What is the method to distinguish between the top dead center of cylinder one and cylinder four?
2 Answers
If it is turned to the top dead center of cylinder one or four. The cylinder where both valves have clearance is the one in the power stroke. There are marks on the camshaft and crankshaft, assemble according to the marks. The cylinder where both the intake and exhaust valves are completely closed, which is the lowest point of the camshaft, is in the power stroke.
Having spent over a decade in the repair shop, the most common method I use to distinguish between TDC (Top Dead Center) for cylinder 1 and cylinder 4 is by rotating the engine crankshaft and interpreting the timing marks. On most four-cylinder engines, TDC for cylinder 1 typically serves as the ignition reference point, while cylinder 4 may be in a different stroke state. I rely on a timing light aligned with the crankshaft pulley scale: when the pointer hits the zero mark, if the intake valve is closed or there's strong compression feel at the spark plug, it's likely cylinder 1's position; if there's no compression feel, it might be cylinder 4 in the exhaust stroke. Simultaneously, I check the camshaft position sensor to see if the cam lobe aligns in a specific direction. Misjudgment can lead to ignition timing chaos or even valve damage, so I always recommend consulting the repair manual or online resources first to confirm the firing order. The entire process requires patience—rotate slowly to prevent piston-to-valve contact, ensuring safe and efficient repairs while prolonging engine life.
