* No cold knock: The absence of a knock when the engine is cold rules out some issues, like a severely worn crankshaft or a major bearing problem (those typically knock even when cold).
* Developing knock with heat: This is the key indicator. The expanding metal as the engine warms up causes clearances to change. If there's wear in the connecting rod bearings, the increased clearance will allow the rod to tap against the crankshaft as it spins. Similarly, hydraulic lifters that are sluggish when cold might start to make noise as they warm and are supposed to adjust.
Possible Causes:
* Connecting Rod Bearing Wear: This is the most likely culprit given the description. Worn bearings allow excessive play, leading to the tapping sound. This is a serious issue and requires immediate attention to avoid catastrophic engine failure.
* Worn Piston Slapping: While less likely given the "tapping" description, worn piston rings or a slightly oversized piston could cause a slapping noise that increases with heat.
* Lifter Noise: Hydraulic lifters are responsible for adjusting valve clearance. If a lifter is sticking or worn, it might make a tapping noise, particularly as the oil warms and it struggles to maintain the correct lift.
* Valve Train Issue: Less likely, but a worn rocker arm or pushrod could also contribute to a tapping sound.
What to Do:
1. Do NOT continue driving: Driving with a potentially failing connecting rod bearing risks serious engine damage. The worst-case scenario is a rod snapping through the engine block, requiring a complete rebuild or engine replacement.
2. Immediate Inspection: Have a qualified mechanic inspect the engine. They should listen to the engine while running and possibly perform a compression test. A thorough inspection might include dropping the oil pan to examine the bearings directly.
3. Oil Analysis: Consider a used oil analysis to look for signs of metal wear particles that might indicate bearing failure.
Don't delay! This is a potentially critical engine problem. The longer you wait, the more damage you risk and the more expensive the repair will be.
