AEG compression issue

[Wepspec01]

So recently I decided to do a spring swap in my G&P M4 and royally screwed it up. Parts flying everywhere and all that. While I was re assembling it though I read that if you place your finger on the nozzle and manually push the piston through the cylinder it should eventually become difficult or stop with good compression. When I tried this, nothing like that happened at all. I may be missing something but it looks to me like it has a terrible seal. The O ring seems to be "floating" even though it doesn't look to be damaged at all. Is there something I'm missing? Would anyone have recommendations as to what upgrade parts are required to fix the problem if need be? (Cylinder/cylinder head/piston head)

Additional info- I'm running a 300 mm 6.03 Tight bore barrell

Thanks in advance.

[Kokanee]

Try disassembling your cylinder assembly. Lube the cylinder head oring with grease and place it back in the cylinder. Make sure your piston head oring is well lubed with grease. Reassemble and try again. If that doesn't fix it, maybe a problem with the nozzle seal.

But what I outlined above fixes 90% of airleak problems when I have guns on my workbench.

[Wepspec01]

Check. I'll give that a shot this evening. Could I trouble you for a suggestion on the best type of grease?

[RainyEyes]

People will give you different suggestions on lubrication. Personally, I use white lithium grease. It's generally inert, spreads heat well, but is difficult to find. I think Canadian Tires carry them, but their stocks are... iffy.

When you're doing your compression test, how hard are you thrusting? You need to thrust quickly and straight down, not along the sides. That way your piston o-ring will expand and hit the sides, hopefully creating a seal. As well, is your cylinder ported, because that is something to consider for better compression (in theory) depending on your barrel length.

[Wepspec01]

Originally Posted by RainyEyes

People will give you different suggestions on lubrication. Personally, I use white lithium grease. It's generally inert, spreads heat well, but is difficult to find. I think Canadian Tires carry them, but their stocks are... iffy.

When you're doing your compression test, how hard are you thrusting? You need to thrust quickly and straight down, not along the sides. That way your piston o-ring will expand and hit the sides, hopefully creating a seal. As well, is your cylinder ported, because that is something to consider for better compression (in theory) depending on your barrel length.

I was pushing fairly quickly yes, it just seemed to me that there was more space between the stock brass cylinder and the piston head. I've got some lithium grease that I can try.

[HKGhost]

I recommend using pure silicone grease for anything rubber and plastic, and high quality synthetic grease with working temps from very cold, to very hot for all metal parts. There are some grease with PTFE, it's a good additive.

[Kokanee]

Superlube http://www.homehardware.ca/en/rec/in...c74/R-I8640063

Or I use Schwinn bicycle grease for compression parts. Whatever you use, just make sure it's petroleum free.

[ThunderCactus]

Theres supposed to be a gap between the piston head and cylinder. As you push the piston forward, the air pushes the oring into the cylinder creating a seal. You have to push real fast to get it to seal. And LIGHTLY grease it, just a thin film. Overgreasing will cause leaks.
Test the piston head seal against the cylinder head only. There could be a leak between the cyl head and cyl, use a wrap or two or teflon tape to seal that. The o ring on your piston head could be bad as well.
Then test it in the mechbox shell with the air nozzle attched and in the FORWARD position. Air nozzles usually leak quite a bit, only way to guarantee a real good air nozzle seal is to buy 5 of them and pick the best sealing one.