Is repairing the engine valve an overhaul?

When the engine is running normally, the piston can't touch the valve, but when the valve should be closed but it can't, the piston will touch the valve and bend it. This is called valve jacking. Not every car will push the valve when the timing is wrong, the belt is broken or misplaced.

Security risks:

Generally depends on the compression ratio of the engine. The greater the compression ratio, the easier it is to push the valve, not necessarily because the timing belt is broken. The valve cannot be closed because of carbon deposition, which may lead to the dislocation of the formal belt.