Re: 359 Straight Eight Engine

Posted by Rusty O\'Toole On 2010/12/26 18:03:42

I also question the necessity of special oil in a flathead engine.

The reason modern engines do not require zinc is that their OHC valve trains are short, light, and lightly loaded. The old pushrod OHV engines had a heavier valve train and stiffer valve springs and consequently, more pressure on the cam and lifter surfaces.

A flathead has similar light valve train, light springs etc to an OHC.

In fact I believe the use of zinc began in the early fifties after a spate of cam and lifter failures on the then new OHV engines, particularly Studebaker and Chrysler although other makes were not immune. This was something new as the old flatheads had never experienced such cam and lifter failures.