Author Topic: O-ring post from SSW (Read 687 times)

RandySmith · « **on:** June 14, 2014, 03:09:36 PM »

This is info that can be of benefit to anyone using IC engines, so I copied my post to this forum also.

#11. "RE: PA 75/65/61 Venturie O-rings"
In response to Reply # 10
Sat Jun-14-14 04:05 PM by Randy Smith

Good post for ANY engines . So some may not think, as the title suggest, only PA engines have this.
PA engines really have no place in the title about leaking old hard O-rings, they are not PA Engine products, and they are made by O-Ring mfg. companies.
ALL IC engines do exactly the same thing to O-rings, whether it is Sup Tiger, OS Max, and ENYA Magnum etc... O-Rings will get hard and deteriorate after several years of use; this has been going on for as long as they used O-Rings to seal carbs and venturies.
The black Nit rile O-Rings used in most all model engines are in fact very good sealing products, but as Dave has found, need to be replaced every few years, or in some cases every 10 years.
Normally the O-rings swell after exposure to heat and fuel/oil, taking care of the sealing even better, I find it is only when they start to get hard, that the problems arise.
If you want an alternative that can sometime do a better job of lasting, I recommend you try one of the silicone red O-rings, they last a long time, but are more delicate, as they will chip, or break easier. just be careful with them, those are the only 2 types I use, as I do not like the Viton O-rings for sealing, they do not do as good a job as the other 2. But try what you will, never hurts to test things.

Regards
Randy

Brett Buck · « **Reply #1 on:** June 14, 2014, 04:11:04 PM »

Quote from: RandySmith on June 14, 2014, 03:09:36 PM

Good post for ANY engines . So some may not think, as the title suggest, only PA engines have this.
PA engines really have no place in the title about leaking old hard O-rings, they are not PA Engine products, and they are made by O-Ring mfg. companies.
ALL IC engines do exactly the same thing to O-rings, whether it is Sup Tiger, OS Max, and ENYA Magnum etc... O-Rings will get hard and deteriorate after several years of use; this has been going on for as long as they used O-Rings to seal carbs and venturies.

The exception is the RO-Jett, where the O-ring is inside the barrel of the venturi boss. Not being exposed to air or light, they seem to last forever.

On the compression-type o-rings, it's quite critical to have exactly the right diameter cross-section. The compression of the ring is controlled by that, and if it is slightly too large, it can be compressed enough to fit, but then later "squirt" away from the flange. For a while there were some red o-rings with just a hair too much diameter, and you could get them to work for a while, but then they would move with disastrous results.

The other potential problem is that on the PA, ST, and similar arrangements, the compression of the o-ring also causes the venturi to tilt in the bore of the flange. The degree depends on how much tension there is, and how well the venturis fit the bore. They aren't all the same, and they aren't all round, at least after they have been run for a while. Tilting can cause two problems - it can leak air around the o-ring in the front, or it can leak fuel from the spray-bar pass-through down into the engine on the back side of the venturi bore. We check venturis for fit and select them for the least tilt.

Again, this cannot happen on the RO-Jett, there is no off-center compression since it's not held by tension, it goes down in a bore and it compressed symmetrically. This is offset by the fact that the venturi boss is short (meaning less sealing area under the spraybar) and that there is a sharp chamfer where you push the venturi in, which can cause the o-ring to be nicked when you push it in.

Brett

RandySmith · « **Reply #2 on:** June 14, 2014, 09:46:51 PM »

I have used O-rings in the Bore of many PAs, as I also have done some of those for David and many others, he did not want any past several years, I did offer.
I have also used in bore O-rings for about 30 to 35 years now in many many ST, OS, Magnum, Royal, Como, T Tiger and others, most all my modded engines use them too. I made KAZ a set of in plane adjustable dual O ring seal ventuires for his ST 60, as I have for other motors, so the Jett is not unique as that has been done on many many motors over the decades. The O ring seals on ST , OS, PA etc engines just have not been any sort of big problem.
You do know you can mess up in bore O rings too... easier than ST style. That is Just a differant ways to do things, still has a pressure seal, side pressure instead of top/bottom pressure, both are workable and do a good job

Randy

Author Topic: O-ring post from SSW (Read 687 times)

RandySmith

O-ring post from SSW

Brett Buck

Re: O-ring post from SSW

RandySmith

Re: O-ring post from SSW