Big problems v2 gearbox, need help!
 

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 😊

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.

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?

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

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.

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

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! :)

dem pics

piston teeths: http://i.imgur.com/XnpzbJD.jpg

another angle: http://i.imgur.com/MeJokuT.jpg

and another angle: http://i.imgur.com/7tJ2AIn.jpg

about how the piston head looked when i opened it up :http://i.imgur.com/rVFx8z3.jpg

scraped cylinder: http://i.imgur.com/yjuV0R5.jpg

more scraped cylinder (from other side): http://i.imgur.com/jUbIw0p.jpg

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

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? http://img.rodastjarnan.com/airsoft-...r-35034-f1.jpg

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?

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.

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

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?

Lonex POM piston head

element pistons use metal that is softer than plastic. lol. That rack might have well been made of cheese.

ok i went on a shopping spree today and bought everrything i needed to fix it and a little bit more haha :D

so i went shs full steel rack /w 14teeths and rest dream army. Ive heard that those give really good compression if used togehter. I also did a total reshim and shimed it to the motor pinion, i gave the bevel gear about 1/2mm play when the motor is in and used threadlock on the motor adjustment screw. I also threadlocked the piston head.

havent adjusted aoe yet, have to find some decent rubber or somthing to do it with.

them upgradeparts:http://i.imgur.com/1YREBaQ.jpg

this is the aoe right now, does it need fixing? http://i.imgur.com/KeSaZ8p.jpg

and then i decided to instal a mosfet because I wanted to :) http://i.imgur.com/g3D540K.jpg

i will test all this tomorrow (clock is about 22:30 here in sweden and i work tomorrow) but before i do that, should i put silicon oil on all the o-rings? should i grease up the gears a little bit?

and btw THANKS ALOT for allt he help you guys already have given me, it really helped a noob alot! and especially thanks for the tip about the shs piston, that thing feels solid as a beast compared to the shitey element that broke, and they were the same price >.>

I have a feeling that OP was right all along and the piston head loosened itself and started to smack the cylinder when it was being drawn back in the gear cycle. If what lurkingknight says is true and evidence suggests it is, then the Element parts started to break under friction and the threads started to break after so many shots.

Also, if you're looking for some good rubber, some plumber o-rings will do just fine. Try looking for sorbo pads online if you're really adamant on paying for the extra quality, but anything from local home hardware stores usually have what you need.

Yeah thanks for the reminder! Will do that before putting together! :)
I got teflon Grease for the gears and silicon oil, am i supposed to put a little bit on the o-rings?

Ok thanks alot, will check if i van get ahold of some sorbopads here in sweden If not, then orings it is. If i go with orings, do i just put one on there, or do i put several with different diameters?

About the aoe this is what it looks like without modinghttp://i.imgur.com/E5iJICah.jpg

Would this be a proper aoe? http://i.imgur.com/VATSUVSh.jpg

Just one: https://youtu.be/sI7agUdUsz4?t=9m3s

Follow that guide, that usually won't lead you wrong. Unfortunately over time the o-ring will compress over time so try to account for 1-2mm of over-correction.


That looks MUCH better, but a few degrees more would be optimal. You're at about 80 degrees, try to aim for 90-95 degrees. You need to put the spring in to account for compression.

Ok sweet, thanks alot, will buy o-rings and fix tomorrow! 😁

Ok sweet thanks!

What i have home is silicon oil and teflon grease, what is the best out of that for o-rings? I have no Idea If teflon Grease is synthetic or not hehe.

Typically silicone oil is best for the o-rings but not great for metal on metal-contact. Depending on the viscocity it will just get spread all around the gearbox... except the parts you want covered...

Oh ok, just found out what silicone Grease is to, got a completly different name in swedish "armaturfett" instead of silikonfett that Woolf be the logical translation, Will probably pick up a Tube of that too tomorrow.

Then i Will put teflon grease on the gears and silicon Grease on the o-rings and a little bearing oil in the bearings ��

Your unmodded AOE is fine, its not actually that critical to get it 100% perfect as the gear tooth profile is convolute, not flat.

ok so i have fixed everything and put it together and my chronogragh arrived today :D

it shoots 128-132 m/s with .20
and 108.5-110 ,/s with .28
i have a m130 spring installed, would this suggest that i have good compression in the gun?

And thanks alot guys for the help and guidance! :D

a wierd thing though is that it doesnt want to ffed from my highcap anymore (that came with the gun), but it feeds prefectly with my ca midcaps(wich is the only ones i use anyway) ^^

Here is how you check compression: https://www.youtube.com/watch?v=MFnUjxdiXuU

I would not advise you disassemble to check again because those numbers look normal to me. Just something for later when you open it again for maintenance or something.

Does the mag wiggle in the mag well when inserted, if you added a new hop up unit too sometime the catch for bbs may not be pushed out the way to release them

Sent from my LG-D852 using Tapatalk

A come on haha, how do you manage that? Very tight barrel or just insane compression?

I will pull it apart After the weekend to check how everything is Holding up After playing saturday and sunday.

Btw, were i supposed to put silicon Grease on the cylinderhead o-rings? And teflon Grease on the Pistons teeth?

Ive been finding more people with high fps on low springs lately. Cant help but wonder if its the springs and not the guns....
I recently tested a pair of SHS springs in a pair of guns, and found they both shot 30fps over their target, but according to reliable sources they lose 30fps once they settle.
Ive known some springs in the past to shoot over their ratings, and mislabeled springs is nothing new to airsoft. Buying a guarder spring used to be a game of roulette. In fact we used to buy a pair of springs when upgrading just to make sure we got ONE properly packaged spring lol

aah come on, physics is my enemy, im a carpenter haha ;D But shouldnt the fps of the bb only come down to barrel length, barrel inner diameter, cylinder volume, spring and compression? or am i missing something? :P

i have the right cylinder volume if what the dream army chart of their cylinders is true, 6.03 363mm barrel, 130m spring. maybe my compression is off, gonna test to mod the bucking to not loose anything there :)

im shooting .3 bbs now btw

hehe thats true, ive got a madbull m130, and since i shoot 130m/s with .2s thats pretty spot on :)

Here is the beauty btw ^^
http://i.imgur.com/Hp0qB8y.jpg http://i.imgur.com/twdC46e.jpg:D