Quote:
Originally Posted by arctictraveller
Lifters can clatter, but I never heard one knock. That's usually something more serious like a rod or main bearing. Either one of these can be caused by low oil pressure, has that been checked with a mechanical gauge? If a lifter is bad, the cam will need to be checked too. If your mechanic is certain its a rocker arm, will he gaurintee it will fix the problem? Before sinking a ton of money into that engine, consider the cost of a replacement, low mile used one. These motors are known to go hundreds of thousands of trouble free miles, but once in a while one goes South prematurely, so I wouldn't be afraid of a used one. I'd get another opinion. Best of luck
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+2 (sort of) ---- a bad lifter can definitely make a sound that *approaches* that of a knock....but I agree, the description of that sound seems more like a rod/bearing issue or perhaps piston slap.....
HOWEVER:
A rod knock usually gets LOUDER as the engine warms up though (as the oil heats up and thins out). And since the OP stated that the sound gets *quieter* as the engine warms up....not sure that the described symptoms make immediate sense as a rod bearing issue.
On the other hand:
A partially-collapsed (bad) valve lifter
will usually become *more quiet* as the engine runs longer ---- as the hydraulic cavity within it finally "fills up" and takes up the valve-lash clearance that is causing the clattering in the valvetrain components.
aaaaaand also:
Knocking noise at startup that's caused by piston slap can also get quieter as the engine warms up (the piston heats up and expands enough to close down its tolerances within the cylinder bore.)
As others have said, good luck! It's always a valuable learning experience, whatever the outcome.