Solutions for piston moving too far back.

[ARC Fives]

The piston in this old G&G gearbox (I don't think the piston or rest of the internals are) locks back after a few shots.

I think the solution is to shortstroke by a couple of teeth (1 from front and one from back?) to stop the piston from moving all the way back and catching on the spring and spring guide. There isn't alot of space.

Or is this amout of space completely normal and I just need to try a different spring?

I don't have the tools to shortstroke the gear myself, so any low cost solutions would help.

View attachment 127218

 

[Leo Greer]

Absolutely not. What you need to do first is get a good LiPo battery. This lockup is occurring because your battery/motor don't have enough juice to complete the cycle, and thus the gearbox locks.

What battery are you currently using?

 

[Colin Allen]

The piston in this old G&G gearbox (I don't think the piston or rest of the internals are) locks back after a few shots.

I think the solution is to shortstroke by a couple of teeth (1 from front and one from back?) to stop the piston from moving all the way back and catching on the spring and spring guide. There isn't alot of space.

Or is this amout of space completely normal and I just need to try a different spring?

I don't have the tools to shortstroke the gear myself, so any low cost solutions would help.

View attachment 127218

it is very unlikely that the piston is catching on the spring and spring guide, although this is airsoft so anything is probably possible.

The usual cause of this is that the battery or motor lacks the muscles to push the piston all the way back against the heavily compressed spring.  

What battery, motor and spring are you using?

 

[Shamal]

Absolutely not. What you need to do first is get a good LiPo battery. This lockup is occurring because your battery/motor don't have enough juice to complete the cycle, and thus the gearbox locks.

What battery are you currently using?

Not doubting your diagnosis but how have you determined that the battery/motor don't have enough oomph?

 

[Pseudotectonic]

Can it slide freely with just the piston in the gearbox and when you shake it? I suspect the piston side rails are too wide (horizontally or vertically) for the gearbox so it is catching

Solution is sand down either the piston or the gearbox so when you shake it, it rattles freely

 

[Colin Allen]

Can it slide freely with just the piston in the gearbox and when you shake it? I suspect the piston side rails are too wide (horizontally or vertically) for the gearbox so it is catching

Solution is sand down either the piston or the gearbox so when you shake it, it rattles freely

That is also possible but, if it is going nearly all the way back, it is more likely that the motor and/or the battery is not powerful enough.

Not doubting your diagnosis but how have you determined that the battery/motor don't have enough oomph?

I realise that your question was not aimed at me; however, my answer would be that I have seen exactly that happen.

 

[Leo Greer]

Not doubting your diagnosis but how have you determined that the battery/motor don't have enough oomph?

That is also possible but, if it is going nearly all the way back, it is more likely that the motor and/or the battery is not powerful enough.

I realise that your question was not aimed at me; however, my answer would be that I have seen exactly that happen.

Very simply, this is an extremely common issue. Airsoft is rife with underpowered batteries being marketed as proper, weak ferrite motors in stock guns, and people who don't know what they're doing working on gearboxes that are badly designed and relatively complicated. Actually, I should say, the original design is genius but has been cloned, iterated, and become so outdated that it appears badly designed.

In addition, there's no other plausible alternative (to my understanding).

Here's what we know:

Gearbox locks after a few shots, doesn't unlock. The fact that this happens after a few shots means the piston isn't "too long" 

(or it could never cycle in the first place)

There's an aftermarket aluminum piston, which is a 17 tooth piston (I'm assuming this is an SR-25 or other 17T gearbox, though the OP's pics don't show the whole thing). If the piston were sticking, we should see obvious scraping from the successful cycles, which we do not...

Additionally, if the piston really were binding, the gears would simply free spin instead of causing a gearbox lockup. This is the easiest way to tell the difference: pull the trigger.

In conclusion:

Is it somehow possible that the piston, spring, gearbox rails, or spring guide are binding and causing issues? Yes... but how likely is that with no indicators?

Standard gearbox lockup is by far the simplest, most common, and most reasonable explanation. I see it constantly with people who don't know how to work on their guns, and who don't understand even vaguely how the batteries they use work. (Heck, I was one of those people once upon a time)

 

[Lozart]

Very simply, this is an extremely common issue. Airsoft is rife with people who don't know what they're doing

Edited for brevity.

 

[Asomodai]

I had this problem in a V6 gearbox which turned out to be using both a double bearing Piston Head and a double bearing Spring Guide. (Nothing to do with the battery) I had to get rid of the bearings on the spring guide to stop the piston locking towards the rear. If there is not enough space for the gears to complete the cycle and release the piston, It will lock. 

 

[ARC Fives]

Apologies folks, I never got notified that people have replied.

I have tried new batteries (including an 11.1), a new high torque motor that works perfectly in my other build, and new springs, ( a lower power and higher power springs to see if it makes a difference) and same problem.

I will try a different spring guide from another build and report back!

Thanks again everyone.