Hi Guys, is it possible for a needle valve O-ring to swell up and make the needle valve really hard to turn? I have an OS 55AX and an OS 70 Surpass and after sitting a while both of them have really stiff turning needle valves. I pulled the needle valve out, the O-ring shows no damage, the threads are clean and look good, and put the needle valve back in with plenty of my after run on everything. For after run oil I use a mixture of ATF and Marvel air tool oil. Before putting the engines away for the winter last year, I squirted lots of after run oil in the carb and fuel intake nipple on the carb area. Is it even remotely possible that my after run oil is causing the O-ring to swell up, making the needle very stiff to turn?

Thanks loads,

Ernie Misner

Yes. OS uses silicone O-rings on many needles. Petroleum products will cause them to swell.

Not getting too many replies here..... I guess both of my ARO components are petroleum products huh? (ATF and air tool oil) So what can a guy inject into the carb and needle valve area if storing an OS engine?????? ... that won't cause the O-ring to swell up?

Thanks,

Ernie

i guess that explains it then....lol those hard to turn needle valves scare me when tuning......

For after run oil, I used to use performance specialties after run oil. about 8oz. for 8 bucks. The last couple years i started running Mobil 1 0w30 for after run oil. Been happy with it and it's about 8 bucks a quart

When I worked at a power sports dealer (motorcycle) I raided the carburetor o-ring assortment. Found what I needed and they are nitro and petroleum resistant.

Ken

I know it doesn't answer your question, but I have an OS 70 that I bought used off RCU.  The needle valve has since become very stiff to turn and I have also used ATF as an afterrun.  It concerned me at first, but I didn't notice any negative effects.

Folks, why not do away with the o-ring. simply use a piece of large fuel tubing between the valve and body. Seals great and does away with the rachet. I have used this method and it works good. Good luck, red

I run diesel conversions of glow engines. The fuel causes the o-rings to swell. Sometimes they get pretty tight, but it doesn't seem to be a big issue. I think, but can't be sure, that if you remove the oil from the o-ring it will eventually shrink back down. I understand certain synthetic ATF or motor oils will not swell silicone o-rings.

Hi!
The reason the needle gets stiff isn't from the O-ring expanding ...it's from to little oil on the O-ring!
Just loosen the needle and put whatever oil you wamt on and everything will be just fine!

Had same problem on a OS.25FX, yes the O-ring is swelling, ordered replacements thru Tower and everything is good to go now. Believe OS is getting poor quality O-rings from a Chinese supplier.[>:]
Have several OS engines for many years and never had a problem with O-rings before.

No Jaka, lots of oil was put in the needle and threads before storing and that is the problem, it swelled the O-ring way up. I even pulled the needle back out, tons of oil in there, and added even more. Tight, tight, tight O-ring. In the OS manuals it used to say not to put petroleum products (ARO) down the carb and this must be why. Actually just putting it through the carb probably isn't a problem, but I drenched the needle and O-ring with it and let it sit all winter that way thinking I was doing it a favor....

Thanks for the great replies guys!

Ernie

On my OS 55AX, it swelled up so tight that I couldn't even turn it when the engine was running..... vibration and all. No fun!

Ernie