* Rod knock: This is a very common cause of knocking and is catastrophic. A connecting rod bearing has failed, allowing the connecting rod to hit the crankshaft. This will rapidly destroy the engine if driven. Do not attempt to drive the vehicle.
* Main bearing knock: Similar to rod knock, but the crankshaft bearings have failed. Again, this is a severe problem requiring immediate engine repair or replacement. Do not attempt to drive the vehicle.
* Collapsed lifter: Hydraulic lifters can fail, causing a knocking sound. While less severe than rod or main bearing failure, it still needs immediate attention. However, a collapsed lifter is less likely to prevent the car from moving.
* Wrist pin knock: The piston pin, which connects the piston to the connecting rod, could be damaged or worn, causing a knocking sound. This is also a serious issue. Do not attempt to drive the vehicle.
* Valvetrain issues: While less likely to cause the car to not move, severely damaged valves or rocker arms can make a loud knocking sound.
Because the car won't move and there's a loud knock, the most likely culprits are rod or main bearing failure. These are extremely costly repairs, often requiring engine rebuilding or replacement.
What you should NOT do:
* Drive the car: Continuing to run the engine will cause significant further damage and potentially catastrophic failure.
What you SHOULD do:
* Have the car towed to a qualified mechanic: Let a professional diagnose the exact cause of the knocking sound. They will likely need to remove the oil pan and inspect the engine bearings.
* Prepare for a significant repair bill: Engine problems of this nature are rarely inexpensive to fix.
Ignoring the problem will only lead to more damage and a much larger repair bill. Get it checked out as soon as possible.
