What could cause a loud knocking in my car engine

knocking or clanging usually means engine rebuild or replacement
What is piston rod knock Engine Knocking Yahoo Video Search Results 3 Causes of Engine Knock

in the engine --- failed big end or main bearings

possible but I would suggest a compression test to check for loose valve seat insert. They can come loose and follow the valve up and down and cause loud knocking noises and faulty engine operation.

Bent valves would be number one cause. Check the timing. If you lost time, your valves are tapping the pistons causing the knock. When the valves tap the pistons they bend and don't close all the way, so the cylinders cant make compression.

By looking for another engine or Vehicle.

Sound like you have spun a bearing do to a blown head gasket. Does the oil on the dipstick look almost like a chocolate milkshake in color? If so your coolant has reached the oil pan and that can definitely cause the engine to spin a bearing causing a loud knocking sound.

if something wrong with water pump vehicle can and will overheat which can cause minor to extreme motor damage such as blown head gasket --warped heads--****rod knock****seized engine loud knocking usually means lower end damage to engine which can be from engine rebuild to engine replacement

Ticking is generally associated with a valvetrain problem but may be caused by low oil level or pressure. Noise is in the upper half of the engine. Knocking is from low oil pressure and is caused by worn bearings causing pressure loss. Knocking is the worse of both conditions (means overhaul or engine replacement.) Ticking needs to be checked for it's cause...if cause is low oil pressure, remember...oil pumps don't cause low oil pressure, pressure will lost if bearings are worn or pump inlet screen is plugged with carbon.

Here's what you don't want to hear...A loud knocking noise from inside your engine is generally caused by a crank or rod bearing...when caught very early, sometimes they can be replaced. however, once the noise is loud, the attending crankshaft journal gets "hammered" out of shape and the job becomes very expensive and in most cases more costly than engine replacement. There is one other item that can cause a loud knock...your flywheel. Bearing problems generally cause low oil pressure. If you have that, it's gone...if not, have the flywheel checked before sending the engine to the scrapyard.

noise is caused by lack of oil to lifters, or worn timeing chain. if noise is from lifters it should go away wit proper oil level, if still there needs timeing chain.