Originally Posted By: CR94
Originally Posted By: fdcg27
... The problems with very thin grades therefore have nothing to do with the crank bearings but rather probably more with the timing chains, skirt wear and ring wear.
Everyone here seems more focused on the main bearings, where you won't find the excess wear anyway.
Agree. BITOG seems obsessed with engine bearings, which are in my limited experience one of the least troublesome critical components in non-abused vehicles. I've been acquainted with engines with a variety of other lubrication-related issues, but never a single bearing or oil pressure problem I can recall. Bearings are just easier to understand and simpler to analyze theoretically than, for example, the lubrication regime of rings or chains.
Rod bearings have, over the years, been a point of concern in certain engines. SBC's and SBF's with the non-351 firing order seem to wear the front bearings more than the rest. The "HO/351W" firing order (which is the same cylinder firing order found on GM's newer LS engines) resolved that issue and was, IIRC, one of the reasons for the change. Bizarrely, Ford went back to the Flathead firing order for the Coyote
But it wasn't just hot-rodded lo-po 302's, 289's and SBC's that were having issues with rod bearings at higher power levels, which people addressed, with varying degrees of success, using HV, HP and HV/HP oil pumps as well as heavier oils. And it wasn't like this "issue" was endemic. It was more a of premature wear thing, relative to the other rod bearings in the engine, exasperated by higher power levels. But BMW has, even in recent years, had issues with rod bearing longevity. Some of it can be placed on oil system design and track use but one of their major mitigation techniques (the success of which is debatable) was/is the spec'ing of quite heavy oil: 10w-60.
Shannow has shared in the past a paper by Honda about rod bearing design and the necessary change in width when going with these newer ultra-light lubricants. So bearing wear IS a concern, and a consideration, but certainly those other aspects of design are just as important. It's synergistic and thus the approach must be as well.