A common misconception amongst many classic car enthusiasts is that modern oils don’t contain zinc, which results in a complete engine rebuild due to excessive cam and tappet wear caused by the lack of zinc. Some believe that to be safe modern oils should be avoided because they’ll destroy their car’s engine.
In 2004 American Petroleum Institute (API) changed their requirements of zinc additive and introduced new limits regarding it.
The API SN+ specification limits zinc to 800 parts per million (ppm).
The previous specifications, API SL and API SJ, didn't have specific zinc restrictions, but most oils available back then contained about 1,200 ppm to 1,600 ppm of zinc.
Zinc is an important element used in most oils because it acts as an anti-wear additive, which helps protect metal surfaces from the damages that could be caused by friction. Cam lobes, tappets, lifters, and piston skirts are the major components protected by zinc.
