Air seal problem- loss of fps
 

Ok, so I upgraded my sig 552 with the following compression parts:
-System reinforced piston
-Systema reinforced piston head
-Guarder steel cylinder head
-Guarder air nozzle for sig series
-KM TN inner barrel

For a spring I am using a PDI 170% and for the first few days after I upgraded my gun it was shooting at the propper fps which was about 410. Recently it started shooting much lower, at about 300 fps, so I took the gun apart and started checking out my airseal. I'm pretty sure that I am loosing a lot of air between my cylinder head and my nozzle. I tried first putting my finger over the cylinder head and pushing the piston in and it was pretty much a perfect seal, but then when I tried to perform the same test with the air nozzle installed I could see that a lot of the air was leaking out around the base of the air nozzle. I tried lubing the air nozzle where the air was escaping but that didn't really help. I also tried it was the stock TM air nozzle and I was still losing a lot of air in pretty much the same area. So I guess what I am wondering is will I have to buy a new air nozzle or is there some way that I can stop the air from leaking out around the base? Also is there any other spots that I should be checking for leaking air such as around the hopup unit? If so how do I do that?

Well I'm stumped, any help would be much appreciated

How's your compression if you plug the tip of the cylinder only (remove nozzle)?

humm

duh, sorry. Assessing leaks can be difficult by plugging things with a fingertip. How serious is the leak? It's not necessary to get an airtight seal, but the leak shouldn't be too strong. Is the oring inside the Guarder nozzle broken?

its a pretty serious leak, we're talking around a loss of 100 fps, ill take a look at the o-ring

well, all I'm saying is that don't fixate only on the nozzle-cylinder leak. Look for other problems like a damaged hop up sleeve or a badly aligned hop up assembly. It's difficult to say how large the nozzle-cylinder leak is in text. If the oring on the guarder nozzle is broken, that would result in a large leak. If you have a poor nozzle-hopup fit, that can also cause serious problems. You could also have mutiple problems.

ya i understand what you saying, is there any specific way i can test to see if there is infact a leak between the hopup and the nozzle? I appreciate your advice, thank you.

Try this:

-flip your gun upside down
-drop in one bb into the mag inlet
-fire gun in a safe direction
-put your hand over the mag well and feel for a strong puff of air

If the nozzle does not seat into the hop up you may feel a very strong blast of air. Small puffs are normal, but a strong leak is not. Inspect your hop up sleeve carefully for tears.

ok cool ill give that a try, i know for sure that the hop up rubber has no rips or tears

Try to lube the hop-up then swab it out with the cleaning rod and a quality paper towel. You may have gotten some cylinder lube on the hop-up sleeve and this ruins the airseal or the system.

Seen it dozens of times. An M120 shoots 265 FPS before clean and re-lube, then shoots 400 after. Hmmmm.....

Check for leaks:
1)Nozzle- if leaking try to clean and put 50,000wt silicone oil or check if airseal nozzle you "bought" is design for that specific gun(hehe).
2)Cylinder head Oring, plug the cylinder nozzle without airseal nozzle put it in a bucket full of water for leak test, if there is leak, clean nozzle,ckeck oring if okey, if okey, put 50,000wt silicone or put a teflon tape before placing the oring.
3)Check hop up rubber,clean,to take out any lube material,this is a culprit most of the time,and if there is a rubber crack, replace.
4)if all are okey, check hop assembly, this is the worse part if there is a crack in the opening you got to replace this or else we might wonder why everything is okey or all has been replace but results still the same, this part is the culprit if everything you do and still doesnt work out.