Need to shorten and change site-wide meta titles (50.000 pages). OK to do all at once?

[lcourse]

Just noticed that google completely screws up our meta titles in the SERPs. Google decided to show titles which are not understandable to visitors and worst of all even shows titles in different  languages than the actual page. The words of the displayedf titles are nowhere on the page (actually they are parts of old title tags that we stopped using 6 months ago and that we used on different pages). Pages are crawled weekly.

All our meta titles are a bit longer than the 70 character limit, so I plan to rephrase and shorten them so that they are all max. 66 characters. Dynamically we choose different variations of title texts based on character length of keywords.

Having titles that fit into SERPs without cutting are supposed to have less probability to be changed by google.

I heard some people reporting loss of rankings after site-wide meta title changes. Especially since we changed title tags sitewide already about 6 months ago I am a bit concerned.

How would you  proceed? Just do the site-wide change all at once?

[TakeshiYoung]

The title tag is one of the most important tags on your page, from a search engine perspective, so I would proceed with caution. You might want to start with a smaller set of pages to see if it has any impact on search rankings, and be ready to revert to your old titles if there is any negative impact. Also, make sure that there are no duplicates among the 50K title tags.

[lcourse]

Takeshi, thanks.

How long would you wait and monitor ranking changes before to roll out sitewide after first test?

Not sure whether keeping changes to minimum will reduce risk (so mainly shortening without much other improvement/changes)?

Titles are all unique.

[TakeshiYoung]

It depends how fast your site is crawled. See what your crawl rate is in Google Webmaster Tools, vs the number of pages you have. Manually check to see if the pages you updated have been cached, and wait a few days after that.

[RepLoc_Tim]

Based on your description, there are serious problems in how the Title is displayed in the SERPs (wrong syntax and language).  If this is the case, you need to fix that immediately.  If not, you will likely suffer a bigger problem - no clicks and your CTR plummets (a trust factor).  You will start dropping out of the rankings fast if you competitors are getting those clicks.  Nobody clicks on faulty titles because it often is tied to a faulty site.

I agree with Takeshi that normally you would want to segment and test before committing to a massive overhaul, but it sounds like you are in a more urgent situation right now.

[lcourse]

thanks Tim. 
started launch of new shortened optimized titles today for most important pages.