Hi Guys in the past i had 4 sites pretty much selling the same thing but targeting different keywords.
2 of the 4 sites had a partial penalty
Unnatural links to your site—impacts links Google has detected a pattern of unnatural artificial, deceptive, or manipulative links pointing to pages on this site. Some links may be outside of the webmaster’s control, so for this incident we are taking targeted action on the unnatural links instead of on the site’s ranking as a whole
I have cleaned both up and had penaltys revoked
Basically i want to add all the sites together so i was thing thinking of 301 site A, B, C, to site D and concentrate on making a very authoritative site combined opposing to having 4 sites competing against each other
Topic header: "301 to home page" Question in body of post: "Is it bad practice to 301 multiple sites"
That's a huge difference. Are you planning to redirect all requests for the old sites to one site's front page ... or will there be page-for-page redirects from each page on the old site to an equivalent page on the new site?
Don't do a single redirect directing all traffic from your old site to your new home page. This will avoid 404 errors, but it's not a good user experience. It's more work, but a page-to-page redirect will help preserve your site's ranking in Google while providing a consistent and transparent experience for your users. If there won't be a 1:1 match between pages on your old site and your new site (recommended), try to make sure that every page on your old site is at least redirected to a new page with similar content.