun and after a few years it stopped working.

It had a clicking noise and it didn't shoot. I bought a better battery but it didn't really solve the problem.

I disassembled the gearbox and saw that one of the plastic bushings was broken. I also saw that the piston's plastic teeth were a bit damaged but it didn't seem very serious. (just a little plastic peeled off) I replaced the broken bushing with a modified lego (yes, LEGO) piece and it really worked like it was just a normal bushing. (I didn't want to waste money yet)

I removed the spring and the mechanics worked perfectly. With the spring the motor can only rarely shoot about three rounds when I manually release the anti reversal latch.

 

Except the battery every single part is the original one just as it came out of the factory, and only the mentioned parts seem to be damaged (piston and bushes).

 

My questions are the following:
- Could the motor become suddenly not strong enough, even though I barely shot a hundred rounds?

- Should I buy a new motor, or is it possible that I just need a new piston or something like that?

 

(I will buy new, metal bushes, but I want to order everything at once.)

 

Sorry for the long text but I tried to be as accurate as possible.

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Frankly, I'd be inclined to get a new gearbox altogether, since they can be had for less than 40 quid off ebay and even less if you go to somewhere like ehobbyasia (assuming they have em in stock). That way you'd be sure everything was good to go. You know the gears are a bit iffy on your present set up, and have a bit of a Heath Robinson repair already, which means that sticking a new motor alone into the thing might not solve the problem and probably wouldn't be that much cheaper than just replacing the entire gearbox anyway.

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Chock, thank your for the advice, but I live in Hungary and shipping costs loads of money unfortunately. Otherwise it's not a bad idea to get a whole new gearbox.

 

By the way... can a motor suddenly become not strong enough? I mean I barely used the gun.

Please say that it's all just the fault of the low-end plastic piston and bushings! :P

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I'd be surprised if it was the motor, but its a possibility. Equally it could be the trigger contacts or battery connector has some wear resulting in poor electrical contact, it would be worth checking them as it costs nothing to do so.

 

Bushings come in different sizes (older guns generally have 6mm bushings, newer ones generally are 8mm so you'll need to check if you replace them.

 

But as Chock says the only surefire way of sorting it first time is a new gearbox.

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What would shipping be like from Poland though? Taiwangun have complete gearboxes: http://www.taiwangun.com/en/gearbox-set-v-3-cm?from=listing&campaign-id=20

 

Thanks for the tip, but the shipping would cost 8 euros and the gearboxes are too expensive on this webpage. It would even be cheaper (or the same price) to buy every single part separately. I checked for gearboxes in my country but I couldn't really find this type.

 

 

I'd be surprised if it was the motor, but its a possibility. Equally it could be the trigger contacts or battery connector has some wear resulting in poor electrical contact, it would be worth checking them as it costs nothing to do so.

 

Bushings come in different sizes (older guns generally have 6mm bushings, newer ones generally are 8mm so you'll need to check if you replace them.

 

But as Chock says the only surefire way of sorting it first time is a new gearbox.

 

I'll check the trigger contacts. Although I don't know what it should look like. I hope I'll figure it out.

By the way I have 7mm bushings. (if it's the diameter of the smaller hole and not the diameter of the 'nail head')

 

And thanks for the advices again. You have already helped more than the other forums altogether! :)

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Thanks for the tip, but the shipping would cost 8 euros and the gearboxes are too expensive on this webpage. It would even be cheaper (or the same price) to buy every single part separately. I checked for gearboxes in my country but I couldn't really find this type.

 

I'll check the trigger contacts. Although I don't know what it should look like. I hope I'll figure it out.

By the way I have 7mm bushings. (if it's the diameter of the smaller hole and not the diameter of the 'nail head')

 

And thanks for the advices again. You have already helped more than the other forums altogether! :)

Glad you find it helpful!

AK gearboxes are Version 3 and the one Lozart listed is compatible, bear in mind it includes the motor too, compared to UK prices its a good price for a complete gearbox with motor.

 

Anyhow the trigger contact switch has roughly parallel brass/ phosphor bronze contacts which are bridged by a metal contact which slots between them when the trigger is pulled. They should be clean and make good contact, any blackening is a sign of arcing (spark erosion) which reduces electrical efficiency (this alone can result in the motor not pulling the spring as you describe). So these parts should be clean (use a burnishing brush or fine wet & dry paper if need be) and the 2 parallel contacts should "spring" slightly when they are bridged (sometimes bending them toward each other a tiny bit helps but be careful they don't snap off, and also that the bridge piece still slides between them).

 

As for bushings yes its the diameter of the narrower part that counts (ie the hole in the gearbox shell they sit in).

 

Try Pete from this forum for parts, he may be able to sort you out. His website is:

 

www.ak2m4.co.uk

 

:)

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Glad you find it helpful!

AK gearboxes are Version 3 and the one Lozart listed is compatible, bear in mind it includes the motor too, compared to UK prices its a good price for a complete gearbox with motor.

 

Anyhow the trigger contact switch has roughly parallel brass/ phosphor bronze contacts which are bridged by a metal contact which slots between them when the trigger is pulled. They should be clean and make good contact, any blackening is a sign of arcing (spark erosion) which reduces electrical efficiency (this alone can result in the motor not pulling the spring as you describe). So these parts should be clean (use a burnishing brush or fine wet & dry paper if need be) and the 2 parallel contacts should "spring" slightly when they are bridged (sometimes bending them toward each other a tiny bit helps but be careful they don't snap off, and also that the bridge piece still slides between them).

 

As for bushings yes its the diameter of the narrower part that counts (ie the hole in the gearbox shell they sit in).

 

Try Pete from this forum for parts, he may be able to sort you out. His website is:

 

www.ak2m4.co.uk

 

:)

 

I cleaned every part of the switch but the piston still stops halfway. Nothing changed. :(

How is it that a few times it could actually shoot about 3 rounds if I released the anti reversal latch? I mean the motor should be good enough if it could do the work sometimes.

Anyway I hope this is all about those cheap plastic parts... I'll order a new piston and bushes.

Any kind of piston should fit in this gearbox that has 14 teeth or are there any other specifics?

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Update:

I managed to manually fire with the gearbox. I don't know if it's normal but I could barely do it through the bottom hole with a screwdriver.

Does this mean that the problem is not with the shimming/gears/bushing/piston but with the battery or the motor?

My battery is 8,4V 1600mAh.

And I still don't understand why sometimes the motor could manage to pull up the spring.

 

After I manually fired the gearbox and attached the motor, it could fire perfectly in full auto until I released the trigger. When I pulled the trigger again it failed and the piston got stuck halfway again.

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when you release the anti reversal latch the spring pushes the piston to the point of least resistance. Thus when you pull the trigger the motor has a few microseconds longer to build up torque and speed hence will fire, then if you stop firing, unless the spring is again under least resistance, the motor obviously isn't able to pull the spring for whatever reason. So if the wiring is ok and the battery is ok the motor does sound the likely problem.

By manual cycling I take it you mean turning the gears by inserting a screwdriver into the motor hole in the gearbox? Yes this is very hard to do on a fully working gun anyway so doesn't really prove anything.

One more thought, have you tried adjusting the motor height screw? This is usually a grub screw inside the cage that holds the motor in place, inside the hole the pistol grip screw screws into? Could be it needs slackening a little?

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when you release the anti reversal latch the spring pushes the piston to the point of least resistance. Thus when you pull the trigger the motor has a few microseconds longer to build up torque and speed hence will fire, then if you stop firing, unless the spring is again under least resistance, the motor obviously isn't able to pull the spring for whatever reason. So if the wiring is ok and the battery is ok the motor does sound the likely problem.

By manual cycling I take it you mean turning the gears by inserting a screwdriver into the motor hole in the gearbox? Yes this is very hard to do on a fully working gun anyway so doesn't really prove anything.

One more thought, have you tried adjusting the motor height screw? This is usually a grub screw inside the cage that holds the motor in place, inside the hole the pistol grip screw screws into? Could be it needs slackening a little?

 

Yeah you're probably right. This seems to be logical :P

After reading (probably) every single forum post about this, yes I have tried the motor at every possible level. It didn't change a thing. Not even the sound of it.

Well it seems like I'll have to spend more money on this.

Can I go ahead and buy a cheap motor? Or does the price matter?

 

Thank you for all the effort put into solving my problem! :)

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No worries pal! Its difficult to say 100% what is causing a fault accurately without seeing it first but from your descriptions it does sound as though the motor is likely to be the culprit. A cyma motor is probably your best budget choice as they are good for the price, or possibly a SHS which are a little dearer but again good for the money. Just make sure its the right type for an AK (V3 gearbox) when you order.

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It may even be worth just replacing the bushings first, it could be that tollerances are out slightly causing a tight spot in the gear meshing, before splashing out on a motor though.

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IMO stop spending money on parts you can only guess. Get it to an airsoft mechanic and he will fix it for sure and charge you only the needed parts apart from the service fee.

 

Bring it to WD or airsoftplaza or the mechanic in your area.

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IMO stop spending money on parts you can only guess. Get it to an airsoft mechanic and he will fix it for sure and charge you only the needed parts apart from the service fee.

 

Bring it to WD or airsoftplaza or the mechanic in your area.

 

Now that I spent long hours trying to solve the problem, I realised I'll need to buy new piston and bushes anyway, because they are made of plastic and are damaged.

If inserting these parts (which is needed anyway) won't help, I'm pretty sure it's the fault of the motor, because the wires and other parts seem to be fine.

And also it's my personal perversion to repair this myself :)

 

But your advice is of course the most logical step and you're right.

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