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.