[aotsukisho]

I've searched around and there is a surprisingly few number of photos of mechanical gearbox shell failure aka "v2 cracking". There are way more photos showing up on how to properly radius or do other modifications to mitigate it. In order to better understand differences between each companies' particular casting alloy and the effect of different styles of gearbox design (usually combined attributes) I am interested in seeing if there is a trend particular to companies' designs in terms of specifically how they fail.

I understand that this is going to be majority v2 type gearboxes, which is fine. I personally am mostly interested in v2 and v3 anyway. However, photos of any version gearbox with any type of catastrophic mechanical failure is welcome to demonstrate failure methods.

If possible, please include the brand of gearbox if that information is available. I'll kick off the thread with some that I found around the web. There is quite a few photos but few of same brand, I am interested in getting as many data points as possible.

A&K v2

G&G v2

G&G v2

JG v2

King Arms v2

KWA v2 (original)

Modify v2

Systema v2

Unknown brand v2 (VFC?)

Unknown brand v2 (Tokyo Marui)

 

[Guges Mk3]

You KWA one is gen 1. 2GX does not break very easily.

The one of the Colt is a TM

 

[OPairoft]

The first unknown is a vfc I believe.

 

[OPairoft]

Second unknown looks like a tm since it has the two piece hop up and the color of the shell.

 

[Gray.]

The front of the gearbox cracked, but only on half of the shell. (At least for now)

 

[kazuchan]

G&G v2 look fun, they "tried" to fix it haha!

 

[BeansOnToast]

I feel like this one is directly aimed at me, I'll get a photo posted.

 

[danerd]

Modify 9mm shell. Radiusing done my myself. Also had 3/8" 50D Sorbo pad. Cracked under an 8T SP170 DSG ~ 2000 rounds.

 

[Ben3721]

Even with the radius and sorbo... that's the first I've seen that. That sucks. The metal probably had something wrong with it.

 

[danerd]

Even with the radius and sorbo... that's the first I've seen that. That sucks. The metal probably had something wrong with it.

Could very well have been. It was a spare shell I had laying around for the better part of ~10 years or so. Never really got around to building it out; go figure that this happens when I decide to do so.

 

[modularvideo]

I wonder what the failure-rate is for the most common brands' gearboxes, for periods of say, 20K, 50K, and 100K rounds. Or other metric analyses; e.g., operation-time vs. percentage-of-duty time, etc.

 

[aotsukisho]

I wonder what the failure-rate is for the most common brands' gearboxes, for periods of say, 20K, 50K, and 100K rounds. Or other metric analyses; e.g., operation-time vs. percentage-of-duty time, etc.

That's kind of what I was going for when starting the thread, there are lots of reports of G&G v2 being fragile and the fact that two G&G photos showed up doing an image search (along with their modern G2 being specifically strengthened in the front) lends me to believe it. I also don't doubt the claims of Evike G&P gearboxes being fragile but there are no photos yet. Usage metrics are impossible to state accurately but perhaps some information can be had by the quantity of reports per brand, and perhaps the angle/severity of crack.

Thank you for your contribution @danerd looks like a different version Modify v2 than the one I originally found.

 

[Guges Mk3]

Hmmm...I wonder if I can find that FB video where a G&P Boy was asking me WTH...as he was smashing the Evike G&P shell with the plastic end of a screw driver back in 2013...

 

[Ben3721]

The issue is any crack at all on the thinnest segment of the radius will work its way through.

A lot of casted shells that have the radius casted in have some thin casting edges that basically still spots that still will crack.

A shell needs to be radiused before having a round count over 5k and it needs to be even without any thin spots in the curve.

Even then I remember shells cracking in the back of the window down past the bushings in bad pot metal mixes.

 

[modularvideo]

. . . A shell needs to be radiused before having a round count over 5k and it needs to be even without any thin spots in the curve.

Hmmm . . . well I'm probably nearing 5K rounds on several guns (hi-caps, ya know!). Guges says if I'm just backyard-plinking not to worry about mechbox-upgrades, but your post gives me some pause. My Cybergun VFC SCAR (with a non-Avalon gearbox) and pending ICS MP5 will be getting a lot of BBs put through them.

 

[Hyperslow556]

Believe it or not, this works...

You will always get cracks forming in powder pour GB shells, regardless of what modifications are done to the powdered metal. This device wont stop cracking issues, but it will keep the front of the GB in place if there is a failure. I played through an entire 6 hour game with a GB shell that busted up front, but having the Shock block installed allowed the unit to perform the entire game until I got home.

I would suggest that high-cycle builds over SP140 use this.

 

[Graybeard]

You tech guys ever use JB weld on the mech box?

 

[Ben3721]

You can't really fix a cracked shell long term.

A shock transfer unit will help to prevent snagging crack, but they typically aren't very well made.

Another thing is spacing the hop up hard against the front of the shell. It's not as good but it does help. Much better than a spring holding the hop to the shell.

 

[Guges Mk3]

You tech guys ever use JB weld on the mech box?[/QUOTE

Introducing an epoxy on the surface does very little in replacing the strength of the alloy shell in a "joint". This is due to the fact the epoxy doesn't truly form a molecular "bond" with the cracked metal.

Like our "infrastructure":

No one is using epoxy to fix bridges....

It's just an adhesive and if the adhesive doesn't stick any more...it will fail again.

The Shock transfer system only works on a few models...one could in theory make a STS system out of metal rods.

 

[89927]

Im curious about any information on krytac v2 gearbox vs lct gearbox for the lct rpk lck16(which im not even sure which model gearbox is in it, various ones on brill with/without mosfet). Krytac lmg gearbox vs lct lck16 gearbox. I generally shoot 2-5k per round. Which overall wins out for durability?