About those exhaust valve settings…

Question:

In the June Mechanic on Duty you answered a question from a reader regarding valves and valve seats and their relation to unleaded gasoline. (“Is it time for new valves and seats?”) Coincidentally, the reader is from Scranton, Pennsylvania. I live in a town just outside of Scranton!

In your response, you said that you set the exhaust valves “one thousandth over” as a safety factor. Could you clarify this for me? The exhaust valve clearance for the Stovebolt Six in my 1940 Chevy is specified as 0.013” to 0.015”. I always set them to the nominal 0.014”. So do you mean that you would set them to 0.015” or 0.016”?

Answer:

That recommendation was for the exhaust valves on a Dodge flathead six. I advised the reader to set the exhaust valves one thousandth over because the exhaust valves on mechanical lifter engines can close up over time, and getting into the tappet case on the side of those engines to set the valves is much more of an ordeal than setting the valves on an overhead valve motor such as your Chevy.

Old Stovebolt sixes require more frequent valve adjustments, but the task is simple. Having owned several old Chevrolets of that vintage, I am familiar with the excessive tappet noise with those engines if the valves are adjusted too loosely. With those engines I would adjust the exhaust valves to open at 0.015” as specified, and then I would make sure I adjusted the valves at the recommended intervals specified in your shop manual. And then if the tappet noise is excessive I would revert to the nominal 0.014” setting.

I would also Permatex on only one side of the cork valve cover gasket so you can take the cover loose without damaging the gasket if you need to go back in to readjust the valves.