New Cast Iron Oil Pump pressure low

[alamow]

The pump was not changed during the rebuild earlier this year due to Covid lock down causing parts shipping delays. We ran the new pump for 4 weeks without issue except the engine brake would not operate on MAX if the oil pressure dropped below 31.5 psi.

Did an overhead, checked cam bearing, crank bearings, filters etc before finding the TSB on this forum. Cummins neglected to mention the TSB.

Oil temp is 220 f with maximum spikes to 240 f. Hauling 80 - 130t

Fitted the original pump to see if the oil pressure would return to normal. The pump has signs of wear and will need to be changed hence the question regarding shimming the pressure regulator on the new style pumps.

When installing the new pump we shimmed the backlash as per the manual. According to the TSB shimming is not required. Not sure if that would make a difference to oil pressure.