1. Check the valve clearances. The valve clearances are the gaps between the valves and the camshaft. If the valve clearances are too tight, it will prevent the valves from moving properly. You can check the valve clearances using a feeler gauge.
2. Inspect the camshaft. The camshaft is responsible for opening and closing the valves. If the camshaft is damaged or worn, it will prevent the valves from moving properly.
3. Inspect the valve springs. The valve springs are responsible for keeping the valves closed. If the valve springs are weak or damaged, they will not be able to keep the valves closed properly, which will prevent the valves from moving correctly.
4. Check the timing chain or belt. The timing chain or belt is responsible for synchronizing the movement of the camshaft and the crankshaft. If the timing chain or belt is worn or damaged, it will cause the valves to open and close at the wrong times, which will prevent the engine from running properly.
