Oil grade

quote: Newer oils have reduced the amount of zinc, and can actually be harmful to old engines unless a zinc additive is combined with the oil. I believe 1000-1300ppm is the ideal range for zinc.

Mobil 1 V-Twin contains 1700 ppm Zn.
Mobil 1 Racing 4T 15W-50 contains 1200-1300 ppm Zn (an independent lab measured 1315 ppm)

quote: Viscosity retention is why synthetic oils can go up to 25,000 miles (40,000KM) in some applications. For 3000 miles or less between oil changes, the difference is negligible.

I don't think this is true. Mineral oil begins to degrade immediately. The tabel I referred to shows high viscosity retention losses after only 800 miles.

In an older engines with flat tappets,

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I know I'm a bit thick on this subject and I'm sure there a reason why. But, modern motors have flat cam followers gear and chain driven cams, running at very high RPM and there's more of them too. Don't forget some are wet sumped with the engine oil used in the gearbox. Is it just the heavy loads caused by very strong valve springs? But then again my A series minis never any issues with oil failure. :?

Cash