Big problems v2 gearbox, need help!

[Grevn]

I installed a swiss arms cylinder, cylinder head and piston head and also an element piston. After about 1000-2000bbs the piston locked up to the back of the gearbox, and it ler me fire a few shots then locked up again over and over.

I opened the gearbox and found metaldust everywhere. The pistonhead had come lose and was barely attached to the piston and had scraped the inside of the cylinder. The Pistons teeths were also chewed up pretty bad, Worst at the piston tooth but also alot at the teeths closest to the piston head.

Im getting a new cylinder and piston but i really need help to figure what could have caused all this. Worth to note is that i completly forgot to fix aoe and loctiting the pistonhead screw, but could that have destroyed those piston teeths so bad?
Help plz!
Sorry for my half decent English and greetings from sweden 😊

[RainyEyes]

Here watch these:

https://www.youtube.com/watch?v=sI7agUdUsz4

https://www.youtube.com/watch?v=-8LKhM79McM

Loctite the piston head? No. That won't cause it to break.

Fixing aoe? maybe.

You're more likely to have badly shimmed gears or something.

[Grevn]

ok so if the shimming was the problem, would it be that it was too loose then? i dont know that much but sounds wierd that the teeths closest to the piston head would strip due to that?

[RainyEyes]

Originally Posted by Grevn

ok so if the shimming was the problem, would it be that it was too loose then? i dont know that much but sounds wierd that the teeths closest to the piston head would strip due to that?

Too loose/too tight can cause performance issues but it won't cause the piston to break. Sometimes you just get bad luck or the piston is bad quality. The shimming and AOE is just for better performance but if the gears break because of bad shimming the pieces can jam other parts and screw everything up.

What is the current set up? What is the strength of the spring, relative to the bb's feet per second, that you're using, with the piston that you've installed?

[Grevn]

its a specna arms b10, in the gearbox i have a new swiss arms cylinder, swiss arms cylinder head, swiss arms piston head, element full metal rack piston and the rest is stock. The gears seems fine, just the piston and cylinder that got destroyed.

i chronoed it to 100m/s with .28g bbs with a m120 spring.

what i think maybe have happend is that when the piston head came lose it increased the friction in the cylinder that maybe caused the sector gear to chew upp the piston and push around the piston, scraping the cylinder, maybe? :P

[Grevn]

i totally reshimmed everything now, everything is set so when the gearbox is tighten the gears have a very small amount of play, but if i would put in 1 more .1mm shim on the gears they would be to tight. That is the way to do it right? they also have great contact to each other without scraping.

[RainyEyes]

Originally Posted by Grevn

its a specna arms b10, in the gearbox i have a new swiss arms cylinder, swiss arms cylinder head, swiss arms piston head, element full metal rack piston and the rest is stock. The gears seems fine, just the piston and cylinder that got destroyed.

i chronoed it to 100m/s with .28g bbs with a m120 spring.

what i think maybe have happend is that when the piston head came lose it increased the friction in the cylinder that maybe caused the sector gear to chew upp the piston and push around the piston, scraping the cylinder, maybe? :P

M120 spring on stock gears will cause full gear cycling which indicates to me that your piston may not be designed for that amount of stress. The angle of engagement is more critical since you have a full metal teeth rack on the piston. Metal on metal will typically cause a catastrophic failure compared to plastic on metal contact.

By the way the standard chrono is .20g bb's for most North American fps limit measurements. 100m/s is about 350fps, but with an m120 spring expect about 400 fps on .20g bb's. Try to re-do the chrono on .20g bb's if possible.

Usually loctiting the piston head isn't an issue, but it doesn't hurt to do it anyway.

You should try to use the bevel-pinion method to shim for the best performance.

If you could, please post some pictures so that we can see exactly where the failure occurred and we could possibly give some input on how to prevent it.

[Grevn]

Originally Posted by RainyEyes

M120 spring on stock gears will cause full gear cycling which indicates to me that your piston may not be designed for that amount of stress. The angle of engagement is more critical since you have a full metal teeth rack on the piston. Metal on metal will typically cause a catastrophic failure compared to plastic on metal contact.

By the way the standard chrono is .20g bb's for most North American fps limit measurements. 100m/s is about 350fps, but with an m120 spring expect about 400 fps on .20g bb's. Try to re-do the chrono on .20g bb's if possible.

Usually loctiting the piston head isn't an issue, but it doesn't hurt to do it anyway.

You should try to use the bevel-pinion method to shim for the best performance.

If you could, please post some pictures so that we can see exactly where the failure occurred and we could possibly give some input on how to prevent it.

hehe yeah i know, I had only chronoed it with my .28 at a game, 2 hours before it all broke down. but i have ordered a chrono that will arrive any day now.

yeah, will shim it to the motor. one more thing btw, one screw hole for the handle to the geabox was stripped when i got the gun, can this cause alot of problems?

will put up picks in a couple of minutes

[ThunderCactus]

Element pistons are not good, try using SHS instead.
If the piston head came loose, it's because you didn't use threadlock on the screw. It always vibrates loose unless it's threadlocked in place.
Gear wear could very well be from the piston head being loose; in the forward position the piston might be sitting on the piston head boss, changing your angle of engagement.

It's possible the piston body is out of spec for your mechbox as well, it could be tightening up at the back. So with the next piston, throw it in the mechbox without a cylinder, spring, or spring guide, and see how easily it moves back and forth in the shell.

But if the mechbox was locking up with the piston all the way back, and the motor wouldn't move it, it's possible your motor might just not be strong enough to move the piston with that much tension on it.

[Grevn]

Originally Posted by ThunderCactus

Element pistons are not good, try using SHS instead.
If the piston head came loose, it's because you didn't use threadlock on the screw. It always vibrates loose unless it's threadlocked in place.
Gear wear could very well be from the piston head being loose; in the forward position the piston might be sitting on the piston head boss, changing your angle of engagement.

It's possible the piston body is out of spec for your mechbox as well, it could be tightening up at the back. So with the next piston, throw it in the mechbox without a cylinder, spring, or spring guide, and see how easily it moves back and forth in the shell.

But if the mechbox was locking up with the piston all the way back, and the motor wouldn't move it, it's possible your motor might just not be strong enough to move the piston with that much tension on it.

cant get ahold of an shs here in sweden, what about a madbull px02?

yeah, i just completly forgot the threadlock :/

the piston moved great without a spring in, so my guess it that it was the pistonhead that jammed it, or the chewed up piston. it worked for the first 1.5k bbs i shot through it.

pictures coming up now!

[Grevn]

dem pics

piston teeths:

another angle:

and another angle:

about how the piston head looked when i opened it up :

scraped cylinder:

more scraped cylinder (from other side):

You guys think that the cylinder is usable or will i lose a ton of compression?

this wear is of only about 2000bbs, so thats pretty nuts :s

[ThunderCactus]

Cyclinders scrap.
Looks like the piston head was catching in the cylinder, which explains some of the wear on the piston rack, but that rack also looks like its really soft metal.
Cant import SHS?
Use a plastic piston head, less danger to the cylinder if something like this happens.

[Grevn]

Originally Posted by ThunderCactus

Cyclinders scrap.
Looks like the piston head was catching in the cylinder, which explains some of the wear on the piston rack, but that rack also looks like its really soft metal.
Cant import SHS?
Use a plastic piston head, less danger to the cylinder if something like this happens.

oh damn, that what was i thought oh well.

just looked it up, a local shop actually got them, wich one do you think is the best? this is the shop that got them, maybe google translate will do a decent job so u can understand what it says .P http://www.rodastjarnan.com/sokmotor...ms=shs+pistong

is this one good?

any suggestions for good piston heads?
is there any downsides to a plastic piston head?

i was thinking that i would try fix all the problems with the ruined cylinder and make sure it doesnt keep scratching, and when im sure it doesnt scratch i put in the new cylinder and use the old piston head. is that a good way to go at this problem?

[ThunderCactus]

http://www.rodastjarnan.com/airsoft/...altander-35038
This is what I'm using in my 38rps M14, really liking it.
No downside to plastic head
install all the new parts at the same time.
Test your shimming, too. Make sure none of the gears rub against eachother, and the tappet plate still moves freely when the mechbox is shut.

[Grevn]

Originally Posted by ThunderCactus

http://www.rodastjarnan.com/airsoft/...altander-35038
This is what I'm using in my 38rps M14, really liking it.
No downside to plastic head
install all the new parts at the same time

ok nice, thanks alot, gonna go ahead and buy it tomorrow then!

do you know of any good plastic piston heads? or should i just test properly with the stock plastic one and the put in my alu when i know its safe?