Seems quite human.
Edit: your the guru, why is there no evidence of hx bearing wear from you? I imagine that you have pulled a motor apart that had them in it.
If you mean ACL HX bearings, I have never seen or touched an ACL bearing until the two sets I purchased showed up this week. They may be more popular overseas for S65 and S85s, but not very much in the US.
I purchased two sets (H and HX) which I intend to take measurements on with actual metrology, not Plastiguess. Sunnen GA-2121 with CF-502 setting fixture calibrated against an NIST certifed calibration ring.
My intent is to take a set of readings on H, HX, and a half mixed set which I honestly hope will provide the clearance which matches the ratio recommended by the most prominent and long standing bearing manufacturers.
I have opened 6 engines now with rod bearings that have a larger than OEM clearance and not one of them showed the starvation derived wear pattern described by Clevite. Lets be realistic, the bearing manufacturer is irrelevant, the physics behind it are what matters. One engine was a Dinan stroker and the crank rod journals were manufactured and measured to be .0004 smaller than the OEM crank. One engine was an OEM crank I had reground and polished .0005" undersized. Two were BE bearings/stock crank at 5134 miles and 12k-ish miles. The other was a VAC coated (extra clearance)/stock crank motor at unknown mileage (spun main bearing S65, some time after rod bearing change - S65s are somewhat prone to #1 main failures).
Not one of those engines showed starvation wear, but all showed even wear across the bearing face in the axial direction up to about 1/2" from the parting lines.
I have also removed a set of OEM 702/703 bearings on a stock crank S85 (my own car) with 14k miles on them. These were changed out at 68k miles when I had a stuck injector. The car ran M1 0W-40 the entire 14k miles since bearing change with a 3k OCI and religious warm up routine. Two toddlers in the back for 80% of those 14k miles so no silliness driving. Those bearings *did* exhibit the starvation wear pattern.
While that was only one data point and you can't determine a trend with one point, it was enough for me to say that lowering viscosity alone would not solve the problem.
So, honest questions for those who believe that you can't have too much clearance:
- What would be the engineering purpose for choosing tight oil clearance on a hydrodynamic plain bearing?
- What detrimental effects exist to using excessive clearance *aside* from pressure/flow concerns
- What is the piston to wall clearance specification from BMW for the S65 and S85?
And one more for good measure:
- What are the temperature coefficients of expansion for the engine block and pistons?