Over the years, we've been asked if our carb kits o-rings are made of Viton®, Dupont’s registered trademark for their fluorocarbon (FKM). The answer is no because we simply are not convinced of the need to use this expensive material and pass the costs on to our customers.
While both Nitrile (Buna-N) and Viton® are in the class of elastomers, there is a recent trend towards using Viton® in the automotive industry due to its alleged superiority to Nitrile relating to heat tolerance, compression, permeation, as well as its defense against biofuels particularly ethanol.
Unfortunately, we find contradicting data on the comparisons of Nitile and Viton® ethanol compatibility leading us to believe the promotion of Viton® superiority is marketing propaganda. Does anyone remember the R12 refrigerant (Freon®) scare when R134A came on the market? Owners of pre-1994 cars were scared into converting their R12 systems to handle the new ozone safe R134A Freon to avoid corrosion of their rubber and plastic components. History proved the scare was unfounded.
Similarly, what of the scare about the effects of Nitrile exposure to ethanol, which is nothing more than grain or ethyl alcohol? Besides being intoxicating alcohol that dates back centuries, ethanol has a long history of being the fuel for heat and light. Its use in automotive combustion engines is nothing new. The original 1908 Model T Ford could be modified to run on either gasoline or ethanol because Henry Ford was a supporter of homegrown renewable fuels.
- Ethanol was used to fuel cars well into the 1920s and 1930s as several efforts were made to sustain a U.S. ethanol program. Standard Oil marketed a 25-percent ethanol by volume gasoline in the 1920s in the Baltimore area. Ford and others continued to promote the use of ethanol, and by 1938 an alcohol plant in Atchison, Kansas, was producing 18 million gallons of ethanol a year, supplying more than 2,000 service stations in the Midwest. By the 1940s, however, efforts to sustain the U.S. ethanol program had failed. After World War II, there was little interest in the use of agricultural crops to produce liquid fuels. Fuels from petroleum and natural gas became available in large quantities at low cost, eliminating the economic incentives for production of liquid fuels from crops. Federal officials quickly lost interest in alcohol fuel production, and many of the wartime distilleries were dismantled. Others were converted to beverage alcohol plants. “Outlook for Biomass Ethanol Production and Demand” (PDF) by Joseph DiPardo. United States Department of Energy
Ethanol used over a century ago apparently posed no particular problem to the early engines that used Nitrile gaskets and o-rings. Otherwise, there would’ve been a wide search for a better replacement material. The gasoline sold in our area has 10% ethanol. We placed Nitrile o-rings in 40% ethanol and have seen no measurable difference in the o-ring over a week’s time.
What about the need for increased heat tolerance in carburetor o-rings? The fuel of a spark-ignition engine is mixed with air within its flammable limits and heated above its flash point before ignition by the spark plug. A chemical’s flash point is the lowest temperature where fluid evaporates to form a combustible concentration of gas. The flash point of ethanol or ethyl alcohol is 55-63 F and gasoline or petrol is –45 F. Nitrile’s temperature ranges as low as -70 F and up to 275 F. Viton®’s range is to –40 F to 450 F. We found data that stated 75 Duro Viton® only ranges down to –15 F which is far from gasoline’s flashpoint of –45F.
If higher heat tolerance is due to concern about the effects of engine overheating, safeguarding your carburetor o-rings should be the least of your worries. How about a cracked or blown head gasket, allowing seepage of coolant into the cylinders and warping the heads? A burst radiator and hoses? A burned piston or engine seizure? And worst of all, your engine catching fire if a carburetor happens to be flooded at that time.
Should your engine ever catch fire, keep in mind that Viton® puts off hydrogen fluoride gas when it burns which turns into hydrofluoric acid (HF) in the presence of water. Breathing in hydrogen fluoride can cause severe lung damage. When approaching a toasted engine, always use adequate protection against handling HF because of the possibility of Viton® being used in other automotive engine gaskets and seals.
Elastomer compression set is the measurement of how fast it returns to its original shape when compression is removed. 100% compression is bad. The lower the number, the less likely the elastomer will “set” and lose sealing pressure under compression. The compression set of fluorocarbons (Viton®) is 11%, which is greater than Nitrile at 4% but both are considered to be in the very low range when you compare against 100%.
Permeation is the rate a gas or liquid can be transmitted through the elastomer. Nitrile has a rating of 8 while fluorocarbon is rated 12.7, which is not a significant difference and not of any consequence by the use of either material.
Viton® is an excellent product in situations requiring resistance to a broader range of chemicals that apparently are not found in every day gasoline (petrol). Higher heat tolerances are necessary in turbine and jet engines but not the liquid-cooled combustion engine of the Gold Wing. Customers who bought our carb kits over the past decade know this is a non-issue.
How do you know you truly have Viton® o-rings instead of Nitrile? Both Viton® and Nitrile have a poor resistance to esters, ethers, ketones, amines and brake fluid. Viton® excels in its resistance to halogenated solvents most of which are deadly, such as chloroform.
Some customers complained in the past about our o-rings swelling which we could never reproduce with ethanol gasoline nor grain alcohol nor ethyl alcohol. We expect those customers were cleaning their carbs with brake fluid.
This article was originally published in 2013 on our Product News Blog Nitrile (Buna-N) vs Viton® (FKM) O-Rings for a Gold Wing Carburetor The comments in response to that blog post provide more insight into this issue that you may find interesting.