Author Topic: California gasoline additive resistant o-rings  (Read 505 times)

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Offline LeeM

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California gasoline additive resistant o-rings
« on: August 02, 2017, 05:39:55 am »
On my 2000 Connie the vacuum petcock started leaking. I am pretty sure the inner piston o-ring is swollen as the valve just barely closed during a workbench test. And further, I didn't know how the diaphragm part works because I couldn't pull the piston out. I can't quite figure out how it works and I am waiting for a Murph's rebuild kit before pulling the diaphragm apart.

Here is the evidence: I drained the motorcycle's last full tank of Shell premium and used some of the gasoline to refill my 10 HP vegetation shredder. I'm piddling away my summer vacation motorcycle fun time working on the yard. The shredder is about a 20  year old OHV Briggs and Stratton engine. After filling the tank with motorcycle gasoline, the shredder ran about 30 minutes and stopped just like it had run out of gas. The gas tank was still full. Checked the oil, it is OK and still clean from last year's maintenance. I waited about 20 hours and the shredder restarted just like usual on the second pull of the starter rope. The engine ran for 30 seconds and died with the running out of gas blubbety blub sound. No I waited 4 mores hours. This time the engine started and ran for 5 minutes at full speed.

What I think is going on is the neoprene needle valves and o-rings are swelling up when the fuel blend changes. After one or two days the swelling goes down. A year ago I had my Connie towed home ($100) after putting in a full tank of my local convenience store gasoline that I knew was fresh from the delivery truck a few days earlier.

I googled for "fuel resistant o-rings" to see what has changed in the 40 years since I helped design and build fluid filling machinery. The two main o-ring materials are still Buna-N and Viton. Both of them have a  warning flag for Ketones(MEK). Teflon o-rings are available but they can't be stretched like usual o-rings.

I am going to see if I can learn the timetable for the seasonal blend changes, and find out the names of the chemicals being added or subtracted from the gasoline.

Next, does any reader know any simple test to reveal when the gasoline blend is changed?

Any chemist out therre? What is actually going on with methyl ethyl keytone and the generic neoprene rubber that was used in carburetors 20 years ago? I have observed the rubber swelling is transient. What is going on with MEK molecules and the neoprene rubber? Why is the swelling transient or how come I am seeing a problem that goes away in 24 to 48 hours?

Offline RWulf

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Re: California gasoline additive resistant o-rings
« Reply #1 on: August 02, 2017, 01:04:54 pm »
I may be wrong but didn't California ban MEK.
Wasn't that the stuff that was showing up in your drinking water ?

Offline Steve in Sunny Fla

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Re: California gasoline additive resistant o-rings
« Reply #2 on: August 05, 2017, 01:12:10 am »
I don't know about the additives, but ethanol will swell buna by up to 40%. The fuel needle tips need to be viton. Steve
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Offline VTconnie

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Re: California gasoline additive resistant o-rings
« Reply #3 on: August 05, 2017, 01:20:53 am »
All I know is thank god I can fill up with E-0..
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Offline Stasch

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Re: California gasoline additive resistant o-rings
« Reply #4 on: August 05, 2017, 11:04:42 am »
All I know is thank god I can fill up with E-0..

All I can think of is Napolean Dynamite saying:  "Lucky"
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Offline JDM

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Re: California gasoline additive resistant o-rings
« Reply #5 on: August 05, 2017, 11:18:14 am »
I don't know about the additives, but ethanol will swell buna by up to 40%. The fuel needle tips need to be viton. Steve

Steve, when you rebuild the C-10 carbs do you use Viton? I bet the answer is yes.

Offline WillyP

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Re: California gasoline additive resistant o-rings
« Reply #6 on: August 05, 2017, 09:41:16 pm »
Sounds like your shredder might have some other issue... maybe tank venting, a coil or ignition module heating... I can't imagine how a rubber carb part would swell, shut off fuel, then un-swell in four hours while still in the same fuel that caused the swelling in the first place.
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