Lead… Anyone? – Dave’s Garage

This month we dabble with valves and the myth that we need leaded gas for our older cars designed to run on leaded gasoline. The question comes from our own Wendell Noble with a question about his car.

Dr. Dave, Ever since lead tetraethyl was removed from gasoline, I’ve been unconcerned about what detrimental effects on my old car engine might result. I figure, what the hell, it’s not like I’m entering races with my car. This past fall, I noticed my engine was missing on one cylinder. It turned out I had an obviously burned exhaust valve on number one cylinder. Does this mean I should rethink things and start using a lead substitute additive? Can I blame the lack of lead for my valve problem? At least I learned how to do a valve job. -Wendell

Wendell, the short answer is no, you do not need to add a lead additive, and no, you do not need to rethink anything. When you do the valve job, talk with the machine shop to find the best solution for you. You will need to install modern valves made from hardened steel. You may or may not need to install hardened valve seats. This depends largely on the material the head is made of. The reality is that valve most likely would have burned eventually, even on leaded gas.
Now, lets discuss the whole lead story. First, some history:

In 1919, Dayton Metal Products Co. merged with General Motors. They formed a research division that set out to solve two problems: the need for high compression engines and the insufficient supply of fuel that would run them. On December 9, 1921 chemists led by Charles F. Kettering and his assistants Thomas Midgley and T.A. Boyd added Tetraethyl lead to the fuel in a laboratory engine. The ever present knock, caused by auto-ignition of fuel being compressed past its ignition temperature, was completely silenced. Most all automobiles at the time were subject to this engine knock so the research team was overjoyed. Over time, other manufacturers found that by adding lead to fuel they could significantly improve the octane rating of the gas. This allowed them to produce much cheaper grades of fuel and still maintain the needed octane ratings that a car’s engine required.

Subsequently, it was noticed that valve wear was reduced. Specifically, valve seat recession was reduced. Before leaded gas, exhaust valves would become so hot, they would temporarily micro weld to the valve seat, when the valve opened, this micro weld would open, causing a poor seal, valve seat regression, and eventually a burned valve or valve seat. The addition of lead formed a micro film of lead on the valve seat and valve, largely preventing this from happening.

It is estimated that 5,000 people were dying annually, with many more thousands falling ill due to the effects of lead poisoning.

What does all of this mean to the antique car owner who has a car designed to run with leaded gas? I would suggest continuing to drive the car and adding nothing to the gas. If there is a problem with a burned valve, replace the valves with modern, hardened valves when it is time to do a valve job. The valves on the older engines were prone to failure due to the materials available at the time of manufacture. While the lead did help, it’s effect was marginal at best. Remember, the purpose of the lead was to improve the octane rating of the gas Inexpensively, not to lubricate the valves.

Drive the car, enjoy it. If it needs a valve job, upgrade to modern valves and be done with it.


Please email all inquiries to: Dave
or snail mail
32 Turkey Hill Road
Richmond VT 05477

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