Date registered: Mar 2007
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The problems I have with this "test" are:
1. I don't have confidence that it was performed properly. In the description, they talk about replacing the bearing and then the race is "smoothed of any damage with emery paper." This cannot possibly be the correct way of performing the test. This test applies a line contact stress to the elements. In this kind of contact, microscopic "peaks and valleys" called "asperities" carry the load. When the load, on a micro level, becomes too great, the asperities weld together and then tear apart. This is called adhesive wear, and the wear scar on the bearings indicates that material has been torn away by this welding process, some of which winds up in the oil, and some stays deposited on the race. Some material is probably torn off the race, also. You can imagine that under the kind of line contact loading, the microscopic texture of the surfaces is critical. It is impossible to restore the surface of the race to an "as-new" condition by using emery cloth and some hand polishing. I would like to see the order in which the oils were tested... I wonder if the "best" oils were tested first before the race was all buggered up.
2. How long was each oil run at the various loads? Obviously the amount of wear is a function of time as well as load. And as time increases, the temperature of the metal and the oil will increase...
3. How smoothly were the loads applied?
4. The text tries to relate this type of testing to main and rod bearing lubrication. Nothing could be further from the truth, and it belies a total lack of understanding of what they were doing. Journal bearings (such as mains and rods) are full hydrodynamic bearings. The load is carried entirely by a thick film of oil that is built between the shaft and bearing by their relative motion. Except during starting, there will never be any metal to metal contact with any reasonable oil. Even oils that don't meet any of the API standards will work reasonably well in the bearings as long as the viscosity is right. The API standards deal more with thermal stability, detergency, ability to suspend wear particles without them clumping together, and camshaft wear... which is much more closely related to what this test might be demonstrating.
5. The API standards (SF, SG, etc...) are carefully established by consortia of engineers from all the major manufacturers. Each standard calls out numerous very specific tests that oils must pass to meet the standards. The tests are designed by the enigne manufacturers to simulate the oil's performance in various parts of the engine. I don't know if this Timken test is part of any of the API methods. If it isn't, then I wouldn't pay any attention to this test at all. If it is, then an oil's performance on the Timken test has to be weighed against it's performance in other parts of the standard. And of course the test has to be properly run, which I doubt this one was.
I wonder if there is a correlation between the oil performance results and the advertising pages for that oil in this magazine....
Royal Purple may be a wonderful oil, or it may be junk. This test doesn't shed a whole lot of light on the matter.