Reply to "roller camshafts"

As for the non-recommendation of synthetic oil with roller cams, it may stem from the U.S. DOT pressuring all the big oil companies to remove the heavy-metal additives that allow protection for very high pressure sliding contact-e.g- aftermarket flat tappet bottoms against cam lobes. Heavy metals such as zinc and phosphorus poison catalytic converters, so they're now gone with tetraethyllead in the name of smog control. In street engines with roller cams, the rollers tend to skid over the cam lobes at low engine speeds, not roll, so the problem is the same as with flat-tappet cams- the rollers flatspot and the lobe tips wear. Stock hydraulic rollers run fairly mild springs so the skidding/flatspotting isn't so damaging. I'm told that MOTORCYCLE full-synthetic oils have yet to be reformulated (only a few bikes now carry cat-converters), so Silkolene and some Motuls (both from Europe) can still protect against high valve spring pressures while giving one the extra 25 degrees of temperature protection of synthetic oils.