The most likely source of oil in an engine cylinder is a leaking ring. Here's why:
1. Leaking Ring: The piston in an engine cylinder has rings that help seal the combustion chamber. If one of these rings is damaged or worn out, it can allow oil to leak into the combustion chamber. This can result in blue smoke coming out of the exhaust, decreased engine performance, and fouled spark plugs.
2. Bent Camshaft: While a bent camshaft can lead to issues in engine performance and timing, it is not a common source of oil in the engine cylinder. It is more related to valve and timing issues rather than oil leakage.
3. Faulty Oil Pump: A faulty oil pump can cause low oil pressure, which can lead to engine damage due to lack of lubrication. However, it is not a direct source of oil in the engine cylinder.
4. Fouled Fuel Injector: A fouled fuel injector can cause issues with fuel delivery to the combustion chamber, affecting engine performance and emissions. However, it does not directly contribute to oil entering the engine cylinder.
In summary, a leaking ring is the most likely source of oil in an engine cylinder, as it can lead to oil leaking past the piston rings and entering the combustion chamber.
