"Perfect compression" test?

[MikeRarrmeh [64oz]]

I know that your suppose to cover your finger over the cylinder head nozzle and push the piston and if it doesn't go anywhere thats a good sign of excellent compression, but is it a bad thing if it can move doing the same thing with the air nozzle on?

[Riddick]

I would imagine so. Replace finger with BB. Many nozzles nowdays have inner o-rings to prevent air leak. Maybe yours is missing, worn or just never had one.

[Freespace535]

I was wondering the same thing, so I bought a nozzle with an inner o-ring, but the compression is still poor with it. I think you need to make sure that the cylinder head and the nozzle are the same brand if you want them to have the best seal - at least that's what I was told. A quick fix, although I don't know how long it will hold up, is to put some grease on the cylinder head's nozzle and some inside the air nozzle. It seals it fairly well, but just make sure that there isn't any grease that will be shot into the hopup/barrel.

[Nec]

I think you already know about checking compression with just the cylinder and the piston. by plugging the cylinder head with your finger and running the piston up and down in a somewhat fast motion you should get firm pressure resisting your push in.



The most common place for leaks while doing this compression check is the piston head O-ring, replace with a #14 O-ring available at Lowes or any other well stocked hardware store.


Next take the air-nozzle and place it on the cylinder head and clip on the tappet plate so that it looks like this:


Why do this? Because when the gearbox is put together and the piston is about to go forward the air nozzle is pushed although way out so that it can make good compression with the "lips" of the hop-up bucking. Running the piston up and down in a somewhat fast motion you should get firm pressure resisting your push in.

If you find a leak with the air nozzle the best thing to do is to find ether a tighter fitting air nozzle such as a TM or one with an O-ring inside.


If you don’t find a leak here but when you put the gun back together you get really bad FPS, trying switch out the air nozzle with a longer one. When I saw replace it with a longer one, I’m not talking about one that’s twice as long I’m talking about one that is microscopically longer such longer by .1mm - .2mm longer.
Lets say your stock air nozzle is 21.12mm long.



Try replacing it with a 21.22mm air nozzle.


Here are some other places to check for compression.

[Nightshade]

THAT was a bleeding AWESOME response. I applaud you, sir.

[MikeRarrmeh [64oz]]

yeah, exactly perfect

[SLINKEY]

this is how i do it.. pretty simple..

toss some high viscosity grease around the brass tube, slide the nozzle on, twisting it on. or get one with an O-ring inside.
i push the piston in like there saying, Then i also get the gear box to half cycle, and push the air nozzle out.
With no bb's in it, I blow into the end of the inner barrel.. it should be airtight if u got good compression, if u can blow air in there, take it back apart and redo it, Untill u cant blow air into it..

[Black Fox]

Nec

Excellent example!

With your permission. I would like to add this info to my original post.

Black Fox's Tricks of the Trade - Air Tight AEG
http://www.airsoftpacific.com/viewtopic.php?t=30907

This thread is already a sticky and your example would be an excellent addition to the information posted here.