Can the valves hit pistons on a 98 jeep 4-cylinder engine?

Yes, the valves can hit the pistons in a 1998 Jeep 4-cylinder engine if the timing is off, a valve spring breaks, or there's significant internal damage (like a broken connecting rod). These engines, like many others, are not interference-free. This means that if the valves and pistons occupy the same space at the same time, damage will occur.