Why must valve clearance (jarak injap) be checked and adjusted periodically on a four-stroke motorcycle engine?

1. Incorrect clearance can cause valves to not seat properly or open at the wrong time, reducing performance and potentially damaging the valve or seat
2. Valve clearance has no effect on engine performance
3. Valve clearance only needs to be checked once, at the factory, and never again
4. Valve clearance is only relevant to the cooling system