Is it bad linking to our main site from our company's small sites?

[newsphinx]

We owned 5 widget related sites, all are good in ranking in google SERP. Among the five we have one that most of our income is from. In order to let this main site rank well, we give it links from other four sites, but no back links.

Is it bad for us to do this?

[edited by: Robert_Charlton at 9:10 am (utc) on Feb 10, 2010]
[edit reason] examplified [/edit]

[AnkitMaheshwari]

IMO, as long as the sites have different IP's and the different contact info, it is perfectly fine. But do not indulge in site-wide linking.