O-ring Material?

I do a lot of carb restoration and while I prefer to use Viton O-rings where possible it's just not possible to find Viton for a lot of the various needed sizes therefor Buna N is the only choice.

In doing research on different materials it seems the main concern with Buna N is when the temperatures get above 250F. Don't think carbs should get that hot though, or at least not often.

I've spent a good bit of time on theGSresources.com and the guy that runs cycleorings.com is a member that sells a LOT of kits (all Buna N) and there has never one time been a complaint.

What do you think?

I've read quite a few sites long ago that explained why Buna N was as good, if not better, for Orings on carbs. So when it comes to Viton versus Nitrile (Buna N) I go with either one. Nitrile is cheaper, but sometimes you have to buy large quantities.

I have had some soaking in gasoline/ethanol for 3 years now, and the last time I checked, about a year ago, they were almost the same size and shape as new ones.

loudhvx wrote: I have had some soaking in gasoline/ethanol for 3 years now, and the last time I checked, about a year ago, they were almost the same size and shape as new ones.

Have you tried removing some from the gasoline and let them dry out for a few days? See if they are still pliable.

The large O-ring sealing the fuel pump to the tank on my son's car swelled up significantly, noticed when trying to reinstall a new pump. I was a bit panicked by this because the car was needed the next day so I took the O-ring and put it in an oven set to 170F for 45 mins and the O-ring shrunk back down to size. I'm guessing it was a Buna N O-ring.

Nessism wrote: In doing research on different materials it seems the main concern with Buna N is when the temperatures get above 250F. Don't think carbs should get that hot though, or at least not often.

I don't think temperature would be an issue with the carbs at all. The carbs are isolated from the head since they attach with a rubber boot. Also, carburetors tend to be colder than the atmosphere around them unless heated by the engine - this is due to the drop in pressure after the carb venturi, and the vaporisation of the fuel in the carb, both have a refrigeration effect. That's why carb icing can be an issue in high humidity/low temperature areas.

Also, if the carbs get to 250F you'll have more trouble than damaged o-rings - petrol starts boiling around 200F.

loudhvx wrote: I've read quite a few sites long ago that explained why Buna N was as good, if not better, for Orings on carbs. So when it comes to Viton versus Nitrile (Buna N) I go with either one. Nitrile is cheaper, but sometimes you have to buy large quantities.

I have had some soaking in gasoline/ethanol for 3 years now, and the last time I checked, about a year ago, they were almost the same size and shape as new ones.

When I check them, I take them out and let them dry for several hours.