ClassicCar

I've got a low oil pressure problem I hope someone can help me with. I purchased a used 8BA, rebuilt it (rebore, new cam, new crank & cam bearings, new helical gear oil pump, reconditioned the rods, etc.) and installed in my pickup two years ago. I double-checked all bering clearances during assembly. At cold idle, the engine had about 30 psi oil pressure and at cruising speed, about 45 psi. When warm the oil pressure dropped to about 10 psi at idle and 30 psi at crusing speeds. I immediately pulled the pan and re-checked the main & rod bearings - all within spec, and disassembled the new oil pump - it looked perfect. I put it back together and have driven it about 12,000 miles. A few days ago, it developed a low-end 'double-knock' and I pulled the pan. The mains are fine, but the upper rod bearing shells show wear, some to the copper. Fortunately, the crank is fine. The noise is a 'double-knock', and disappears above 2500 RPM - I don't think it's rod bearing noise. I'm concerned the cam bearings may also be damaged and plan to pull the engine apart (bummer!) I suspect the 'double-knock' may be wrist-pin noise, but won't know until I get it apart. Can anyone suggest why a fresh engine would have such low oil pressure? Any advice will be greatly appreciated.