Piston head O-rings

Whiskey · April 9th, 2010, 13:01

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 · April 9th, 2010, 13:14

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 · April 9th, 2010, 13:15

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

Janz99 · April 9th, 2010, 13:26

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 · April 9th, 2010, 13:53

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 · April 9th, 2010, 15:32

Quote:

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 · April 9th, 2010, 15:50

Quote:

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 · April 9th, 2010, 23:30

Viton's good.

ThunderCactus · November 24th, 2010, 01:09

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 · November 25th, 2010, 18:28

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 · November 25th, 2010, 18:45

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 · November 25th, 2010, 18:48

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 · November 25th, 2010, 18:50

Quote:

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 · November 25th, 2010, 20:29

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.

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April 9th, 2010, 13:01	#1
Whiskey formerly BLACKWATER204 Trader rating Join Date: Mar 2010 Location: Winnipeg	Piston head O-rings 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 . __________________ All right, they're on our left, they're on our right, they're in front of us, they're behind us... they can't get away this time! - Lieutenant General Lewis B."Chesty" Puller (when surrounded by 8 enemy divisions) Born to fight, trained to kill, ready to die, but never will.

April 9th, 2010, 13:53	#5
Amos Trader rating Join Date: Aug 2006 Location: Japan	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. __________________ Custom Builds: FA3674U Krinkov G3SD6

November 25th, 2010, 18:45	#11
Boyso a.k.a. LastSpartan Trader rating Join Date: Jul 2009 Location: Québec city	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. __________________ NEW BACON FOR SALE! "WHEN I DIE BURY ME UPSIDE DOWN SO THE WORLD CAN KISS MY ASS" -Platoon

April 9th, 2010, 13:14	#2
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	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).

April 9th, 2010, 13:15	#3
coach aka coachster Trader rating Join Date: Mar 2008 Location: T dot	I've been using the MASK piston heads and the orings ARS supplies with them are pretty good.

April 9th, 2010, 13:26	#4
Janz99 Trader rating Join Date: Apr 2009 Location: Winnipeg	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

April 9th, 2010, 23:30	#8
G26 Trader rating Join Date: Feb 2009 Location: South East Asia	Viton's good.

November 24th, 2010, 01:09	#9
ThunderCactus Not Eye Safe, Pretty Boy Maximus on the field take his picture! Trader rating Join Date: Feb 2007	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!

November 25th, 2010, 18:28	#10
xaMdaM Trader rating Join Date: Nov 2010 Location: Aurora, Ontario	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?

November 25th, 2010, 18:48	#12
Amos Trader rating Join Date: Aug 2006 Location: Japan	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. __________________ Custom Builds: FA3674U Krinkov G3SD6

November 25th, 2010, 20:29	#14
ThunderCactus Not Eye Safe, Pretty Boy Maximus on the field take his picture! Trader rating Join Date: Feb 2007	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.

Piston head O-rings

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