As it was explained to me they did run A-B comparisons of coated and non coated lifters on the Spintron. During the “abusive testing” phase several extreme conditions were tested. One test condition was excessive spring length above coil bind. During this test the uncoated lifters showed significant failures, while the DLC coated lifters showed no failures. Over the various test conditions, this was the #1 source of lifter failure meaning that more uncoated lifters failed here than any other test condition.
This effect is often called spring surge. To give an example, installed height specs for a spring might call for a minimum of .050” above coil bind, and a maximum of 0.100” above. The “abusive test” would have a number much larger than the 0.100 maximum, say for example 0.300”. It is fairly common to have builders exceed the max number, because “more is better, etc.”.
This causes harmful ocillations in the spring which (when multiplied through the rocker arm ratio) transmit percussive forces directly to the lifter face. You can find high speed videos online showing this, but basically this creates a jackhammer effect and tears up the lifters.
This is not an explanation for why every flat tappet cam in the world has failed. It is a conclusion of a very specific test which has some useful conclusions
I believe the way to think about DLC coating is to consider it as an insurance policy, if (and when) something goes wrong in the valve train, the coating can provide substantial protection and possibly avoid a catastrophic failure. There is no one saying the cams or lifters are too soft, and for sure coating a dimensionally flawed lifter after the fact does no good.
Quote:
Originally Posted by Shiny
Yes the video makes an argument but I don't think you can extrapolate to DLC. A typical hardness test uses an indenter that penetrates quite a bit. DLC coatings are so thin, would they even affect a typical hardness test? I suspect the indenter would just crush right through it. .
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Yes, 100% right, DLC is around 10 microns thick, way too too thin to measure using standard Rockwell testers, which are designed for materials that are through hardened. Even case hardened parts (like cams) can be a problem if the case depth is too shallow.