I = .008
E = .010
I use those figures as the absolute minimum. Rather have some clicking than burned valves.
It is strongly suggested you purchase an Owners Manual, Repair Manual, and the 1926-27 Chevrolet Service Bulletins. All of these items are available in reprint at a reasonable price.

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RAY Member Chat Group - Non-Geographical Region
Chevradioman http://www.vccacolumbiariverregion.org/If I had known that growing old would be this much fun---I'd have done it sooner!