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Extract from an article "What's In a Camshaft". Autor Kris Wieber. The Shop Magazine, Dec. 2, 2009 :
Another factor that contributes to camshaft performance [life, added by KS] is oil. The lubricity of oil has been a recent issue for nearly all manufacturers of internal engine components.
"Motor oil has changed over the years, mainly with the removal of zinc-phosphates (ZDDP). The reason for the removal is because today’s new cars have roller tappet camshafts. Roller tappet cams do not require these additives that flat tappet (hydraulic or mechanical) camshafts need. Flat tappet camshafts require this extra protection because the lifter slides across the cam lobe. This metal-to-metal contact between the cam and lifter will not last long without this additive, especially during ‘break-in,’" says John Steely, sales manager for Howards Cams.
There are specialty oil manufactures, such as Brad Penn, that have this additive, he notes. But most of the common name brands (including Shell Rotella) no longer have zinc-phosphates at all.
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Is this common knowledge?
-Knut
Well, It is for me.
Actually the roller follower in gasoline engines came about because of the catalytic converter.
The converter requires elimination of the heavy metals like ZDDP to prevent failure of the converter. Once the ZDDP was reduced then cam failures became common. [around 1980] The quickest fix by the manufacturers was the adoption of the roller follower which does not need ZDDP.