shredding pistons on my M4, need help

[BKHKMP5]

Hey guys. I'm really new to airsoft and I've never started with a stock gun. The first gun I bought was an MP5 peiced together from scratch by me. I never really got that working as I started with the Guarder SP120 upgrade kit. I purchased an M4 in peices all peiced together with CA and Systema parts. Anyways, I'm having problems shredding my Guarder polycarbonate pistons. I'm on my 3rd piston now. I've killed off 2 pistons in just an hour or so of testing. First piston was killed in my MP5 with the guarder SP120 spring. That probably wasn't a good idea. So now I'm using this setup on my M4.

Here's my gearbox parts...

King Arms V2 box
Guarder Cylinder
Guarder Piston head
Guarder Piston w/ steel teeth
Guarder gears
Guarder tappet plate
Guarder nozzle
Guarder spring guide
Systema shims
Systema springs
Systema selector plate
Systema switch/wiring
Systema bearings
Systema anti-reversal latch
Classic Army motor
PDI 120 spring

BTW, is the selector latch (metal peice inside gearbox) the same on MP5 and M4? For some reason in semi-auto and full auto modes it fires on full auto no matter what. Any ideas? The selector plate spring is there and I can see it on the outside pushing the latch back and forth.

I'm using a 9.6V battery, would going back to 8.4 help? I've read that the PDI 120 spring is just a step up from stock, so I shouldn't be killing off my guarder pistons. I get a really good ROF with the 9.6, so I assume that's what's killing off the pistons. However, just wondering if anyone thinks it could be something else. Should I change to an aluminum piston?

I do intend to go to games in the future, but I need to get at least one of my bloody guns working first. I plan to rebuild the MP5 stock and use it for CQB. M4 may never be reliable enough for games.

Thanks in advance,

Bryan

[Foofighter]

From not knowing anything about AEG's I would guess that running a battery thats overpowered is whats killing your pistons...

[ThunderCactus]

If your using a large battery, use an 8.4v, and try a systema or G&P piston.

[Sha Do]

In order to really help you out on this I'd have to see the AEG and actually tear it down. The full auto thing could be one of a couple of things....it could be your selector plate is damaged, the copper contacts at the selector plate are bent out (so there is continous contact), and so on.
The pistons could be getting chewed up because the slider slots on each side of the mech box are to tight (or narrow), so when you assemble the box the piston is not traveling freely.
There are just too many possabilities.....Best to have the mech box looked at by a tech (say GUMP, SCHWAG, or the likes).

SHA DO

[BKHKMP5]

Thanks guys.

The selector plate and switch assembly is brand new. I bought it new and installed it the same day I was testing it. As for the rails for the piston, I used the piston in a CA, TM and KA box and it still did the same thing. When I physically move the piston on the rail it seems to move with ease. Shouldn't they all be standard anyways?

If I plan on replacing the piston, will it be compatable with my Guarder gears? If not, which brand should I buy?

I had DarkAngel assemle my gearbox, so everything was greased properly, etc.

Thanks!

Bryan

[six4]

Originally Posted by BKHKMP5

Hey guys. I'm really new to airsoft and I've never started with a stock gun. The first gun I bought was an MP5 peiced together from scratch by me. I never really got that working as I started with the Guarder SP120 upgrade kit. I purchased an M4 in peices all peiced together with CA and Systema parts. Anyways, I'm having problems shredding my Guarder polycarbonate pistons. I'm on my 3rd piston now. I've killed off 2 pistons in just an hour or so of testing. First piston was killed in my MP5 with the guarder SP120 spring. That probably wasn't a good idea. So now I'm using this setup on my M4.

Here's my gearbox parts...

King Arms V2 box
Guarder Cylinder
Guarder Piston head
Guarder Piston w/ steel teeth
Guarder gears
Guarder tappet plate
Guarder nozzle
Guarder spring guide
Systema shims
Systema springs
Systema selector plate
Systema switch/wiring
Systema bearings
Systema anti-reversal latch
Classic Army motor
PDI 120 spring

BTW, is the selector latch (metal peice inside gearbox) the same on MP5 and M4? For some reason in semi-auto and full auto modes it fires on full auto no matter what. Any ideas? The selector plate spring is there and I can see it on the outside pushing the latch back and forth.

I'm using a 9.6V battery, would going back to 8.4 help? I've read that the PDI 120 spring is just a step up from stock, so I shouldn't be killing off my guarder pistons. I get a really good ROF with the 9.6, so I assume that's what's killing off the pistons. However, just wondering if anyone thinks it could be something else. Should I change to an aluminum piston?

I do intend to go to games in the future, but I need to get at least one of my bloody guns working first. I plan to rebuild the MP5 stock and use it for CQB. M4 may never be reliable enough for games.

Thanks in advance,

Bryan

im taking a total shot in the dark here,( not a gun tech ) but here's a couple scenerios:

1) perhaps the piston is not the right length. at a guess im wondering if the piston isnt allowed to complete its stroke due to compatibility issues and being chewed up by the gears.

2) are you testing your install with your hop up on? ive only ever seen it on mp5's but to much hop up after a new install can jam the weapon,something has to give and its usually the piston getting shredded.

hope that helps.

[BKHKMP5]

Originally Posted by six4

im taking a total shot in the dark here,( not a gun tech ) but here's a couple scenerios:

1) perhaps the piston is not the right length. at a guess im wondering if the piston isnt allowed to complete its stroke due to compatibility issues and being chewed up by the gears.

2) are you testing your install with your hop up on? ive only ever seen it on mp5's but to much hop up after a new install can jam the weapon,something has to give and its usually the piston getting shredded.

hope that helps.

The piston came with the Guarder SP120 kit I bought. I just replaced the spring with the PDI one. Guarder only makes one piston so it should match up with the gear set.

I'm testing with no hopup. The gearbox is out of the gun, just the grip and motor installed.

I'm just wondering whether I should bother getting other guarder piston then going to the 8.4V battery or if I should be looking at something else.

thanks,

bry

[six4]

Originally Posted by BKHKMP5

The piston came with the Guarder SP120 kit I bought. I just replaced the spring with the PDI one. Guarder only makes one piston so it should match up with the gear set.

I'm testing with no hopup. The gearbox is out of the gun, just the grip and motor installed.

I'm just wondering whether I should bother getting other guarder piston then going to the 8.4V battery or if I should be looking at something else.

thanks,

bry

just so we are all clear on how you are testing,are you testing the set up out of the gun with only the grip and motor attached and not actually testing it fully assembled?

[BKHKMP5]

Originally Posted by six4

just so we are all clear on how you are testing,are you testing the set up out of the gun with only the grip and motor attached and not actually testing it fully assembled?

Correct. However, I'm only doing this after I tested the gun fully assembled. When it was fully assembled I only got full auto in the semi-auto and auto position. Safety works fine. I didn't want to dry fire the gun and worry about hopup problems so I took the gearbox out to test it.

[ThunderCactus]

All gears will work with all pistons, with the exception of unlimited or infinity torque gears that require half tooth pistons.
Actually I just remembered, theres a guarder piston in my M4 and it wouldn't work when I tested it. As it turned out, having an aluminum piston head, the piston was too far forward for the first tooth on the piston to get grabbed by the gear, instead it would just jam up so I had to make a spacer for it.
If the same is happening on your gun, your gears may have worn down that first tooth on the piston and weakened it causing it to break.
So either try a silent head set (piston and cylinder heads), as the silent head is a bit thicker than the poly or aluminum heads, or put a shim between the piston head and piston.

[BKHKMP5]

Originally Posted by ThunderCactus

All gears will work with all pistons, with the exception of unlimited or infinity torque gears that require half tooth pistons.
Actually I just remembered, theres a guarder piston in my M4 and it wouldn't work when I tested it. As it turned out, having an aluminum piston head, the piston was too far forward for the first tooth on the piston to get grabbed by the gear, instead it would just jam up so I had to make a spacer for it.
If the same is happening on your gun, your gears may have worn down that first tooth on the piston and weakened it causing it to break.
So either try a silent head set (piston and cylinder heads), as the silent head is a bit thicker than the poly or aluminum heads, or put a shim between the piston head and piston.

The gearbox wasn't jamming though. It would cycle through properly. Basically it would just keeep firing, then ocasionally slip (which is the point when I think the piston gears were wearing down), and eventually just wouldn't cycle at all (which is when the gears were completely shaved off).

Do guarder pistons suck? Do I need to match up pistons w/ piston heads or can I use my ball bearing guarder piston head with other brands of pistons?

Thanks,

Bry

[six4]

Originally Posted by BKHKMP5

The gearbox wasn't jamming though. It would cycle through properly. Basically it would just keeep firing, then ocasionally slip (which is the point when I think the piston gears were wearing down), and eventually just wouldn't cycle at all (which is when the gears were completely shaved off).

Do guarder pistons suck? Do I need to match up pistons w/ piston heads or can I use my ball bearing guarder piston head with other brands of pistons?

Thanks,

Bry

if your consistently firing it out of the weapon,,( testing with just the grip and motor attached as you stated you are doing ),,its still dry fire and that will kill your mechbox faster than anything. avoid dry firing whenever possible, one or two cycles is acceptable for testing but nothing more.

[ThunderCactus]

Originally Posted by BKHKMP5

The gearbox wasn't jamming though. It would cycle through properly. Basically it would just keeep firing, then ocasionally slip (which is the point when I think the piston gears were wearing down), and eventually just wouldn't cycle at all (which is when the gears were completely shaved off).

Do guarder pistons suck? Do I need to match up pistons w/ piston heads or can I use my ball bearing guarder piston head with other brands of pistons?

Thanks,

Bry

yes you can, try a systema red piston.

[BKHKMP5]

Will do, I'll give the systema piston a try with a lower voltage battery and report back.

Getting a piston with titanium gears would probably destroy my gears right?

Thanks!

Bry

[ThunderCactus]

Good metals kill pot metals