Modify parts compression help

My modify set just arrived, the set included: a piston, a piston head, a cylinder, a cylinder head, and an air nozzle.

I tested the compression, and it’s really not that good (although this is the first time I have tested compression, so I don't have much to compare to), so I tested the compression of my stock vfc cylinder/cylinder head with the new piston head, and it has much better compression yet only having a singly o-ring plastic cylinder head. So my question is, is there something that I have forgotten to do to the new cylinder, or is this just a bad cylinder (I’ve heard that modify is not that bad of a brand), or have I heard wrong and it is a bad brand?

The cylinder is also different one than in the picture.
The set I got is: http://www.airsoftparts.ca/store2/index.php?main_page=product_info&cPath=66_126&products_id=1102


The black one is the modify. (I did not test compression with the cylinder heads like that :) )
http://imgur.com/S8kon7D

This is the set, the words markered out are “brass” and “stainless”
http://imgur.com/6ipUx3v

[Pinoy]

I can vouch Modify is a good brand. For 2-3 yrs my M4's has Modify gearboxes and 80% of internals are also Modify.

How did you test compression?

ok good to know.

I tested it by putting it together and blowing air in to the cylinder, and I also did a second test where I plugged the part the air nozzle goes on and then tried to compress the piston. The tests might not be very good, but the stock vfc cylinder was actually hard to compress, where as the modify one offered little resistance.

[Pinoy]

try compressing the piston without the air nozzle. if there is a good resistance then your piston o-ring and is good and cylinder head has good seal. then test again with the air nozzle installed. there should be a slight loss of compression but if little resistance means you have lots of air leak in the air nozzle. All Modify air nozzle I've bought has o-ring, check yours if has one.

also check the amount of lube in the cylinder and around the piston o-ring. too much lube is not good. new o-ring needs to be strecthed out a bit. i normally put the o-ring around the cylinder for about 30 minutes. if I am in a hurry to install it, i warm it up with a lighter . I've done these methods on o-rings and I've never damaged it and with great results lol.

otherwise, could be a lemon part. factory defect, out of spec? good luck!

ya, I tested the compression without the air nozzle.

I’ll try your stretch method, I think I’ll refrain from using fire as I don’t have a lighter, so the next best thing is my blow torch, which rarely ends well :-P

I may have put a tad too much oil in too, so ill clean it and try again with the stretched o-ring in the morning.

Thanks for all the help.

[Tjfast]

Something I noticed (could just be me ) But when I was testing compression, If I would move the piston slowly through the cylinder, it was appear to have minimal compression, but when I would test it moving piston pretty fast, it illustrated a much tighter compression.

Just an idea, hope it helps.

[Pinoy]

Something I noticed (could just be me ) But when I was testing compression, If I would move the piston slowly through the cylinder, it was appear to have minimal compression, but when I would test it moving piston pretty fast, it illustrated a much tighter compression.

Just an idea, hope it helps.

true. you will get better compression on an actual operation because the o-ring stretches/expands when the piston moves faster

there is reallty nothing more to add. Pinoy hit the nail right on the head.....

i just wanted to say hi...... HI

i tested it again with the stretched oring and less oil, and it had good compression!
thanks for the help guys, the combo of the two must have done it.

now it's time to buy some grease and some new bushing, and then i'll have a working aeg again

P.S. Hi Gunny