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Old 03-19-2012, 12:54 PM
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Jonezy Jonezy is offline
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Location: Perrysburg, OH
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For the compression test, did you test it with the nozzle retracted or forward? A common misconception about the compression test is that you have to have the air nozzle pushed back against the cylinder head in order to test it. This is not true. The air nozzle needs to be able to seal when in the forward position as this is where it will be whenever the piston begins its stroke. Let's go through your parts list and address a few things:

Bravo double seal cylinder head: Check for leaks around where it seals in the cylinder. If you find a leak, use a bead of silicone sealant around the first o-ring (i.e. the one that sits furthest from the air nozzle), reassemble, and let cure.

ICS polycarb orange piston: Not my favorite choice in pistons but check for interference along the piston rails. With the entire cylinder assembly removed, the piston head and main spring removed, the piston itself sitting in the rails in the gearbox, and the gearbox screwed together, see if the piston can travel freely back and forth in the gearbox. If there is much friction from the rails binding in the shell, you may have to file the rails on the piston a little wider and/or deeper.

Bravo aluminum piston head with an x head o-ring: Ditch the x-ring and use a regular ol' o-ring. X-rings do nothing to help improve air seal. Take a regular piston head o-ring, stretch it around a cylinder, and heat it gently with either a heat gun or a torch. Be careful because it's easy to apply too much heat and make the o-ring snap. Wait for it to cool first before you remove it from the cylinder. If you did it correctly, you should now have the best sealing o-ring possible. Grease it minimally with some silicone grease after it's installed on the piston head and don't grease the inside of the cylinder as the nublets on YouTube will tell you. Let the grease you put on the o-ring coat the cylinder.

Modify type 0 cylinder: This should be fine, just check to see if the chrome plating is worn off on the inside. The piston head may have cut some lateral grooves into it.

JBU M140 spring: This should be fine, just make sure you orient the coils with the close-pitched end nearest to the spring guide.

Modify air seal nozzle: This is not so good. You can try to swap out the o-ring for an SHS one or one from McMaster (I have tons, PM me if you need some) to try to get it to seal right, but I've yet to see a cylinder head that they work properly with. You may want to swap that out for a Guarder, Dream Army, or GURU one if you can't change the o-ring out and get it to seal.

A&K hopup: If you're using the oddly-shaped A&K bucking without the molded lips, you should look into getting a regular one. I've found that those don't always seal properly against the air nozzle and they leak out the back like nothing I've ever seen before. The hopup chamber itself might not be tight enough to prevent air from escaping between the barrel and the bucking and out the back of the bucking, so after you've slid it in place on the barrel, peel the back edge (towards the muzzle) of it back and put a bead of silicone sealant between the barrel and bucking, then install it into the chamber to let it cure. It's like the "floss mod" but much better.

Let me know how this works for you.
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