very weird problem: 3 mechboxes with 100 fps loss
 

Heya all

I have these 3 mechboxes (all ver 3, 1 MP5k, 2 Steyr AUG ) I have upgraded with

-bearing spring guide
-SP 100 and 110 springs
-torque up gears on the 110

-all piston heads are ventilated
-AUG cylinders are stock
-systema unported cylinder on the mp5k
-guarder cylinder head on the 110 mechbox
-mosfet on the 110 mechbox


And they basically all are under the expected FPS, giving me around 240 fps each.

Everything is perfect mechanically, so I suspect problems of air sealing.
-rubber sleeves are good
-I have 2 barrels for the AUG and they BOTH produce that low FPS with both mechboxes, so the hop ups are probably not the guilty ones.

The 110 mechbox gave me more than 420 fps in the past with the same parts and different spring, so really I don't understand.

here are the places that could be bad airseals:

-cylinder heads ( mp5 is stock, aug 1 is stock and aug 2 has a guarder AUG head that is not very old)
-piston heads (the mp5 O-ring is BRAND NEW though)
-nozzles ( I ordered new nozzles but the ones I have are correct)

more than 100 fps loss: wtf ?

the only possible solution I have thought of until now is me being victim of a curse.
anyone has any idea ?

thx!

Did you remember to install the brass sealer/stabilizer ring in the hopup chamber when you replaced the inner-barrels?

Maybe the springs are lemons?

The stuff you have one are right, it's really weird. How about the battery?

yes, but I will check if it's properly mounted thx


brand new springs from UN company.
and unless they had them in stock for six thousand years...

mm mechanical chain from battery to sector gear is flawless.
I forgot to mention motors are EG1000s but I'm not sure that matters.

Did you check the compression in the cylinders?

good question:
checking the mp5 made me change the piston head's O-ring.
I remember checking the AUGs before putting the mechboxes back together, I don't recall any problem.But I wouldn't be 100% sure that the seal will be perfect in any situation...

one more important detail I forgot:
sometimes the AUG misfired recently:
-misfire
-2 bb go out the next shot.

it did that a few times...
mmm maybe the O-rings are dead.

Just had a similar problem recently. Took apart the hopup and put it back together and put the barrel back together, and it feeds now.

Silly thing, but its worth checking if the springs are installed backwards. Everyone does it at least once, and its so simple that few think to check.

If you're talking about the main spring, the FPS difference between it flipped one way versus the other is negligible. Something like 5 FPS. It wouldn't cause these types of problems.

My money is on the hop-up bucking being misaligned... but I don't see how this could happen on 3 different guns though.

For the MP5K, if it has a stock length barrel you really need a ported MP5K cylinder for it or you'll loose a lot of FPS.

Jimski, may I ask how many guns you've upgraded before? Are you putting the tappet plate on the nozzle correctly? Tested that the piston moves freely on the piston rails? Done a compression test with your finger like others have mentioned? Check the Guarder cylinder head as well, they were defective a while back and you had to build up material under the o-rings to make them seal properly.

the mp5k has a silencer with a barrel inside, the whole thing should be around 30 cm.

You may: I've upgraded those guns with different configuration, less or more powerful, and never experienced anything that problematic.They all worked perfectly at one point...

I think so.it's hooked together.

yes.

yep! it was convincing at the time.

ahhh that's interesting thanks

That's only a 30fps drop maximum.

seriously though, how do you drop 130 fps, even with a mediocre air seal ?

broken nozzle/craked nozzle

dead oring on piston head/cylinder head.

hopup rubber is chewed up/torn

too much grease/oil

dirty barrel

retard spring.

any combination of these WILL result in fps drop.

I had a 250fps drop (150 instead of 400) on an AK before, because the ICS gearbox shell was ever so slightly misaligned with the hopup unit. Replaced it with a Cyma shell and it was good to go... don't know if that helps, but big FPS drops can be had, much more then 130fps.

I've personally seen drops of 60fps from that. I believe there is a difference in the fps drop between different brands and ratings.

ok thank you guys, this is helping me a lot.
keep it coming!

interesting, I wonder if the sloppy AUG system can bring such problems.probably :D


ok I will check the grease factor also, I wonder if they are spewing grease.

With the grease thing, make sure that there is just enough to slightly coat the gears and the inside of the cylinder. Barely any is required in the piston and tappet plate slide areas. Most stock guns come with way too much grease on the gears, but too much grease would not result in that much of an fps drop.

With the mech box alignment, this usually does not affect an AUG. It can make a huge difference in an AR, but the AUG mech box either fits or it doesn't (unless the plastic insert plate is loose). Check to make sure that your inner barrel is not sticking (should move freely). Also, make sure that the outter barrel has no play (in and out) from the AUG receiver, and make sure that the upper and lower receiver have no play. Any excessive play in either of these places will cause air loss at the hop up, and could also result in the mis fire you described.

SHA DO

Go here for AUG info. You'll need to sign up but it's worth it.

http://www.arniesairsoft.co.uk/forum...64&hl=helpdesk

Seems like you can have the mechbox break loose and start to migrate backwards compromising the seal and dropping the velocity. Fixes for both the minor and the major types of this failure are listed in the thread.

Did you do a compression test on your cylinders? Hold you finger over your nozzle (nozzle installed, maybe even tappet plate as well) and push the piston with your other hand like a syringe and see if air leaks.

Put it into a tub of water and see where the bubbles come from.

U said they are ok mechanically but id check the bushings.

My old CA G36C had a deformed bushing once that brought the fps down to like 95ish.

that was running stock so check that if you haven't already.

thank you guys!
I did compression tests but I will redo them when taking the mechboxes apart.

I don't think it's anything mechanical since it's been checked recently, I'd go for the sealing problem.
Although it could actually be something mechanically slowing down pistons.
I'm waiting for some parts, and I'll post comments asap when I get new results.

well its not something most mechanics would notice right away.

I was at Ashbash when it was in California and the airsoft extreme tech didnt notice it but the redwolf tech did.

Check your actual hop-up body.

I had to change one in my friend's AUG because there was a little, barely visible crack in a corner where the barrel clip goes.

Changed for a metal one (and had to modify it to fit properly, better with a stock one).

voila!

If you have spare time this week-end, you can drop to my place. My AUG is currently shooting 398fps on every shot. With that, we can surely find where is the trouble.

Good thing the AUG is easy to disassemble.
Have you tried another known good hop up packing? Did you try a known good nozzle; some aftermarket nozzles have little o-ring(s) on the inside diameter to help seal too.

I had a problem with a Marui G3 that I was scratching my head on for a while. It was set up with Guarder FTK and a PDI 170. Clocked it with the Guarder Speeder 2000 at just over 290 fps w/ 0.20g bb= WTF? Went with an Action o-ring nozzle and Guarder Clear Hop Up Packing and got 345 fps with 0.25g. I had to clock it with 0.25g bbs because I had run out of 0.20g.

Anyways, my two cents on the bit. Didn't think that those 2 components made that much of a difference.

thanks a lot Kosmos and Smurata1, I think your suggestions are close to my problem's solution, but I can't really be sure exactly how:

Sooo tonight I added a metal hop up.
the metal ring can't really fit between the hop up and the barrel; how critical is it exactly ? I stuffed it as deep as I could...
other than that, at the barrel level the seal seems ok...when I blow into it :)

I also changed the cylinder set for a systema one on the first mechbox.
The cylinder head is suprisingly loose in the cylinder.it is ventilated.
The spring is not reverted (linear end front,compressed nonlinear end towards shooter)
aaand I added a metal nozzle with the O-ring.

it still shoots 249 fps!
:(

I checked the seal with the bucking when the barrel is mounted, it looks uber-perfect.
Could there be a leak at the junction mechbox-hop-up ?

soo here is where I am now:

it is either:
-the piston being too slow ( bad spring, bad slide)
-air leaking from the mechbox/hopup junction (mechbox and body related), from the nozzle/bucking junction (assembly related), from the hopup/barrel junction (hop up body related) , or from the piston O-ring (brand new and bought as a set with the cylinder).

I just changed the O-ring on the piston head, compression is gold, ventilation to avoid suckback works.
I am wondering about cylinder porting and barrel length now.
fps test tonight.
cheerz

ah ah
tested mechbox 1 with short barrel, got 131 fps at first shot and around 240 afterwards (should be around 340 lol )
after that something went krrr krrr krr so I have to check it out again.

so far each testing has brought me even less fps than before :)

tonight I'm testing mechbox 2 (should be around 380 fps) with both barrels.

next game I'll probably just bring my inner barrels and blow BBs with my mouth, sarbacane-style.

seriously I have no idea what is wrong, everything is perfect.

You should send your AUG to me and I'll fixy fixy. :D

Oh I had the exact same problem that you're having. You should check your shimming because what's happening is that the gears are too loose inside the mechbox and when you pull the trigger the gears will give way and spin in reverse letting the piston shoot forward before it is pulled back all the way (hence the low fps).
Check if that works for you.

ooooh good observation I will see that tonight thanks a lot dontask!

I had a 350 FPS loss on my VSR-10 because the cylinder was dry... Spray some silicon lube in there!!

Your fps problems are probably related to the cylinder head and nozzle. I had an aug set to me from another gunsmith who had the same problem and could not get it working. The compression on the cylinder head and piston were great. Compression including the nozzle was great aswell but for some reason the mixture of parts did not work with the stock tm hopup unit. So what I ended up doing was swapping the upgraded parts back to stock tm and the fps was where it was supposed to be. I would suggest narrowing down your problem by leaving the tm cyilnder head and nozzle in one of the aug boxes and testing it.

Don't forget to check your piston! It could very possibly be a stripped piston as well.
But its probably the shimming because it's kind of rare for three mechboxes to simultaneously strip their pistons at the same time lol.

update:
the piston is not stripped.
the short barrel got a bb stuck in it twice when I tested hence the krr krr.

I reshimmed the gearbox and got 249 fps with the long barrel (46 cm)
battery is recharging now...(9.6v 2000 mah)

Cleaned the barrel at all?

the barrel is clean, it was stuck in the bucking.
I re-assembled the hop-up, tests tomorrow.

Sooo, new tests brought some clarification:

I justed tested another mechbox in the AUG with both short and long barrels, and I get the expected amount of fps (350-ish)
So it's definitely a mechbox related problem.

I changed the spring and guide back to stock on the faulty mechbox and it's still stubbornly giving me 250-ish fps.
apart from that it's working like a charm, and I'm not getting any barrel issue anymore.

I tried every part combination I could.
I won't exceed 250 fps, ever, even with different springs. :(
I fail.
this gearbox is cursed.
btw systema bore-up kits are crap, don't buy them.
EDIT: actually they're not, the O-ring just needs to be stretched.

Like I said, gimme gimme, fixy fixy! I've worked on my AUG a bunch.

Or get thyself to a local doctor.

sorry guys, I fix my stuff myself, that's the whole point :)

problem solved !
-not enough grease on piston heads and nozzles (between nozzle and cylinder head)
-systema O-rings need to be stretched a little bit before use.
Using size-up o-ring doesn't work :D

thanks to all!
special thanks to Amos and Crunchmeister for the good advice :)

ASC wins.

http://media.ebaumsworld.com/mediaFi...855/861035.jpg

No problem dude. Always glad to pass on what I've learned along the way. I had similar issues in my M15's mechbox when I swapped for the Systema silent piston & cylinder head sets about 6 months ago. I couldn't figure out why I was only shooting 320 fps with a Prometheus MS110SP spring. It was Illusion who replied to my thread telling me that Systema rubbers had to be stretched to work properly and put me on the right track. Now my gun shoots 385 pretty consistently with .2s, and I couldn't be happier with this gun.

Once I realized that, I started studying how the piston head / ports / o-ring and worked together in the cylinder to give good compression, it all made sense. It's a learning process that can be quite furstrating at times, but once an understanding of something hits home, it just seems so easy and obvious.

But anyway, glad to hear that you got you issues worked out.

I just think that bass players are superior beings.

Well, there's that too...

lol

updatez:
I still have 2 gearboxes that both use a SP100 spring with readings around 250 fps.
(both ver 3, one is AUG, the other is mp5k, both unported - cylinders, heads and nozzles are new.)

just to make sure I tried one with a 400 fps spring, and got my f-ing 400 fps right away.Switch back to SP100 and boo, 250 fps again.
since no spring I know of is rated for 250 fps, it can't be a spring labelling mistake.

I am guessing that this powerful spring is creating a wider spread of the O-ring, thus making it work properly with a 400 fps acceleration, and improperly with a 340 fps acceleration.
What I'm wondering is why, since both O-rings look healthy and are the right diameter...

Well, in the case of your MP5K, a non-ported cylinder is too much even for a ~300mm barrel. You're not getting the max efficiency out of your spring. You should be using 3/4 (actually around 300mm) or 4/5 (360mm plus) port, according to Arnies.

but I get exactly the same results with this cylinder, is the port size wrong?
- the barrel is around 30 cm long-

http://i225.photobucket.com/albums/d...6/92c8717c.jpg

That looks like a 1/2 port for stock MP5K length barrel. It would likely give you too little air.

ok thx,
also I forgot to mention the piston head is ventilated.

Dude, if a 400 fps spring shoots 400 fps in both your guns, and the other spring only shoots 250,

IT'S THE SPRING!

Get a new one!

I have two brand new SP100 springs and they both give 250 fps with those mechboxes.
and I want 350 fps max, it's not like can just shove a 400 fps spring in them and be done.

I don't think its the springs.

If the 400fps spring is working at the intended fps and consistent, it's most likely your other springs.

+1 women and booze to the rythym section first.:cool:

tonight I try a custom spring, we'll see :)


of course :)

ok so tonight I tried with a SP120+ spring, and I get anywhere from 337 to 406 FPS.

I'm pretty sure it's not the spring, there's something about inconstant compression somewhere.

I question the junction piston/piston head.
I will test a piston head with bearings this week...

apparently I can get a high fps with a strong spring, but I get maximum 250 fps with a SP100, and as low as 190 sometimes.

can I get barrel suck even with a ventilated piston head?

Barrel suck doesn't exist.

ok so what then?

okk so I found the problem on the MP5k but I don't know how to solve it:

AEG ready to shoot :the nozzle is set on the hop sleeve, the is BB in the chamber-part of the barrel (just before the hop-up notch)
the thing is that at that point you can blow air inside the nozzle and it just flows around the BB through the front end of the barrel.

if I cap the front end, seal is good.

Air isn't leaking from anywhere I can tell, but still half of the power will be wasted because it just flows around the BB to the front of the barrel.
It feels like a super un-tight barrel.
what could I possibly do?

question: is it normal that the bb sits after the hop-up sleeve's rim?

BB should be inside the hopup rubber before it fires. The nozzle pushes up against the rubber [as it pushes the BB into the rubber] and makes a seal, then fires. Maybe try a new rubber?

Is your hop up turned on? I've had weird problems with fps/misfeeding if the hop up is turned all the way off. Just a suggestion.

I'v added a tightbore barrel and it still does not give more than 250.
I'm tired of this piece of shit.
I suspect the body and the hop up unit to be misfits, I'm pondering wether I should try with other ones or just stomp ragingly on the aeg and burn it with gasoline.

I think you need to give it to me for cheeps :D

not gonna happen :D

You may not have the right piston head to match the spring. Some of the systema piston heads need a high fps spring to properly expand the oring during the compression. If you have a weak spring the oring dosent get a proper seal. That is the only thing aside from the spring being mislabeled.

You don't need 350 fps... considering your so trigger happy :p

Alright... after a few months... maybe you will consider dropping by my place (considering that it's 15 minutes from your place...)

that is exactly what I am thinking.
but I still should get a high fps once in a while, shouldn't i ?

Dude, it's been a months and you haven't solved the problem. Take it to a gundoc!

That piston head thing apply only if you are using a bore-up setup.

You could have mistakenly used a normal bore piston head, but the seal is so bad that you would have noticed right away.

Possible choices right now:

Broken cylinder head (mine had an hairline crack running from the "tube" to the bottom, and I lost over 100 fps)
Broken piston head (same thing happens)
Broken nozzle (again)
Broken mechbox
Craked/misaligned hop-up chamber
Ripped/twisted/torn hop-up sleeve

To test all these, you would need a complete working mechbox (unopened at first).

If the new mechbox works as it is supposed, you can sort out all the hop-up section.

Then swap the working parts with the parts from the non-working mechbox (one at the time, then re-assemble the gun COMPLETELY).

If you still want to do it, good luck. Otherwise, you know how to contact me.

you just don't get it, do you?


mm sometimes I wonder, systema NB cylinders are really wide inside.
will check

will check

nope, nozzle is metal and its action seems ok.

will check

I bet there's definitely something with that.will re re re recheck, more.

nope, it's new.

thanks for the input! I know I'm stubborn :)

If you have a Deepfire metal nozzle, there is your problem.

I had to remove one from a G36C that had FPS/feeding issues.

Installed the stock one, and VOILA!

ah??
interesting though I don't really believe...I've had that pb with both nozzles.