Bardahl Classic Oil SAE 40 is a 100% mineral unigrade engine oil designed for lubrication of gasoline engines from 1900 to 1950. SB Service API Specifications. Bardahl Classic Oil SAE 40 oil contains a minimum amount of additives and is fully compatible with brass, bronze, copper and non-ferrous metals. The viscosity chosen for vintage engines provides constant oil pressure, which contributes ad a minimum oil consumption. It is suitable for sealing materials of the time (paper, felt and fabric). The excellent adhesion of the lubricating film ad to ensure minimal engine wear at start-up, even after a prolonged downtime. Suitable for vintage cars and motorcycles from 1900 to 1950.