When today's engines wear out, the most frequent symptom will be oil consumption. The usual culprit is infrequent oil changes which results in internal engine wear. What happens if the oil is not changed frequently enough is that the cylinder walls wear on the intake side and the piston rings don't clean the oil off the cylinder wall. The oil ends up being burned in the combustion process.
Bent valves caused by broken timing belt or jumped timing chain
This is another cause of internal engine damage. Usually the valves are bent when this occurs, sometimes the valve guides crack and also need to be replaced. In some extreme situations the valve will actually break apart and the stems can go through the pistons
Head gasket leakage, burnt valves and internal engine noises
Engine failure from internal engine problems doesn't happen as frequently as in the past. When checking for a leaking head gasket or a damaged or melted valves, we perform a cylinder leakage test. We pressurize the cylinders with compressed air and check first for excessive leakage, if the leakage exceeds 10% we will determine if its a valve or piston or cylinder wall wear. With internal engine noises we utilize our experience to isolate the location and probable cause before pulling the engine apart.