Yes, the clearance gets smaller and the valve spring gets longer. If the valves are not adjusted, they start to leak because when the clearance is gone, the valves cannot close tightly.
How did those old engines run without EGR valves, catalitic converters, electronic ignition, throttle sensors, computers, electronic fuel injection, etc. That's why I like my MB Diesels: most of the latter parts are not used and therefore can't fail and I can fix almost anything myself. I think that $50 - $60 an hour to have my car repaired is obsene. They should arrest people who charge this much for obsenity, not the dancing girls!
P E H