Normal Operation
Oil is drawn into the oil pump through the oil pump screen and pickup tube in the sump of the oil pan. Oil is pumped through the oil filter on the left front side of the cylinder block then enters the main gallery where it is distributed to the crankshaft main journals and to both cylinder heads. From the main journals, the oil is routed through cross-drilled passages in the crankshaft to lubricate the connecting rod bearings. Controlled leakage through the crankshaft main bearings and connecting rod bearings is slung radially outward to cool and lubricate the cylinder walls as well as the entire connecting rod, piston and piston ring assembly. The left cylinder head is fed from a drilling into the supply passage feeding the main gallery at the front of the cylinder block. The right cylinder head is fed from a drilling into the rear of the main gallery. Main gallery pressure is reduced as it enters the cylinder head galleries through fixed serviceable orifices, located at the upper part of the feed passages. It is this reduced pressure in the cylinder head galleries which feed the camshaft journals, the hydraulic lash adjusters and the primary and secondary timing chain tensioners. On Variable Camshaft Timing (VCT) equipped engines, the oil pressure feed for the VCT solenoids, VCT housings and camshaft phaser and sprockets is not reduced. The camshaft lobe and roller followers are lubricated by splash created through valve train operation.
This pinpoint test is intended to diagnose the following
- Excessive crankshaft end play
- Excessive main bearing clearance
- Excessive connecting rod bearing clearance
- Excessive camshaft bearing cap clearance
- Loose camshaft phaser and sprocket bolt(s) [ VCT engines only]
- Loose oil galley plugs
- Loose timing chain tensioner bolts
- Loose VCT housing bolts [ VCT engines only]
- Oil pump screen and pickup tube
- Restricted oil flow passages
- Worn or damaged oil pump