m4 problem

matty1994

Ok im not a newbie at working on guns but this problem has shunned me, ive put a brand new g&g gearbox into my m4, ive done no internal work to it, and i put a new gaurder hop up unit with g&g green rubber into it aswell, but for some reason the gearbox is unreally loud, has an m100 spring in it, like its a proper bang that it makes, secondly the fps is really low around 160fps and will only shoot say 15feet, ive checked that the nozzle is the correct length and it fits right in against the lip of the hop up rubber giving a good seal, and i dont know where im loosing compression, i have a brand new piston and piston head which ive tried, and gears and piston head and cylinder but to no joy, any advice or help anyone as im looking at getting another m4

.K.A.L.I.M.A.

What type of cylinder do you have?

I was recommended a type-C for a 363mm inner barrel, plus a new SHS M90, and I got a low FPS reading (240-250FPS w/ .25g) and somehow a quicker drop in range. Switched back to a full cylinder, and my range had increased to a normal state, not sure on FPS though.

matty1994

.K.A.L.I.M.A. wrote: »

What type of cylinder do you have?

I was recommended a type-C for a 363mm inner barrel, plus a new SHS M90, and I got a low FPS reading (240-250FPS w/ .25g) and somehow a quicker drop in range. Switched back to a full cylinder, and my range had increased to a normal state, not sure on FPS though.

Im using a type c with a 363mm, its something internally thats not working right, ive replaced everything internally and still the problem persists:/

DeBurca

If the seal between piston O-ring and cylinder wall is good and just because you have fitted new parts does not always mean the all is 100% air tight then I would check the seal between cylinder head and cylinder
If that is good I would then have a look at the Air-nozzle, check the fit between air-nozzle and the brass pipe coming from the cylinder head to see if it a good fit with little or no wobble and it should be able to slide freely while allowing no air to escape between the two
Also check that the tappet plate moving freely in the gearbox shell as if there is any excess tightness it could be slow in forming a proper seal with the face of the hop-up rubber and you could be losing compression there

An easy way to check the above is to turn your M4 upside down without a mag and fire a few shots while holding the magwell close to your face and if you feel any air escaping then your problem is in that area

matty1994

DeBurca wrote: »

If the seal between piston O-ring and cylinder wall is good and just because you have fitted new parts does not always mean the all is 100% air tight then I would check the seal between cylinder head and cylinder
If that is good I would then have a look at the Air-nozzle, check the fit between air-nozzle and the brass pipe coming from the cylinder head to see if it a good fit with little or no wobble and it should be able to slide freely while allowing no air to escape between the two
Also check that the tappet plate moving freely in the gearbox shell as if there is any excess tightness it could be slow in forming a proper seal with the face of the hop-up rubber and you could be losing compression there

An easy way to check the above is to turn your M4 upside down without a mag and fire a few shots while holding the magwell close to your face and if you feel any air escaping then your problem is in that area

Ive done all that everything is air tight, i have a nozzle with a seal, and have it firing properly now again but im only getting 260fps with a m100 spring:/

DeBurca

Is it a standard G&G M4 gearbox or a G&G pneumatic M4 gearbox ??????????????

T4RGET

matty1994 wrote: »

Ive done all that everything is air tight, i have a nozzle with a seal, and have it firing properly now again but im only getting 260fps with a m100 spring:/

you definitely have an air seal problem. Alternatively your tappet plate may be broke. It could still be in a really awkward position allowing it to pull the airnozzle back and let a BB in but i would double check it.

If you've ever taken a GB apart i suggest doing that and taking the cylinder head and cylinder in your hand. Cover the cylinder head with your hand (where the air nozzle sits on) and push the piston into the cylinder as fast as you can, if the piston just slides into it with no resistance then it just has a crap air seal. If the piston resists a lot it means you have a good air seal and the problem lies somewhere else. The harder the piston is to push down the better the airseal and if you doesn't budge at all you have no leaks in that area.

Just make sure you push the piston into the cylinder as fast as you can, you want to replicate the force of the spring pushing the piston.

Like Deburca said check if you have a pneumatic G&G box in the receiver, the air loss could be coming from the hole on top of the gearbox for the pneumatic action. Air loss can come from here if the blow back is disabled which may also cause the loud noise.

EDIT: If the piston does slide into the cylinder without resistance it means you need a different piston. I just read there that you replaced the internals so it could be a compatibility issue

matty1994

T4RGET wrote: »

you definitely have an air seal problem. Alternatively your tappet plate may be broke. It could still be in a really awkward position allowing it to pull the airnozzle back and let a BB in but i would double check it.

If you've ever taken a GB apart i suggest doing that and taking the cylinder head and cylinder in your hand. Cover the cylinder head with your hand (where the air nozzle sits on) and push the piston into the cylinder as fast as you can, if the piston just slides into it with no resistance then it just has a crap air seal. If the piston resists a lot it means you have a good air seal and the problem lies somewhere else. The harder the piston is to push down the better the airseal and if you doesn't budge at all you have no leaks in that area.

Just make sure you push the piston into the cylinder as fast as you can, you want to replicate the force of the spring pushing the piston.

Like Deburca said check if you have a pneumatic G&G box in the receiver, the air loss could be coming from the hole on top of the gearbox for the pneumatic action. Air loss can come from here if the blow back is disabled which may also cause the loud noise.

EDIT: If the piston does slide into the cylinder without resistance it means you need a different piston. I just read there that you replaced the internals so it could be a compatibility issue

It wasnt an air seal issue, i had checked ive sorted the problem now, it was the cut of lever, it allowed the sector gear to turn even when the trigger was released, sorted that out and now i have it firing at 310fps, thanks for all the help though:)

DeBurca

Sorry I don't understand how can the cut of lever effect the FPS ????????????

matty1994

DeBurca wrote: »

Sorry I don't understand how can the cut of lever effect the FPS ????????????

Because it never stopped my sector gear from stopping which allowed the tappet plate to pull back the air nozzle reducing the seal and the huge drop of fps

T4RGET

matty1994 wrote: »

Because it never stopped my sector gear from stopping which allowed the tappet plate to pull back the air nozzle reducing the seal and the huge drop of fps

that makes zero logical sense but hey it's airsoft glad you got it sorted mate

matty1994

T4RGET wrote: »

that makes zero logical sense but hey it's airsoft glad you got it sorted mate

Its hard to explain but its the first time its happend to me haha, its all sorted so im happy now:) and thanks:)

Leftyflip

matty1994 wrote: »

Because it never stopped my sector gear from stopping which allowed the tappet plate to pull back the air nozzle reducing the seal and the huge drop of fps

...Yeah, doesn't happen. Going by that logic if you were firing full auto, nearly all the shots would be really low.

matty1994

Leftyflip wrote: »

...Yeah, doesn't happen. Going by that logic if you were firing full auto, nearly all the shots would be really low.

Well thays it, the gun was kinda firing full auto but not exactly full auto, it would stop a quater way through the second stroke