Plot problems (spoilers)

Helena knew the coordinates of the other half of the dial, at least clues to it, but had no intention to do anything about it before she met Indy. The Nazis knew it too, that was why they were already going there after getting the first half of the dial, but they didn't go for it before, instead they insisted to get the half of the dial Indy had first, which Nazis had no clue where it was.

The Nazis were following Helena in the beginning of the film, did not even know her connection to Indy, so why follow her? Voller had the resources of CIA and he followed Helena?

And about the continental drift, that is just ludicrous, because Archimedes traveled to the modern time, and got a watch, and went back, so of course Archimedes knew about the continental drift.

If that one was built to send someone to help then why did Archimedes separate the dial in halves and use code to hide it?

If he already went back in time, why not just bring back help? Wouldn't that be easier than leaving it to chances?

Another thing really mystifying was how Archimedes got an aircraft to pass through the time fissures since they were in the sky.

There are other plot problems, like how did a kid know how to fly an aircraft? But other people already raised them.