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welcome to a new AIRSOFT REVIEWS HD episode
this not a review but a technical video
and in this episode we will talk about the air compression in a AEG
lots of my friends on facebook asked me for help
as they had the same problem of a major fps drop
this problem has to do with the bad air sealing inside the upper part of the gearbox
the bad air sealing in the upper part of the gearbox (cylinder area) leads to air loss and fps drop
many of you tried to solve their fps reduction, by installing harder springs
but still the could not output the factory fps rate
in this episode i will explain you as simply as i can, why this is happening
and what can you do to solve this serious problem
for display purposes and only, i will use my G&G L85A2 upper gearbox
i will disassembly it so i can get the cylinder set, the piston
as well as the nozzle
and i will use them to demonstrate what can it go wrong in your airsoft gearbox
before that, you can see the G&G L85A2 review on the top right of your screen now
or you can click the link on the videos discription
so i will unscrew this bolts on the upper receiver
and we will gain access to the insternal parts of the AEG gearbox
i have removed the gearbox shell, and here is the air production unit
the system aparts from the cylinder, the cylinder head, the nozzle, the piston w/ piston head and the tappet
i will remove the tappet plate spring
and i will keep on my hand only the air compression unit
as you can see the L85 has a long cylinder
i will remove the piston from the cylinder
between the piston head and the piston there is a spacer so it can cover the long cylinder
this is because it doesn't have a 19 teeth piston
the spacer will leave the piston in the right engaging position so the sector gear can pick it up correctly
the G&G L85A2 sector gear has 19 teeth
this L85A2 has a plastic piston head
as it comes in the most stock AEG gearboxes, even in the most expensive AEG's
nowadays there are some chinese made pre-upgraded AEG's
on the piston head there is an o-ring
this o-ring can be removed from the piston head
this o-ring is the most important part for a good air sealing
this o-ring will close the gap between the piston head and the cylinder
bad contact between the piston o-ring and the cylinder will lead in serious air leak & bad air compression
so if you have fps drop, this is the first place you have to look
if you have changed the o-ring, be sure that it fits perfectly on the cylinder
if there is bad compression caused to the o-ring, the o-ring can be worn down from use
so let me now show you how you can easily check for air leaks
if there is a good air seal between the piston o-ring, the cylinder
as well as the cylinder head and the air nozzle
and we close with one finger the air nozzle hole
the piston should not go down to the cylinder head as we push it in the cylinder
as you can see the piston will not stop
check it many times, because the piston is not perfectly lined in the cylinder
as it happens in the gearbox (by running on the piston channels)
when i try to push it in, i feel a low resistance but the piston should have stop approximately at the half of the cylinder
you also listen the air leaking out of the system
to be honest the most of the air leak comes now from the nozzle
in many cases of AEG i have upgrade, there was a serious air leak between the cylinder head and the nozzle
i will remove the air nozzle and i will retry the test without it
as you can see, there i much better result in this test
the piston will stop in the middle of the cylinder even if i apply very hard pressure
it seems that in this case, the piston o-ring fits perfectly in the cylinder
but the air seal between the cylinder head and the nozzle is not good
the air nozzle is woobly on the cylinder head, and even if it has a o-ring it does not fit well
so there is a good air leak in this point
if you have air leaks in this point, you can get a nozzle with o-ring
this is an SHS aluminium o-ring nozzle
so it is the best you can get for this part
but the cylinder head is stock
always try to match parts of the same company
because with this way you will have the best fit in all your parts
if i get an SHS L85 cylinder head i am sure i will have a perfect air seal in this point
i will recommend to change you cylinder head and air nozzle to get some fps in a very low cost
you can do the same with the piston head
but i think that there is no need spending money for that part
i will show you now a quick tip of how you can increase the air seal between the piston and the cylinder
first of all take the o-ring with hands or a small screw driver from the piston head
press the o-ring from here and from the other side pull it up
and the o-ring will get out of the piston head
i will show you now how you make this o-ring fit better in the cylinder
take the o-ring and place it on the cylinder from the outside
it will be hard but just stretch it up
this modification is known as the strech o-ring mod
with this action, we strecth the o-ring to increase a bit the diameter
if i remove now the o-ring, the o-ring will return to its normal size
we have to apply some immidiate heat on the o-ring so it will keep this size (or a bit smaller than that)
i will use a lighter to apply heat on the o-ring
heat up the o-ring but try not to burn the plastic
turn the cylinder continiously so the heat will go through all the o-ring
we only need to increase the temprature of the plastic so it will change the final diameter
let it cool down and place it again on the piston head
as you can see the diameter of the o-ring has increased a little
and this is what i need so it can fit perfectly on the cylinder cell
after the stretch, it will be harder to fit the piston in the cylinder but be patient
lets retry the air seal test
look the result, the piston stops and even if i apply more power it want move
that means that just with the strech mod, the air seal is much better
you can feel the better fit even by the friction in the piston movements
you can also increase the air seal
by applying some teflon tape on the cylinder head
i have already done this to my L85
the tape covers the factory o-ring and provides a better air seal between the cylinder head and the cylinder
if you do that mod, you want have any air loss from this point
with this modifications that demands only work and no cost
we can increase the air seal
and in combination of a good nozzle (or/and cylinder head)
the results can be very impressive
so if you have a major fps drop
before you will get expensive parts and extreme modifications
like harder springs, gearsets, high torque motors etc
that will cost you too much
try to check the air seal
also i will make another episode where we will talk about the air seal of the hop up/barrel units
until then check my videos for the hop up assembly/disassembly
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