Piston heads and O-rings

Jimski · October 27th, 2008, 16:05

Heya all,

I just received two systema bore-up kits, and they both have an O-ring on the piston head that is rather loose in the cylinder - which makes me question about the air seal during the action.

According to your experience, how does the O-ring diameter influence the seal and FPS ?
Is it bad if a bigger O-ring risks slowing down piston action ?
Does it change a lot from a loose O-ring to a very tight one ?

and btw what are the standard dimensions for a ver3 piston O-ring ? for ordering online...

thanks.

Crunchmeister · October 27th, 2008, 16:25

The o-ring needs to be larger than the piston and rather loose. The vented piston heads are made exactly for that. As pressure in the cylinder increases, that pressure is directed through the holes on the piston head and out into the groove wher ethe o-ring sits, pressing it even tighter to the cylinder wall to maximize the seal and maintain pressure inside the cylinder. Properly lubing the cylinder interior is enough to prevent any slowdown of the piston cycling.

Jimski · October 27th, 2008, 16:32

ok thanks.
So I guess it means you cannot really achieve proper compression just by moving the piston manually, right?

Crunchmeister · October 27th, 2008, 16:36

Actually, for testing purposes, you can actuate the piston manually to test compression. I do it all the time when reassembling a mechbox. Before installing the spring, I pull the piston back, plug the nozzle with my finger, and press the piston in. If all is well, it should provide good compression.

Jimski · October 27th, 2008, 16:39

that's what I do but I wasn't sure..the sloppy O-ring makes it difficult to diagnose.
anyway thanks!

Kos-Mos · October 27th, 2008, 19:10

It is normal apparently.

All the bore-up kits I found had issues with the size of the o-ring.

You can fix this quite easilly but letting the o-ring stand in some light silicon oil (around 10wt is fine) for about 2 days. The o-ring will expand a little, usually enought to fix the gap. And it makes the o-ring "oilly".

ILLusion · October 27th, 2008, 20:37

It is normal installation procedure for the bore-up kits to stretch the o-ring out a bit first.

This is done by pulling one end of it out of the piston head gap and just "rolling" it over the face of the piston head. Do this around the full circumference and it should be done in about 10 seconds.

Systema training indicates this as standard practice.

TriChrome · October 27th, 2008, 23:48

You can stretch the o-ring like Illusion mentioned, but the properties of o-ring rubber is that it goes back to it's own shape in time (unless you stretch it enough to make tiny rips in it).

A better method is to add heat to the mix which will permanently stretch the o-ring a little better. Put the o-ring over the cylinder, and put a lighter under it (about an inch away). GENTLY heat the o-ring as you rotate the cylinder. I usually do about 10 seconds, then let it cool down and repeat a couple times. Let it completely cool on the cylinder and re-install it.

ILLusion · October 28th, 2008, 02:18

Through use, the surge ports on the face of the piston head will force the o-ring open to seal with the cylinder.

Repeated use of the gun will keep it expanded for proper use. If the gun's been sitting for a while, a couple of rounds through it will help get the expansion back up.

Jimski · October 28th, 2008, 11:00

thanks a lot guys, very useful info !

yesterday night I got 383 fps out of the bore-up kit just by adding grease around the o-ring and a lot in the nozzle.
However I suspect the fps could go down as grease gets blown away through time, today I will try your recommandations.

m102404 · October 28th, 2008, 11:09

With any "new in package" piston heads, I remove the o-ring completely and give it an inspection and "work-out" before testing compression. If it's marginal (most times it's ok), I'll give it a stretch/heat-treatment as TriChrome describes.

You should definitely be able to test for compression manually. With the cylinder nozzle plugged (just finger pressure will do), a sharp push of the piston is all you need. Ideally, the piston should lock up immediately (once past any ports in the cylinder). If it's a slow leak, take a close look at the o-ring, the rim of the piston head (sometimes there's mold deformations which hang up the o-ring), and the surface of the cylinder (it should be smooth to the touch everywhere).

O-rings are cheap and easy to get at hardware stores. Some of them fit tighter with some piston heads and some looser with others.

Best of luck,

Tys

Home	Forums	Register	Gallery	FAQ	Calendar
Retailers	Community	News/Info	International Retailers	IRC	Today's Posts

British Columbia	Alberta
BCAC	EAR
Op-For	JOC
Northern Arms Airsoft	Skunkworx Airsoft
Airsoft Kelowna	RAAT
Prince George Airsoft	Manitoba
Saskatchewan	MAA
SK Airsoft	Ontario
PDW	Airsoft Ottawa
South Sask Mercs	Snow Dragons
Quebec	1st Ranger Platoon
PQAC	Wolfpack Tactical
1st Pathfinders Regiment	TTAC3
Quebec Airsoft
MTX Airsoft	Atlantic
FAQc	Atlantic Airsoft

October 27th, 2008, 16:05	#1
Jimski Trader rating Join Date: Jun 2005 Location: Montreal	Piston heads and O-rings Heya all, I just received two systema bore-up kits, and they both have an O-ring on the piston head that is rather loose in the cylinder - which makes me question about the air seal during the action. According to your experience, how does the O-ring diameter influence the seal and FPS ? Is it bad if a bigger O-ring risks slowing down piston action ? Does it change a lot from a loose O-ring to a very tight one ? and btw what are the standard dimensions for a ver3 piston O-ring ? for ordering online... thanks. __________________ Last edited by Jimski; October 27th, 2008 at 16:09..

October 27th, 2008, 16:25	#2
Crunchmeister Trader rating Join Date: Nov 2007 Location: In your bedroom going though your underwear drawer	The o-ring needs to be larger than the piston and rather loose. The vented piston heads are made exactly for that. As pressure in the cylinder increases, that pressure is directed through the holes on the piston head and out into the groove wher ethe o-ring sits, pressing it even tighter to the cylinder wall to maximize the seal and maintain pressure inside the cylinder. Properly lubing the cylinder interior is enough to prevent any slowdown of the piston cycling. __________________

October 27th, 2008, 16:32	#3
Jimski Trader rating Join Date: Jun 2005 Location: Montreal	ok thanks. So I guess it means you cannot really achieve proper compression just by moving the piston manually, right? __________________

October 27th, 2008, 16:36	#4
Crunchmeister Trader rating Join Date: Nov 2007 Location: In your bedroom going though your underwear drawer	Actually, for testing purposes, you can actuate the piston manually to test compression. I do it all the time when reassembling a mechbox. Before installing the spring, I pull the piston back, plug the nozzle with my finger, and press the piston in. If all is well, it should provide good compression. __________________

October 27th, 2008, 16:39	#5
Jimski Trader rating Join Date: Jun 2005 Location: Montreal	that's what I do but I wasn't sure..the sloppy O-ring makes it difficult to diagnose. anyway thanks! __________________

October 27th, 2008, 20:37	#7
ILLusion GBB Whisperer Trader rating Join Date: Jun 2002 Location: Toronto	It is normal installation procedure for the bore-up kits to stretch the o-ring out a bit first. This is done by pulling one end of it out of the piston head gap and just "rolling" it over the face of the piston head. Do this around the full circumference and it should be done in about 10 seconds. Systema training indicates this as standard practice.

October 27th, 2008, 23:48	#8
TriChrome Trader rating Join Date: Aug 2008 Location: New Jersey, USA	You can stretch the o-ring like Illusion mentioned, but the properties of o-ring rubber is that it goes back to it's own shape in time (unless you stretch it enough to make tiny rips in it). A better method is to add heat to the mix which will permanently stretch the o-ring a little better. Put the o-ring over the cylinder, and put a lighter under it (about an inch away). GENTLY heat the o-ring as you rotate the cylinder. I usually do about 10 seconds, then let it cool down and repeat a couple times. Let it completely cool on the cylinder and re-install it.

October 28th, 2008, 02:18	#9
ILLusion GBB Whisperer Trader rating Join Date: Jun 2002 Location: Toronto	Through use, the surge ports on the face of the piston head will force the o-ring open to seal with the cylinder. Repeated use of the gun will keep it expanded for proper use. If the gun's been sitting for a while, a couple of rounds through it will help get the expansion back up.

October 28th, 2008, 11:00	#10
Jimski Trader rating Join Date: Jun 2005 Location: Montreal	thanks a lot guys, very useful info ! yesterday night I got 383 fps out of the bore-up kit just by adding grease around the o-ring and a lot in the nozzle. However I suspect the fps could go down as grease gets blown away through time, today I will try your recommandations. __________________ Last edited by Jimski; October 28th, 2008 at 11:03..

October 28th, 2008, 11:09	#11
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	With any "new in package" piston heads, I remove the o-ring completely and give it an inspection and "work-out" before testing compression. If it's marginal (most times it's ok), I'll give it a stretch/heat-treatment as TriChrome describes. You should definitely be able to test for compression manually. With the cylinder nozzle plugged (just finger pressure will do), a sharp push of the piston is all you need. Ideally, the piston should lock up immediately (once past any ports in the cylinder). If it's a slow leak, take a close look at the o-ring, the rim of the piston head (sometimes there's mold deformations which hang up the o-ring), and the surface of the cylinder (it should be smooth to the touch everywhere). O-rings are cheap and easy to get at hardware stores. Some of them fit tighter with some piston heads and some looser with others. Best of luck, Tys

Piston heads and O-rings

Upgrades & Modifications