Piston head O-rings

[Whiskey]

Well as a long time perfectionist with my aeg builds i find that the O-rings that usualy come with Cylinder kits/FTK's or just plain new piston heads are usualy crap and giving less than ideal compression. Im curious to know what people are doing about this and if they are- A: just using the O-ring that came with the kit reguardless if its actualy sealing or not. B: Sourcing out something else that will give better performance. I however have sided with option B and source out my own O-Ring's for all my personal builds. The O-ring's that i use are called a Viton seal O-ring and are usualy found in 250,000 PSI Hydrolic systems, needless to say there up to the task . I will Post up specs later for anyone who wants them .

[m102404]

Here's a quick "trick" to improve the piston head/cylinder airseal.

Take the O-ring off the piston head, clean it. Stretch it over the cylinder. Heat it evenly with a lighter/heat source. Hot enough so the rubber changes shape, not so hot that you melt any part of it. Let it cool completely while on the cylinder.

Take it off, clean the ring/cylinder, lightly relube the oring/cylinder, reinstall oring to the piston head.

Compression should be solid between the piston head/cylinder now.

Tys

*note: this will not fix an o-ring that fits the piston head very poorly (i.e. too thin/undersized).

[coach]

I've been using the MASK piston heads and the orings ARS supplies with them are pretty good.

[Janz99]

I have the same problem. The orings on both the pistons and piston heads never seal as well as they should. I have a huge asortment of vitan o-rings at work, and normaly find the one that fits and seals.

If you dont have access to orings, just take the whole assembly down to a hydraulic shop and find one that fits/seals properly. The hydraulic shoups normaly have a huge varity.

Ryan

[Amos]

The ones that come with the ARS MASK kits are FANTASTIC.

I'm regularly getting +/- of 3 FPS when using MASK piston heads in an AEG.

[Whiskey]

Originally Posted by Janz99

I have the same problem. The orings on both the pistons and piston heads never seal as well as they should. I have a huge asortment of vitan o-rings at work, and normaly find the one that fits and seals.

If you dont have access to orings, just take the whole assembly down to a hydraulic shop and find one that fits/seals properly. The hydraulic shoups normaly have a huge varity.

Ryan

LOL thanks janz for the O-rings YOU supply me ! (its Steck by the way)

[Whiskey]

Originally Posted by m102404

Here's a quick "trick" to improve the piston head/cylinder airseal.

Take the O-ring off the piston head, clean it. Stretch it over the cylinder. Heat it evenly with a lighter/heat source. Hot enough so the rubber changes shape, not so hot that you melt any part of it. Let it cool completely while on the cylinder.

Take it off, clean the ring/cylinder, lightly relube the oring/cylinder, reinstall oring to the piston head.

Compression should be solid between the piston head/cylinder now.

Tys

*note: this will not fix an o-ring that fits the piston head very poorly (i.e. too thin/undersized).

Interesting method, im going to give that a try some day.
Another method ive seen is to soak the O-ring in power steering fluid for a week or so and that should swell the O-ring a bit and possibly give a better seal.

[G26]

Viton's good.

[ThunderCactus]

Don't know if I'd wait a week, I've seem some swell 30% just overnight. But it's absolutely a viable method. You can't break what's already broken so there's no harm in trying it out atleast!

[xaMdaM]

How tight a seal do you guys expect from your Piston/Cylinder? Should it be "syringe" tight? Wouldn’t that offer too much friction?

Having worked on several AEG's now, I noticed that the seals were never 100%. I did test fit some better O'rings to check to see if I could tighten the fit, but I am positive that too-tight a fit will cause too much friction and backpressure that may reduce performance. My fluid dynamics education (years ago, but I am still an active engineer.. but not in my original field...) tells me that there needs to be a happy medium between too much friction and too much bypassing air. How tight a fit do you guys go for before performance degrades?

[Boyso]

You piston head is ported. When it moves forward, the o-ring expands tightening the seal. When it goes back, the o-ring retracts.

Using silicon oil of heavier weight on the cylinder walls and on the o-ring will reduce the friction.

But at the same time, my AEG with almost everything stock has poor airseal with the piston head/cylinder/cylinder head. Still, I'm getting 347 +/- 2.

[Amos]

don't use oil in the cylinder, it'll ooze out, dilute every other oil and cause a huge mess (normally ending up inside your motor)

Use a silicon GREASE inside the cylinder.

[Boyso]

Originally Posted by Amos

don't use oil in the cylinder, it'll ooze out, dilute every other oil and cause a huge mess (normally ending up inside your motor)

Use a silicon GREASE inside the cylinder.

Yeah that's what I meant :P

Sticky-G.

[ThunderCactus]

The piston to cylinder fit should be loose, there should be no resistance from the size of the o-ring. If there is, it may cause your piston to strip firing full auto since it can't return fast enough.
The best seal you can get is 99% with the air nozzle forward. Your piston head shouldn't actually leak AT ALL. Where you lose all your pressure is in the cylinder head - air nozzle and air nozzle - hop rubber connections
Test for compression while having either your finger over the cylinder head's nozzle, or have the air nozzle pushed all the way back with your finger over it and check for seal.
Then do the same but install the spring on the tappet plate so the air nozzle is forward.

I've sized up all my o-rings and made myself a custom air nozzle to get 99% seal between air nozzle and cylinder head.
You can do it with stock parts, the ARS cylinder heads are slightly oversize on the nozzle end so they seal really well, but the air nozzle is the hardest thing to get right.