2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 92Get this manual
CHANGING THE ENGINE OIL ADJUSTING THE CLUTCH CABLE 17.Check: engine oil pressure
aSlightly loosen the oil gallery bolt 1bStart the engine and keep it idling until engine oil starts to seep from the oil gallery boltIf no engine oil comes out after one minute, turn the engine off so that it will not seizecCheck the engine oil passages, the oil filter element and the oil pump for damage or leakageRefer to "OIL PUMP" in chapter 4dStart the engine after solving the problem(s) and check the engine oil pressure againeTighten the oil gallery bolt to specificationOil gallery bolt 10 Nm (1.0 kg, 7.2 ft lb)