Is zinc oil really necessary for our engines

[Per Lundgren]

You can read in many places that it is necessary to use engine oil with a high amount of zinc and phosphorus in our engines in order for the camshaft and valve lifters to survive. But is this really necessary? Here is the reason I wonder!

In 2012 I sold my 1972 BMW 3.0S with 750000 km (466000 miles) on the odometer (6 cylinder 3 liter engine with overhead camshaft). These M30 engines were known to have problems with worn camshafts and rocker arms. I replaced the camshaft and rocker arms several times.

The last time I noticed pitting damage on the cams it increased rapidly over a period of 4-50000 km (20000-25000 miles) and I was prepared to replace the camshaft once again. But before that I changed from mineral to synthetic engine oil.

Much to my surprise, the pitting damage had not increased at all the next time I checked the camshaft. Then I drove 200000 km (95000 miles) and the camshaft pitting damage only increased very slightly over all those miles. Apparently, for that car's camshaft, synthetic motor oil was much, much better than mineral oil.

So wouldn't it be better for our Porsche 356 engines to use synthetic motor oil instead of old fashioned mineral oil with high zinc and phosphorus content?

[David Jones]

Some of the synthetic oils have high (1200 ppm) ZDDP content, specifically those with high viscosity such as 10/40 or 20/50. That is what I use.

[Martin Benade]

Pitting damage sounds more like a corrosion problem than a wear problem.

[Per Lundgren]

My pitting problems was definitely not korrosion.

[Al Zim]

In 1962 when I started working as a mechanic our shop used Kendall oil. It has a heavy dose of Zinc in it because the cars needed that. Oil from Bradford Pennsylvania had the best oil for making superior engine oil. Kendall could no turn down the offer from Phillips to purchase their name. In the meantime Kendall made a 20W50 oil which Ed and I started using in the late 60's. Still with high Zinc. THE BRADFORD PENNSYLVAINA OIL STILL COMES FROM SUPERIOR WELLS. The name has change a couple of times the mixture has improved!
Each engine that we rebuild has two Brad Penn (new name) break in oil changes. The first change is after a few (2 or 3) hours of running. It is drained and the full flow filter is changed. It receives another change of Brad Pen BREAK IN OIL . OIL changes on older Porsche's always get high Zinc. WITHOUT A FULL FLOW OIL FILTER ON YOUR ENGINE YOU SHOULD ALWAYS DO AN OIL CHANGE BEFORE 2,000 MILES AND A FULL LUBRICATION ON THE CHASSES AT 1,000 MILES.
You have already explained the pitfalls of engine wear. On the 356/912 replacing the camshaft is expensive. It is the first part installed within the engine assembly. Some technician has overhauled your engine in their garage. al zim

[Martin Benade]

I don’t see how a flat lifter can have a protrusion that scoops metal off the cam lobe to form a pit and then becomes flat again so that it doesn’t eat up the whole lobe.

[Don Gale]

Hertzian stress

[Martin Benade]

I read up on that a bit. I ran into lots of math that was beyond my understanding so I couldn’t tell if this was a micro force or a strong one. Could that pull metal out of a cam leaving pits?

[Wes Bender]

I have owned several BMWs and excessive wear in the valve train seemed to go with the territory, however I never used synthetic oil in them. One instance of synthetic oil seemingly solving the wear problem in a BMW engine isn't a very large sample if you are trying to argue that zinc isn't needed in our 356 engines to prevent wear. Do you have any other definitive studies to back the theory? It's my understanding that the main reason for removing zinc from motor oil was to prevent damage to catalytic converters, a device we don't have on our engines.

[Don Gale]

I read up on that a bit. I ran into lots of math that was beyond my understanding so I couldn’t tell if this was a micro force or a strong one. Could that pull metal out of a cam leaving pits?

Yes, that's the nature of Hertzian stresses. Highly concentrated forces on a small contact area (line contact in the case of cam lobes) can cause localized areas to exceed yield and blow out craters over time due to fatigue. Same here, the math is way over my head anymore, but we did study this in class some 50 years ago -- where did the time go? If you have an old failed roller bearing sitting around, take a look at random pitting on the rollers. My professor mentioned back in the day that sitting static in one place caused even more damage and that brand new cars from the factory could fail roller bearings during transport via rail, not caused by poor lubrication nor corrosion.

[Martin Benade]

Would zinc have any effect on the Hertzian stress damage?

[Don Gale]

Would zinc have any effect on the Hertzian stress damage?

Zinc rich oil helps protect the cam from sliding friction, especially critical during break in. Hertzian stresses will be present somewhat independent of type of oil. Viscosity, oil quality, and more frequent change intervals will reduce pitting due to stress corrosion. Weaker valve springs would offer better protection at the expense of reduced redline. Cam design is very intricate and many factors affect their longevity.

[Harlan Halsey]

No one really knows. All VW and Porsche engines were designed after ZDDP was universally added to engine oils. ZDDP was removed from the thinner grades of engine oils which new cars use because with ZDDP catalytic converters couldn't meet a US government requirement that converters last at least 50,000 miles. New camshafts inexplicably failed in a couple of English sports car engines and the failures were attributed to the lack of ZDDP. As usual, panic swept enthusiasts, and we all either added ZDDP or switched to 50W oils which never had the ZDDP removed. Some oil companies began reporting ZDDP concentrations in their oils. Some resisted. To my knowledge no one has reported a camshaft failure in a 356 thought to be due to a lack of ZDDP.
If 10 volunteers with good running 20,000-mile 356s would switch to say 30W non ZDDP oil and report camshaft wear at 50 and 75,000 miles, we might actually know.
I will await the results, but I'll stick to 15W50 Mobil 1 and SWEOCO 20W50. because I think those weights are superior anyway. The consensus seems to be that about 1300 ppm is right.

[David Jones]

Harlan. I'm sure you actually meant 1300 ppm not 13

[Harlan Halsey]

Harlan. I'm sure you actually meant 1300 ppm not 13

Right, thanks David.