| Original engine build startup: Feb 2006. Current engine mileage: 94,500. I've been replacing rod bearings in my engine every 15K miles through this duration. I was originally running Mobil1 10W-30 for the first ~53K miles.
Each bearing replacement interval revealed heavy bearing wear through the babbit on the upper bearing shells and into the copper substrate, most notably on the #6 cylinder set. Changed up to 15W-50 Mobil1 and shimmed the oil pump pressure relief valve spring by 6.8mm by way of (4) 1.7mm flat washers installed into the bolt that retains the dual spring of this part of the assembly. The effect of these two changes resulted in notably higher oil pressures continuing into the higher RPM bands. Appx 95psi of oil pressure at 8500RPM vs ~70psi at the same RPM. 19K miles later, engine developed an odd rattle through the 2400RPM band, dropped oil pan. All of the rod bearings except for cylinder #6 were in perfect condition. Cylinder #6 showed only slightly more wear barely into the copper. Further inspection revealed that cylinder #3's wiseco piston suffered a catastrophic skirt failure, resulting in the audible noise observed. The bottom end was rebuilt with CP pistons. No other changes made. 22K miles later, cylinder #6 suffers catastrophic rod bearing failure. All 5 other cylinder rod bearings show minimal wear. During the rebuild to install CP pistons, a thorough rod journal diameter check was performed to test for any abnormalities in geometry. All journals spec'd out to no more than 0.0002" deviation except for cylinder #5 which had 0.0009" deviation in roundness. (Concerning at the time). Speculation is that there may exist some bias of lubrication flow to the #6 rod journal since this has always shown the most amount of wear in each bearing replacement. That journal had only a maximum of 0.0002" out-of-round in its geometry which seems to be about par for the course for our cranks, 0.0003" being the upper range. OR, there is more deviation in the geometry of the Pauter rod's big end lending to this but cannot be confirmed. Overall, while the #6 cylinder has always shown more wear than the others but all have shown a significant reduction in wear due to increased oil viscosity and increased high-RPM oil pressures, these changes have had a net positive effect on rod bearing service life. A new crank has been installed and bearing tolerances were increased from 0.0015" to 0.0018" this time around. In addition, I have also shimmed the oil cooler circuit valve by 1.7mm (a single 1.7mm thick 10mm flat head washer). Shimming the oil cooler circuit valve has produced an overall increase in oil pressure by about 15psi from what it was before. Observing the oil cooler temperature at idle reveals that the shimming of its control circuit has reduced flow through the cooler in idle condition but holding a steady 2000RPM produces enough pressure to provide flow through the cooler. This shouldn't pose any issues given the engine is not really producing much thermal load on the lubrication system at lower RPMs to warrant concern. Speculation is that the benefit to oil pressure increasing flow through the engine will help to keep the bearings/journals operating at cooler temperatures and lessen wear. Frankly speaking, we need higher viscosity oil to provide higher film strength between the rod bearings and journals to prevent film shear that allows bearing/journal metal-metal contact when pushing these engines well beyond their original performance outputs. In addition, we also need to increase the lube system's operating pressure (by way of shimming the relief valve and cooler circuit bleed valve) to provide ample oil flow through all of the engine bearing assemblies to keep the temperatures of these components down to appropriate levels for maximum service life. I'll report back in another 20K miles with the results of what shimming the oil cooler circuit valve has on bearing life. FWIW: 600RWHP on pumpfuel @ 570RWTQ, daily driven, beat to hell and back for fun.
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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