That spring is usually retained by a pin driven through the pump housing. Tap the pin out, and slide the spring and plunger out. The plunger should slide freely in and out of the bore, with no hangups. Look for any debris in the bore, as well as any scratches or dings on the plunger. As oil pressure bears against the end of the plunger, it will compress the spring until a relief port is uncovered. Any excess volume of oil will be vented back into the oil pan. If a piece of trash gets wedged between the plunger and the relief port, the pressure will drop dramatically, starving the bearings. That sounds like what happened in your situation. Was the pump new with the rebuild, or was it re-used? I prefer to use a new pump whenever possible.
Jerry
