How long after a URL starts showing a 404 does Google stop crawling?

[AndrewMiller]

Before hiring me to do SEO, a client re-launched their site and did not 301 the old URLs to the new. Only the home page URL stayed the same.

For a month after the re-launch, the old URLs returned a 404. For the next month, all 404 pages (basically any non-existent URL) were 301'd to the home page. Finally, 2 months after launching, they properly 301'd the old URLs to the new.

Now, the new URLs are not ranking well. I assume it's too late to realize any benefit from the 301's, just checking to see if anybody has any insight into how long Google keeps trying to crawl old/404/improperly 301'd URLs.

Thanks!

[RyanKent]

Google's crawlers follow links. As long as links exist, those links will be crawled, even if the link generates a 404 error. They could choose to follow known 404 links less frequently, but they will still make attempts to follow the link.

[SEM-Freak]

Agree. Google will follow the links. Keep checking webmaster tools and 301 the pages Google can't find. I can't see why you would not get the link value.

[AndrewMiller]

Thanks for the responses. I tend to agree, but my concern is the "permanent" nature of a 301. I assume they will re-crawl the old URLs and replace the previous redirects with the new ones eventually.