Depends on pre-delivery treatment. Subaru dictate a short first change interval -3000mi/5000kms, where normal change is 12500kms. Some makers give their engines a sort of run-in process before they leave the plant. There is lots of noise out there about rebuilt Jag engines being prone to issues from using modern oils with low zinc, quoting their use of ‘flat tappets’ as significant. I find this confusing as there are still many modern engines with flat tappets (as distinct from roller tappets) that seem ok with modern oils. Whatever, I run Penrite 10-50(1200 ppm ZDDP) in my older cars.
jp
At this point, that’s all I take it as: noise.
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It’s not just that the tappets are flat. It’s also a function of the valve spring rates, the cam profile, and other factors.
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Indeed, and on an XK, and presumably on a 12 (though I am unaware of how much spring pressure they’re set with), the low spring pressures, and mild cam profiles, I just don’t necessarily see an issue.
Tweety’s cams and tappets, upon its last inspection before I sold it, and in addition to the ~160,000+ miles they had on them, had accumulated an additional ~10,000 miles, with whatever Brand X, on-sale oil I used, and they looked fine.
Only one example, I’m aware, and far from definitive, but… I’m still researching. Next, I’ll pull the cam cover off of Margaret, and see how those loves and tappets look.
In the grand scheme of ‘old engines versus modern oils’ I’m betting the number of actual engine failures is very small, at least if measured on a percentage basis.
Some amount of increased wear during the overall lifespan of the engine is a different consideration. In the case of hobby cars that typically don’t accumulate a lot of miles, perhaps an entirely academic one.
Cheers
DD
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