How long time for Google to remove dead links?

How long does it take for Google to remove dead links (404) and recrawl a site?

That's really back to Google, No one know what's the exact time to remove it, Ignore it until Google re-check it and remove it.

Yeah Marco, but it would be fun to know!

No one will know that, The time is different between forum to another, For example my forum is takes one month and another forum take 2 months so it's back to Google, Just forget it and keep working in your site focus in your content now.

It's never a set time. Google will continue to try all 404s until they deem it to be a permanent 404 and remove it from their index.