* Valve Train Components: While you've replaced the cam and lifters, there are other components in the valve train that could be the source:
* Pushrods (if applicable): The Contour's engine (likely a Zetec) might use pushrods. Bent, worn, or incorrect pushrods could cause tapping.
* Rocker Arms: These can wear, become misaligned, or crack, leading to valve train noise.
* Valve Guides: Worn valve guides allow excessive valve stem movement, causing noise.
* Valves: Burnt or damaged valves themselves can contribute to tapping. A visual inspection with the head off is crucial here.
* Valve Springs: Weak or broken valve springs can also lead to irregular valve operation and noise.
* Timing Chain/Belt: An improperly timed engine can cause valve train noise and even damage. Double-check the timing chain's tension and alignment, ensuring it's correctly installed.
* Other Engine Issues: While less likely after replacing the cam and lifters, consider:
* Low Oil Pressure: Insufficient oil pressure can lead to increased wear and noise throughout the engine. Check your oil pressure gauge.
* Engine Block Issues: In rare cases, a damaged engine block could contribute to abnormal noise, though this is less likely given your repairs.
* Piston Slap: While usually associated with a low-pitched knock, severe piston slap could be mistaken for valve tapping.
What to Do Next:
1. Professional Diagnosis: Given that you've already tackled significant repairs, it's time to consult a qualified mechanic. They have the tools and expertise to diagnose the problem properly. Trying further DIY fixes without a proper diagnosis could lead to more damage and wasted money.
2. Thorough Inspection: The mechanic needs to perform a complete inspection of the valve train. This likely requires removing the cylinder head for a thorough examination of all the components listed above.
3. Compression Test: A compression test can help determine if valves are sealing properly. Low compression in one or more cylinders points to a problem with valves or rings.
4. Leak-Down Test: This test helps pinpoint exactly where compression is escaping (valves, piston rings, head gasket).
In short, continuing to troubleshoot without professional help is unlikely to be fruitful and could risk further damage. The cost of a professional diagnosis will likely be far less than the cost of continuing to replace parts haphazardly.
