Self detaching piston head..

[Adam3088]

So after rebuilding a v2 gearbox it fired 50odd shots fine, suddenly seizes up with the piston all the way back, spring tension release wouldn't move the AR latch so I had to open it up under full tension.

Cant see anything wrong with the gears/av latch but the piston head had detached itself from the piston..

It's a ZCI silent head on a ZCI piston, stock cylinder + head with neoprene pads glued on to fix the aoe.

View attachment 16305

Any reason why this might have happened? The head was very well attached when it all went together, and still cant understand how it seized..

 

[Monty]

Screw looks a bit bent.

 

[Adam3088]

Yeah, think that probably happened after it broke free

 

[Lozart]

Buy some thread lock. Probably just the screw come loose and undid itself.

 

[Sitting Duck]

This stuff happens quite a bit to piston bearing heads

as Lozart said used Loctite thread sealant/glue

or drop the bearing......

some boxes like G&G's D-Boys have seen 5mm plastic spacers in there instead

is lighter and tensions the spring a smidge a bit more like the bearings

but less likely to come undone - it is something to do with bearing race

5mm thick by 20mm diameter

or

10mm thick by 20mm diameter - but only for use on short stroked pistons

(as spring may hit its compression limit on full stroke setups)

http://www.ebay.co.uk/itm/10-Pack-M6-6-3-mm-Inside-D-Nylon-Plastic-Spacers-Various-Sizes-and-Lengths-/231063250182?pt=LH_DefaultDomain_3&var=&hash=item35cc716506

these have a M6 hole in them and need to be widened a little to accept the bolt/bearing sleeve

but that is what the CM16's have in them and found same setup in the dboys 416 even though it was said to have bearing piston head

I actually now go without bearings on piston to save weight and as long as a bearing spring guide is fitted the spring can still untwist

It happened to me also once even though I tightened it like f*ck

and happen also on a gun I bought s/hand

Threadlock MUST be used on piston bearing heads or imho it will happen - not if - it will happen at some point

blue is medium strength and should be ok

red is high strength and may be a lot harder to undo - heck might need cutting piston head off if piston strips at some point

pretty sure the bolt in there is M3 thread but unsure of exact length - could be about 12mm-ish

but best measure to be sure if you need to get a replacement one

M3's are used in most instances for gearbox case bolts, pistol grips on v2 boxes, motor frame/cages on v3's & piston heads bolts if not self tapping ones etc....

 

[Adam3088]

Ahh ok, didn't realise bearing heads were more susceptible to undoing themselves.

I've stuck a load of blue loctite in there so will so how it holds up this time, was a bit surprised it had undone itself after so few shots as I'd tightened it up pretty well.

I'll see how it goes this time, if it comes off again I'll remove the bearing, thanks!

After sitting down for a while I realised why it had seized up, when the head detached the piston must've been unable to travel all the way forwards (screw in the way or whatever), so when the gear picked it back up it pulled back to the release point but there were still teeth left to pull it back, resulting in jammage.

On a slightly related note, I've got a M100 spring to go in it (one of those springs where not all the coils are evenly spaced) but holy sh*t the amount of effort required to actually get it into the gearbox is unreal, are they normally that difficult when new? Thinking of clipping off a couple of coils so I can actually get it in.. Only other v2 I've taken apart was my M4 and that spring went back in very easily.

 

[Sitting Duck]

don't cut any coils - yet

besides coil cutting is a bit of a bodge or a last resort

the tighter coils - where they are closer spaced together goes at back/spring guide

designed this way as slightly lighter tension when starting to compress spring on semi

often you may find the coils tighten in middle and at back of spring

if they are close together at front you got it ar$e about face

if you install a spring incorrectly you will lose final tension/fps and it is said it makes more work from standstill/semi

think I noticed about a 20fps drop when I fitted an irregular spring back to front

it could be wrongly labelled m100 but shs springs are deffo a bit generous I found recently

plus wire used is thicker than stock spring wire

had a m125 (- didn't think they did 5 increments) and thought I would fully compress it for 12 hrs to lose tension a smidge

yeah - still seemed way stronger than a stock m120 spring I ended using for a short stroke project

to really know for sure is by chucking it in and seeing and then you would need a chrono - no real other way

if you have fitted a spring guide over a stock spring guide then that should push you back up to any loss from aoe

better seals and bearing on piston adds another 5mm compression on spring - same as bearing spring guide

So unless your gun was well n truly low you should be about 5 to 10% up on old figure

as long as nozzle is sealing good in the hop

You could try the m100+ spring but reckon only if you got chrono to hand if you suspect it is bloomin' strong mofo

couple of bursts will soon show if she is over or not

if over you could remove a tooth - shortstroke but tbh I doubt if your gun is gonna run a risk of PE unless 11.1v

way up the pro's n con's, see if you can remember what she was shooting at previously and maybe if she was low then try m100+

Short stroking isn't that tricky - each tooth will reduce final fps by about 6% or multiply fps by 0.94 & repeat

however not much room for SS on longer barrels like full AK's @ 455mm etc....

but room for a couple on 400 & below barrels

doubt if you need to get into this crap just yet - put her back as an improved slightly upgraded/stock box and see how she goes

 

[Adam3088]

The stock spring in WE aeg's is an odd one, it's quite a bit shorter then a standard spring but is also softer then the M100 I have. Stock one was shooting at ~260ish.

Wondering if the M100 spring is being a bit over-compressed as it's now got bearing guide + head + pads fixing aoe?

My air seal is very good now, put an o-ring nozzle in there combined with the new piston head, didn't even need to tape up the cylinder head.

Think I'll try to compress the M100 a bit overnight, don't want to shortstroke really as the piston only has 1 steel tooth.

 

[Shizbazki]

Hi mate i am guessing this is for your SCAR-L?

I did some tech work on my mates WE SCAR and found the out of box performance a bit pants (around 280 FPS).

Yes i would say the spring also feels weaker than a M100 spring, it was one of the first things i changed in his gun when i upgraded it.

As for the piston what i will add is that the WE AEG gearboxes are very sensitive when it comes to the length of the piston, I replaced the original piston with the Mad Bull Alien Green one and could not for the life of me figure out why the gearbox kept locking up on full auto. It wasn't till i measured (with a digital micrometer) the Mad Bull one with the original one that i noticed the Mad Bull one was about half a millimeter longer, when i installed another piston about the same length as the original it worked fine.

But yeah, clean the screw and screw hole, add loctite, put it back together, let glue dry and test fire a few shots.

 

[Sitting Duck]

ahh - then you can't SS - lol

now you explained the bespoke or shorter spring then ok I see then it would be stronger

Never quite understood these slightly special boxes with shorter springs like on 21's or arx160 etc...

If it has 16 teeth piston n sector........

anyway if she is say 15-20 over then if the stock spring guide wasn't bearing then that might get you back to 350 ???

could work maybe - if later on fpd drops in 6 months - pop bearing one back in there

only way to know for sure is try it all in there with m100 - but yeah m100 would deffo be a bit tougher compared to 260fps

(if it was down to spring mainly)

soz for waffle n all that but just saying a few ideas before you reach for hacksaw/dremmel

(you could fit spring ar$e about face to lose fps but as I said techy's don't advise it due to increased starting tension)

 

[Sitting Duck]

Hi mate i am guessing this is for your SCAR-L?

I did some tech work on my mates WE SCAR and found the out of box performance a bit pants (around 280 FPS).

Yes i would say the spring also feels weaker than a M100 spring, it was one of the first things i changed in his gun when i upgraded it.

As for the piston what i will add is that the WE AEG gearboxes are very sensitive when it comes to the length of the piston, I replaced the original piston with the Mad Bull Alien Green one and could not for the life of me figure out why the gearbox kept locking up on full auto. It wasn't till i measured (with a digital micrometer) the Mad Bull one with the original one that i noticed the Mad Bull one was about half a millimeter longer, when i installed another piston about the same length as the original it worked fine.

But yeah, clean the screw and screw hole, add loctite, put it back together, let glue dry and test fire a few shots.

Ahhhh - yet another one of them mofo things to check.....

maybe drop the spring guide if spring compression space is limited just to be on safe side and go with a non-bearing guide

(you got bearing welded onto piston now so maybe ease up on extra bearings compressing spring)

I'm signing off as I don't know jack - well deffo mega FA on WE Scar stuff

 

[Shizbazki]

Ahhhh - yet another one of them mofo things to check.....

Trust me i lost about 3 hours of my life tearing down that gearbox and reassembling it trying to figure out why it kept locking the piston to the rear on full auto and the only way to set the AEG back to ready was to put the gun into safe to decompress the spring, every fffing shot on auto it would lock but on semi it worked fine ??

It was only when i pulled the piston out and placed it on my desk standing up in despair that i noticed that it was slightly longer than the original which may i add had its teeth ripped out by the gears (whose teeth also shredded) when my mate decided to use an 11.1 LiPo on stock gears.

 

[Adam3088]

Hi mate i am guessing this is for your SCAR-L?

I did some tech work on my mates WE SCAR and found the out of box performance a bit pants (around 280 FPS).

Yes i would say the spring also feels weaker than a M100 spring, it was one of the first things i changed in his gun when i upgraded it.

As for the piston what i will add is that the WE AEG gearboxes are very sensitive when it comes to the length of the piston, I replaced the original piston with the Mad Bull Alien Green one and could not for the life of me figure out why the gearbox kept locking up on full auto. It wasn't till i measured (with a digital micrometer) the Mad Bull one with the original one that i noticed the Mad Bull one was about half a millimeter longer, when i installed another piston about the same length as the original it worked fine.

But yeah, clean the screw and screw hole, add loctite, put it back together, let glue dry and test fire a few shots.

Very odd! I noticed that the tappet plate is a non standard length as well, hate proprietary stuff..

Think the zci piston is ok, had it on full auto for a while and its not locked up as of yet...

I'll drop the bearing in the piston for now, will keep the new spring guide in as the stock one was a bit naff.

Actually thinking about it I can just remove the bearing from the guide, that'll do the trick.

 

[Adam3088]

Rebuilt the gearbox, all appears to be working correctly now.

I had to clip the spring in the end, even with a bearing removed I had to compress it so much it was bloody impossible to get in. Used a dremmel to hack off 3 coils and then ground the end flat.

I reckon it's shooting 310-320ish now, but will have to wait and see until I can actually chrono.

Sounds a bit whiney still but that may just be from the pinion as it's stock and not a brilliant fit with the new gears.