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107 Posts
Discussion Starter · #1 ·
So i have a problem. I bought the PDI cylinder with cylinder head and PDI vacuum piston which were fine when i installed them. About 1 moth later i decide to open my cylinder cause there was horrible power loss. So i opened it and there was the o-ring which were glued to the piston were loose and destroyed to Little rubber bits. Same happened to the o-ring which were on the cylinder. I do not mean the O-rings which seals the gab between cylinder and the piston, and cylinder and cylinder head. Those o-ring were fine. So the power loss was fault of the "broken" vacuum valve. So i glued the valve hole with epoxy and the power of the rifle went up again. I also glued new O-ring to places of the old O-rings with epoxy. So few months later opened the cylinder again and the O-ring were loose again and grind-ed to small rubber bits.

Anyone have the same problem? I know the PDI vacuum piston is a piece of sh*t, but in here Finland other than pdi aps2 parts have become extremely hard to find. I have played without the O-rings like 1 year now, there is no problem with the power and the piston is not damaged (it may look like it, but the "shrapnel" is not aluminum, its the old epoxy). The problem is the sound. Huge "clang" sound comes when i fire the rifle. Imagine aluminum vs aluminum, not a silent sound.

So i decide today to fix this problem so here is my plan.

Picture 1:
The cylinder head in its original shape. The red dots represent the O-ring witch broke loose. Blue is the O-ring which seals the gab between cylinder head and cylinder
Picture 2:
The modified version of the cylinder head. Green is the epoxy and the red/purple/violet is rubber "mat"
Picture 3:
The cylinder head and piston head in impact. So the red dots are O-rings. And the piston head with the hole in the center is the valve thing.
Picture 4:
The modified cylinder head and modified piston head. Red/purple/violet is rubber "mat" and the green is epoxy
Picture 5:
The piston head in its original shape. Red is the O-ring witch broke loose and the blue is the O-ring which seals the gab between cylinder and piston. The "hole" in the center is the valve thing.
Picture 6:
The modified piston head. Green is the epoxy. Purple/red/violet is the rubber mat.

So will grind the last bits of old epoxy and O-ring rubber of with some sand paper and then i will wash the piston head and cylinder head with some turpentine to Wash Any lubrication oil off. Then i gently grind new glue base and glue the piston heads old O-ring gap with epoxy and glue some rubber mat to it. Same goes to the Piston head. The epoxy makes larger field to the piston to impact on and also works as the base of the rubber mat. The rubber mat makes the piston head cylinder head impact more silent.

So here is some questions:
-Has anybody else have the same Cinda of problem with the PDI vacuum piston?
-What do you guys think about my plan?
-Any suggestions how to improve my plan (buying a new piston/cylinder is not a option)

· Registered
107 Posts
Discussion Starter · #2 ·
Mission failed. The epoxy worked fine, but the rubber didn't attach to the epoxy and fell off. Also the rubber was to soft and the aluminum cylinder head would probably go trough it after 300 shots. So any suggestions what material should i use next? Harder rubber or something other material?
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