Knocks On Start-Up & Lasts A Few Seconds

The following conditions may produce engine knocks on initial start-up, but only last a few seconds:
^ Improper oil viscosity. Install proper oil viscosity for expected temperatures.
^ Hydraulic lifter bleed down. Clean, test and replace hydraulic lifter as necessary. When the engine is off, some valves will open. Spring pressure against the lifters will tend to bleed the lifter down. Repair the lifter only if the problem is consistent. Engines operated for only short periods between start-ups may have lifter noise that lasts for a few minutes. This is a normal condition.
^ Excessive crankshaft end clearance. Replace the crankshaft thrust bearing.
^ Excessive front main bearing clearance. Replace the worn parts.
^ Timing chain tensioner malfunction. Clean, inspect and replace the timing chain tensioner, if required.