Technical What's with 'O' rings?

Ok, I have been finding out that the 'O' rings I'm using to seal my Model T fuel tank cap keep growing. I ***ume it's the contact with the new ****ty fuel we are stuck with and I am not even tightening the cap very much because that seems to make the 'O' ring bind. Are there special O rings that are not affected by fuel or am I just gonna have to live with it and replace em often?

 

make a "paper" gasket and throw the o-ring away

 

Or try Viton O rings.

 

Hum paper, never thought of that? I could give that a try. Thanks. What makes Viton O rings hold up better than hardware ones? Special rubber?

 

there are at least a dozen different kinds of "rubber" that O rings are made of. Viton would indeed be good for what you're trying to do. McMaster Carr (a**** others) sells quite a variety of O rings, all different materials, all different sizes. Usually it costs about $10 for a bag, the smaller they are, the more you get in a bag.

 

Hardware store o rings are for plumbers, not hot rods.

Get a quality viton o ring.

 

didn't you hear? everything ****s now and it will only be getting worse.

I'd use cork gasket material before paper.

 

I just went to the Vinton web site and now realize O rings are nit created equal. Thanks for enlightening me Dumprat!

 

These cats have whatever you need.
http://www.oringsandmore.com/

 

Chinese rubber.

 

Different types of rubber compounds for different types of chemicals

 

try a place that makes up hyd. hoses, they usually have different types of o rings and even sheets of rubber that are fuel resistant. you can make a gasket for your cap similar to what the old "Gerry Cans" used instead of o rings if you want.

 

Never buy o-rings at Harbor Freight if you actually want them to "seal" something. They will do exactly what you're experiencing.

 

What you need is a Nitrile (Buna-N) rubber O ring. Here are a couple of sources.
http://www.rubberstore.com/catalog/nitrile-orings-c-33_39.html
http://www.marcorubber.com/buna.htm

 

Fail

 

what year did model T start using o-rings?

 

get a viton one , they make them in flat o rings which would suit this purpose better ( made for 55 gallon drums ) and drip some gas on it before you twist the cap on to lube it so it won't stick .

 

Actually Buna-n is a poor choice for contact with todays automotive gasoline. If you look deeper into the compatibility, fuel oils/diesel is ok but most companies suggest it not be used with gasoline. Viton is a no brainer.

 

Never. Ford build over 15 MILLION T's and none of them left the factory with any seal under the gas cap. Maybe the repop cap is the problem. Be sure the tank and cap surface is smooth, you'll have more thread contact without that o ring. Bob

 

I think your problem is using a barrel bung for a gas fill. Those are made with a sealing surface made for a flat rubber seal or tapered pipe threads that need to be tightened with a bung wrench, not just hand tight. It's a little late to replace it now but if you ever need to repaint the tank weld on a section of filler neck with a nice round gas cap.

 

Gas Cap Gasket

Item Number: 2901G
Per Car: 1
Year: 1909-1927
Condition: New
Price: $0.40 each

 

A thorough thrashing out of O-rings would make a GREAT tech article if anyone here knows that stuff...which is pretty much certain.
Sizing specs, how to measure diameters and cross sections, types of material...I'm about to hunt for new ones for a WWII filter, and real knowledge would be great.

 

Nope. That is a stock, early style, recessed Model T gas cap not a barrel bung

 

you may have a 70 durometer o-ring and may be needing a 90 durometer instead. boss fitting o-rings are 90 durometer too. same size your using just tougher. tell me (pm) what size we may have some. best of luck to you.

 

A winged "Speedster" Model T cap may allow more force to be placed on it, and might look better. Check with Don Lang's website for price, he is a HAMB member. Bob

 

It looks to me like your o-ring is not confined on the outside diameter. That's why it's extruding out when you squeeze it down. O-rings need to be captured on both the inside and outside to work properly. I think you would have better luck sealing with a flat ring rather than an o-ring. Bill

 

Thanks for all the opinions. I think the solution lies somewhere in the "composition" of the rubber used. I now know there are 'O' rings that are suitable to be used near gas and other fuels and ones that are not.

 

Have you checked to see both surfaces are FLAT? Cant't understand how it worked fine on stock T's, with no gasket, but you are having problems. Bob

 

Bob, the tank is a repro from on of our Alliance members and I have no idea why the O ring keeps stretching other than it fits tight when new and after exposed to gasoline it loses its shape. Im just gonna deal with it for not until I can get around to an O ring that is designed to be used in this environment.

 

Yep not all O rings are created equal. Find the proper O-ring, Viton has been suggested, for the job.