Fuel Sediment Bowl Gasket - Cork vs. Neoprene

For the Model A Tudor

By Andy Wiedeman

August 2008

The Fuel Sediment Bowl serves to collect an rust or dirt particles which are transported from the gas tank by the gravity flow of the fuel between the tank and the carburetor. Prior to May 1931 the sediment bowl and fuel shutoff were located on the firewall. After April 1931, the fuel shutoff was located outside the passenger compartment and the sediment bowl was relocated to the carburetor. Before Mid 1929 all sediment bowls were cast iron, afterward a glass sediment bowl was an option. The remainder of this article applies to the glass sediment bowl type. The diagram below shows the action of this sediment bowl.

The fuel flows from the gas tank through a filter attached to the fuel shutoff valve, and then directly by gravity, through a large diameter tube, past the firewall to the sediment bowl. The fuel is injected into the bowl downward in the center of the bowl, causing a turbulent flow inside the bowl. Heavy particles are then collected in the bottom of the bowl, since they resist being forced upward through a flat brass filter screen and then to a small diameter fuel line to the carburetor, where it is again filtered by a cylindrical filter.

The sediment bowl is held in place by a bale under the bowl which tightens the sediment bowl against a gasket between the bowl and the fuel sediment bowl casting, using a threaded wheel. The small thread on this wheel prevents the owner from over tightening this assembly. The flat brass filter fits into a small recess cast into the glass bowl.

To prevent fuel leaking from the sediment bowl, a gasket is applied between the sediment bowl casting and the glass sediment bowl, just above the flat brass filter screen. The original Ford design of these gaskets were cork, and about 3/32 inch thick.

CORK vs. NEOPRENE Sediment Bowl Gasket

Two kinds of Sediment Bowl Gaskets are available. The first is cork as in the original design, and the second is Neoprene. The Model A owner must choose which type to use. Not much information is available for the buyer to make an informed decision. I can only tell you about my experience.

I was restoring the fuel sediment bowl assembly, and without knowing any facts about the gaskets, I simply asked for a fuel sediment bowl gasket. The supplier gave me a neoprene gasket, without any explanation or warning. I used the gasket, and it worked OK. However, after a tour, I needed to clean the sediment bowl. Since I had no reason to suspect a problem, I simply reused the neoprene gasket. After several days, I started the car in the garage and backed it out. With the car idling, I went to close the garage door, and then noticed gasoline pouring out of the bottom of the car, onto the driveway. Quickly shutting the engine off, I inspected the fuel system for leaks and found a huge leak at the fuel sediment bowl assembly. Upon disassembly, I found that the gasket had become soft and gummy. The gasket had extruded and become deformed enough to become unusable. A review of the compatibility between neoprene and modern day gasolines show that neoprene is not a good gasket material for this application. While it is OK for a single application, the gasket will become soft with gasoline and heat, and begin to deteriorate quickly, becoming soft and not able to be reused.

Research on the use of Neoprene (Details at the end of this article) reveal that the 10% ETHANOL additive in Colorado gasolines mandated by the Clean Air Act, combined with high temperature in the engine compartment is the culprit. [Note that the exhaust manifold is only inches away from the sediment bowl]. Refer to Appendix 1 for more detail.

Les Andrews, the foremost authority on the Model A, covers the restoration of the sediment bowl in his Model A Mechanics Handbook Volume I. He does not mention the use of Neoprene at all, but indicates that a “fresh” CORK gasket be used when replacing the glass bowl.

If you are going to use a neoprene gasket it is imperative that you replace the gasket after each use. This is a SAFETY issue. Having a leaking sediment bowl is inherently DANGEROUS and may cause a fire, or explosion. Since the fuel system is in such close proximity to the passenger compartment having less than a perfect seal between the glass bowl and the sediment bowl casting could be FATAL !!! In addition, the required replacement after every use, requires the owner to carry at least one, or preferably more neoprene replacement gaskets. While the CORK gaskets are less prone to this deterioration, it is still a good idea to replace this gasket after every use. Therefore, be sure to carry a replacement with you. While you may be able to “squeek by” if you are on a tour and don’t have a replacement cork gasket, this solution is really not practical if you are using a neoprene type.

Not all replacement gaskets and the flat brass filter screens have been manufactured in such a way as to be acceptable for use on the Model A Ford. Whilst, you may be cavalier and not think that these simple small parts are not very important, THINK AGAIN! Due to ability for these parts to cause a fire, or an explosion, it is important that high attention to the quality and the condition of these simple parts. An old cork gasket which has hardened due to heat and or time may become brittle and crack under use. If you remove the filter bowl and replace an old cork gasket, it may not seat properly, and under vibration become loose and begin leaking. New parts may not fit properly due to manufacturing. Read on …

Replacement GASKET & Brass Filter Screen Quality

The quality of the gaskets being sold as well as the brass filter screens are not very high at least from the supplier I bought from [Bert’s]. A comparison of the original parts with the replacement parts show that the Neoprene gasket was adequate for one use, but as shown above, it was deformed after one use. Note the out of round shape and the extruded fragment near the top of the gasket. While not shown clearly, the gasket was also cup shaped and not flat. Upon removal, the gasket felt gummy and soft, the gasket could be elongated and shaped easily. After drying out the used Neoprene gasket became hard again, but was deformed as shown above.

The reproduction flat brass filter screen had two defects. The hole punched in the center of the screen was off center by about .093 inches, and the hole was nearly 0.100 inch too large in diameter. The combination of these two defects allowed a gap to form at the edge of the filter and the glass bulb, allowing particles of rust to continue on to the carburetor. After assembly this is not easily seen because of the orientation of the sediment bowl on the firewall.

WHAT IS BEING SOLD

All of the major mail order supply companies and their respective websites have both CORK and NEOPRENE replacement gaskets for sale. Prices range from $1.50 down to $0.35. Most, BUT NOT ALL, of these mail order suppliers warn the buyer that the Neoprene gaskets are useful for one application only! Here is a table of what these suppliers say about the NEOPRENE gaskets.

Mail Order Supplier	Warning*	Comment in Catalog or On-Line
Mikes A-Fordable Parts	YES	Neoprene gasket should be replaced after every use
Snyders	YES	Neoprene Gasket can only be used one time.
MACsAutoParts	YES	Replace Gasket if bulb is removed
BRATTON	NO	Bratton does not warn the buyer about the problem with neoprene but instead claims that “Neoprene is more durable than CORK”
Bert’s Model A	NO	NONE … no warning … no information

* An explicit statement located with the advertisement for the purchase of the gasket, in the physical catalog or on-line catalog. Note that these warnings do not tell the purchaser about the effects of gasoline with an Ethanol additive, but simply tells the user to replace the gasket after each removal of the glass sediment bowl.

THE BOTTOM LINE:

For safety use a CORK gasket, and have a spare with you incase you need to clean out the sediment bowl while on a trip. Replace the gasket, even the cork one each time you remove the glass bowl for cleaning.

If you have a list of “What do I take with me on a Roadtrip?” add this gasket to your list. The MAFCA “restorer” Volume 52 – Issue 6 has extensive lists in an article by Bill Brigden, Dayton Ohio, but his various lists omit this important gasket.

Appendix 1

RESEARCH ON NEOPRENE and ETHANOL GASOLINES

The following information was gleaned from the Internet by searching Google using the following key words; neoprene, gasoline, ethanol

Colorado mandated the use of 10% Ethanol in gasoline, also called “Oxygenated fuel”, in order to comply with the Federal government’s Clean Air Act. The Clean Air Act calls for the use of fuels with added oxygen to reduce CO emissions. There has been much debate on the effect of this additive on engines, and engine gaskets made from neoprene. I could not find any research or testing information on the mechanical and sealing properties of Neoprene at elevated temperatures in the presence of gasolines with Ethanol additives.

Research on this subject on the Internet yielded:

· Neoprene is the Du Pont trade name for polychloroprene synthetic rubber. According to Du Pont, Neoprene has only MODERATE resistance [compatibility] with gasoline, and is mostly used for parts which undergo tension such as bladders and diaphragms [as in fuel pumps]. However, it is extensively used for seals especially for low temperature applications that need a flexible seal. Other sources claim that Neoprene has only “FAIR” resistance to gasoline. Whether Du Pont, and these sources indicate moderate or fair performance for gasolines with the Ethanol additive is not clear. There is considerable anecdotal evidence that gasoline with Ethanol reduces the compatibility with Neoprene.

· One source, ElastoTech Southwest Inc., specifically shows that their testing of Neoprene shows that it is NOT RECOMMENDED for use with petroleum fuels, especially those fuels with an Ethanol additive.

· ASTM testing of Neoprene, by several laboratories, show that there is SEVERE degradation of the sealing properties when exposed to Acetates, Benzines, and other chemicals and that MODERATE degradation can be expected when Neoprene is exposed to Gasoline, Kerosene, and Oils. The primary deficiency leads to softening and elongation under pressure or tension. Further tests show that Neoprene products show high degradation when exposed to gasoline with alcohol additives. I could not find any testing at elevated temperatures.

· According to most sources Neoprene is suitable for low temperature applications only. Neoprene should not be used in environments exceeding 200 deg. Fahrenheit. ASTM testing reveals that Neoprene has 100% elongation when exposed to 70 deg C [158 deg F] temperatures for 20 days. According to Du Pont the maximum temperature range of Neoprene is 300 deg F. However, Du Pont does not indicate the sealing properties or the mechanical properties of the material at this high temperature.

· The gasket and seal manufacturers claim “good” performance for Neoprene in the presence of Ethanol, but there are many claims by other informational sources that gasoline with Ethanol additives attacks the structure of the Neoprene and causes SEVERE deterioration. There are many Internet forum entries by auto and small engine owners which show that this degradation is not only real, but causes moderate to severe engine problems. The Automobile Mechanics Society of America claims that there has been an increase in fuel pump failures beginning with the introduction of Ethanol in gasolines.

· I could not find any reference to any testing of Neoprene under both high temperatures and simultaneously in the presence of gasoline with Ethanol.

· Ethanol is a solvent, and a drying agent which will extract water from gasoline. The Ethanol will interact with rust in your gas tank, causing flaking and etching of the surface. Very small particles thus released will be suspended in the tank fluid. One interesting feature of Ethanol that was listed on the Internet is that it is an effective solvent to remove neoprene deposits from furniture. Hummmmmm