It will would be very difficult to reduce the page rank by simply putting up a temporary under construction page. The incoming links are what would keep the page rank high so those would typically keep your page rank in tact.
However, you want to be careful to take care of redirecting old page URLs to the new page URLs. A new content management system likely means you are going to be updating the urls to something new and more user friendly. Have your design team take care of using the .htaccess files on your servers to redirect your old pages to the new URLs. See the source below.
As long as you have good link structure on your new website, the search engines will not have a problem parsing the new site and creating the new search engine visibility based on what it finds. You should not expect to loose any page rank, especially if you take care of the redirecting procedures.
· 8 years ago