Posted by Dr. EVIL on November 16, 2015 at 00:39:55 from (70.194.132.106):
In Reply to: Re: Tractor oils. posted by animal on November 15, 2015 at 16:12:31:
Actually the removal of ZDDP from motor oil is OLD NEWS, 10+ years ago it was written up in HOT ROD magazine. RPM of the engine has absolutely NOTHING to do with cam wear due to no ZDDP. But valve spring pressure has EVERYTHING to do with it. High lift cams with cooresponding stiff springs have lot's of pressure between solid or hydraulic flat lifters and cam lobes. Rocker arm ratios even effect pressure.
Roller cams and roller rocker arms have no skidding wear surfaces so are immune from wear caused by NO ZDDP. My old 7.3L PSD engine in my '96 F-250 has roller cam followers & roller rockers from the factory so it's never needed much if any ZDDP. Engines with flat tappets like old tractor engines and small air cooled engines typically have soft valve springs and low ratio rocker arms for low wear pressure on cam lobes so lack of ZDDP doesn't really effect them much either.
The conventional 15W-40 ROTELLA T a in the white jug still has 1200 ppm of ZDDP according to Shell's answer man as of 2-3 years ago. Plenty of ZDDP to provide protection from wearing cam lobes flat in ANY engine. Even high lift cams in small block race engines running 10,000 RPM with dual & triple valve springs with 1000+# valve open spring pressure.
The failure mode has ALWAYS been a rather slow wearing away of cam lobes which causes the engine to misfire like it's out of tune. Engines suffering from no ZDDP have never blown up like thrown rods, spun bearings, etc. Some engines have been more sensitive to flat spotting cams than others, and certain vintage engines worse than others.
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