Compression Problem

thegrayson

After having some problems with a drilled cylinder I was supplied with a new cylinder(ported), spring(90) and cylinder head with air nozzle by ASG(many thanks) but after re-assembly I can't get the AUG to fire worth a damn. Its so bad some of the shots don't even regisiter on a chrono. The cylinder head is a tight fit, the piston head is so so, hard to guage its seal with ported cylinder, I'm not sure about the air nozzle.

I've only repaired about ten airsoft guns so far, so my lack of experience is against me. Without buying a number of parts where should I begin?

Inari

As far as I know the AUG needs a non-ported cylinder. I'm not certain on that, having never had to open one up, but that's just sticking in my head.

PS: Ported cylinders should have the port as far away from the cylinder head as possible, and you'll still be able to test compression as it will kick in once the port is clear.

thegrayson

The original drilled cylinder was ported and the fps was right on the limit. ASG supllied a ported cylinder as they said the JG made AUG comes with the ported cylinder by default. I might try taping over the port to see how it improves the problem. If not I could end up ordering an un-ported cylinder and an air nozzle with a seal.

Inari

Right, if the gun's original cylinder was ported, then it should be fine.

Grease the inside of the cylinder using cylinder grease, and lube up your piston head O-Ring. You can add PTFE tape around the piston head, which helps buff it out too. You can do the same for the O-rings on your cylinder head. This should improve compression.

Are the parts you were given definitely the right ones? We had an AK in for repair a good while ago that just would not fire over 200fps, no matter what. It turned out that during maintenance the lad had replaced the air nozzle with one that was 2-3mm shorter

thegrayson

The old and new air nozzle are the same. It doesn't seem to matter which I use. Everything is already well lubed. Where do I add the ptfe tape on the piston head? I don't want to interfere with the o-ring being able to expend as air passes through the head.

Southern Dandy

thegrayson wrote: »

The old and new air nozzle are the same. It doesn't seem to matter which I use. Everything is already well lubed. Where do I add the ptfe tape on the piston head? I don't want to interfere with the o-ring being able to expend as air passes through the head.

Take off the O-ring on the piston head and add the PTFE to the groove where the O-ring sits, not too much, then put the O-ring back on as normal.

Read a few places putting the ptfe over the whole piston head but I don't wreckon that a good idea some how. Silicone grease not oil will cause the O-ring to expand a bit if you wana try that.

lux-et-veritas

thegrayson wrote: »

After having some problems with a drilled cylinder I was supplied with a new cylinder(ported), spring(90) and cylinder head with air nozzle by ASG(many thanks) but after re-assembly I can't get the AUG to fire worth a damn. Its so bad some of the shots don't even regisiter on a chrono. The cylinder head is a tight fit, the piston head is so so, hard to guage its seal with ported cylinder, I'm not sure about the air nozzle.

I've only repaired about ten airsoft guns so far, so my lack of experience is against me. Without buying a number of parts where should I begin?

just a thought but have you tried a new piston o-ring? its usually a BS 116 i think.... you can pick them up quite qheep online...

dinnybyrne

could be a problem with your tappet plate.check if the air nozzle is fully forward after firing by pulling it

dinnybyrne

if it pulls forward thats ur problem

BeardySi

Once you go over 400mm generally it's best to use an unvented cylinder.

An M90 in a full cylinder AUG with proper airseals etc should be chucking out just a shade under 1J.

In it's original cylinder it had a much more powerful spring don't forget...

Fit head to piston and cylinder head to cylinder. Insert piston fully. Cover the air nozzle with a fingertip. and try and pull back the piston. If its getting a good air seal you should have some difficulty doing this...

thegrayson

Thanks Everyone. Plenty to look at this evening.

maciek87

thegrayson wrote: »

After having some problems with a drilled cylinder I was supplied with a new cylinder(ported), spring(90) and cylinder head with air nozzle by ASG(many thanks) but after re-assembly I can't get the AUG to fire worth a damn. Its so bad some of the shots don't even regisiter on a chrono. The cylinder head is a tight fit, the piston head is so so, hard to guage its seal with ported cylinder, I'm not sure about the air nozzle.

I've only repaired about ten airsoft guns so far, so my lack of experience is against me. Without buying a number of parts where should I begin?

If they dont register on the chrono, than its really, really bad, so I really dont think it will be the compression problem.
Like said above: check your air nozzle tap. Sometimes everyone can forget about this little recoil spring....:rolleyes:
From what you said, it`ll be your solution.

Edit reason: I presume they dont roll out from barrell, yes? You did not mention about that, but if thats the issue, re-check the hop-up.

thegrayson

Dinny, the air nozzle doesn't pull forward after a shot.

Maciek, the spring on the tappet plate is attached.

Did find that the piston head seemed a little loose

Shame its too late to test fire it.

maciek87

Hi again,

Piston head seemed loose, or maybe 'o'ring on it...?
To screw the piston head tighter - look for the screw inside the piston where the spring goes (behind the piston head).

You can try to put your finger on top of the cylinder head, and try to move piston backwards and forward - see what kind of compression you`ll get.

If you`ll take couple of dry shots, to try to move air nozzle in the loading position (forward) and then press it by a finger - you`ll make sure the air nozzle circulates properly, as it should move freely backwards and back to the forward position.

Did you check the hop-up rubber already...?

thegrayson

The piston head itself was loose, I tightened the screw up again after putting some threadlock on it, I would have done this already after the spring change so I hope it doesn't work loose again. Compression seems good.

The air nozzle does move fully backwards and forwards, it does allow a bb to load, but the tappet plate does seem to catch a little as it travels back.

I have already checked the hop-up, the rubber is in good condition and it is working.

I won't knwo more til I test fire and chrono the AUG, it was too late last night to take it out the back, the neighbours might object to the noise.

SOCOM

thegrayson wrote: »

The piston head itself was loose, I tightened the screw up again after putting some threadlock on it, I would have done this already after the spring change so I hope it doesn't work loose again. Compression seems good.

The air nozzle does move fully backwards and forwards, it does allow a bb to load, but the tappet plate does seem to catch a little as it travels back.

I have already checked the hop-up, the rubber is in good condition and it is working.

I won't knwo more til I test fire and chrono the AUG, it was too late last night to take it out the back, the neighbours might object to the noise.

I know someone mentioned this already but line up your new air nozzle with the stock nozzle, I had weeks of grief buying several different nozzles and none of them worked, only the stock one! Try the tissue test, place a small ball of tissue in the bb loading port of the hop unit and pull the trigger, if it flies out, its your nozzle, btw I used a solid cylinder with a 509mm inner barrel

thegrayson

Got it working today, only 250fps though. I think an un-ported cylinder will do the job. Took the gearbox apart to seal up the cylinder with a metal foil tape I have and guess what? One of the trigger contacts has snapped :mad: and from looking about its not a contact that available to buy seperately and with the AUG being a little different a standard V3 switch doesnt do the job either. This AEG is giving me a nasty headache.

dinnybyrne

thegrayson wrote: »

Got it working today, only 250fps though. I think an un-ported cylinder will do the job. Took the gearbox apart to seal up the cylinder with a metal foil tape I have and guess what? One of the trigger contacts has snapped :mad: and from looking about its not a contact that available to buy seperately and with the AUG being a little different a standard V3 switch doesnt do the job either. This AEG is giving me a nasty headache.

what did you do to fix the problem?

Southern Dandy

thegrayson wrote: »

Got it working today, only 250fps though. I think an un-ported cylinder will do the job. Took the gearbox apart to seal up the cylinder with a metal foil tape I have and guess what? One of the trigger contacts has snapped :mad: and from looking about its not a contact that available to buy seperately and with the AUG being a little different a standard V3 switch doesnt do the job either. This AEG is giving me a nasty headache.

Man there is nothing worse than something that should be so easy ending up so complicated! Save yourself alot of agro and take it to a gun-tech and its out of your hands then and you have peace of mind that it will work! well hopefully anyways...

thegrayson

Erm, I taped up the ported cylinder and the AUG came in way hot So I've gone from dodgy due to a drilled cylinder, to not working, to 250fps, to 390fps. Guess I'll try a 100 spring instead of the 90 with the ported cylinder and see how I get on. This makes for a good way to learn the ropes.

Southern Dandy

thegrayson wrote: »

Erm, I taped up the ported cylinder and the AUG came in way hot So I've gone from dodgy due to a drilled cylinder, to not working, to 250fps, to 390fps. Guess I'll try a 100 spring instead of the 90 with the ported cylinder and see how I get on. This makes for a good way to learn the ropes.

I could be wrong like but shouldn't you be getting more that 250fps with a ported cylinder and a M90 spring? I thought you would have at least 280fps with that.

You must have a leak somewhere, and stupid question but is the ported cylinder in the correct position as in the port at the rear of the gearbox? I know its highly likely you did install it correctly but you never know

thegrayson

I was hoping that with the M90 spring I would get a decent fps. Took it apart, checked it again, still the same. I took a chance with taping up the cylinder, wasn't sure what to expect, 390 was a surprise. Have to admit, I'm curious as to what I might hit if I put the original spring back in.
Experiments aside, best way to get in and around 300fps....

THE MINDER

Not sure what length barrel is in the AUG but the cylinder volume should corrospond with the barrell length-as threadhead suggested if the barrel is 400mm or over you will most likely need the non ported cylinder-below that and you will need a ported cylinder-position of the port depends on the barrel length.Thats the first thing to ascertain- if its ported make sure that the port is nearest the back. Sort that and then do your compression test.You can do this with the cylinder/cylinder head/piston/tappet plate with spring/air nozzle all in place in one half of the gearbox-move the piston back and forward with one finger whilst keeping another over the air nozzle-you should not be able to push the piston forward.Socom correctly alluded to the length of your air nozzle-compare it to the original-if your new one is shorter you will most likely have an air leak there- try the old one-put a small bit of cylinder grease on the inside before placing on the cylinder head to help with airseal(it should move freely on the cylinder head).Airseal from nozzle to hop unit can be tested with the gun fully assembled by turning it over and putting a small piece of paper over the entrance to the hop unit in the magwell-dry fire th gun and the paper should stay where it is-if it blows off you may have a problem with the air nozzle or hopup bucking-check the bucking first. ALL after you get a replacement switch of course:)

BeardySi

509mm is a standard AUG barrel....

THE MINDER

Treadhead wrote: »

509mm is a standard AUG barrel....

Full volume unported cylinder required for sure.You got 390 with an SP90 so maybe an SP85 spring(Alternatively you can take a couple of coils off the SP90 but the former is a better option).

thegrayson

No need to replace the switch after all. Actually managed some tidy soldering, a first for me. I still find it very unusual that the default cylinder, as supplied by the manufacturer, is ported yet all other sources recommend an un-ported cylinder for the AUG. That aside, the plan now is to try it again with the original cylinder, then after payday order a new unported cylinder, I don't think my tape mod would stand up to much use, and a S85 spring.

One other small change I made was to fit a small foam pad on the inside of the plate that holds the gear box in place. I read that some people find that after awhile the gearbox isn't held in place properly leading to a poor seal at the hop-up. After fitting the pad, only 1.5mm, the AUG even sounds healthier on firing, maybe that in itself has improved my airseal.