Ahead of the Bell: Diversified manufacturers

Prospects for a prolonged earnings downturn and credit destabilization led an analyst Tuesday to cut his ratings on shares of a mining equipment maker and a farm equipment maker but raise his ratings on shares of a diversified manufacturer whose earnings should better withstand the turmoil.

Goldman Sachs analyst Terry Darling cut his ratings to "Neutral" from "Buy" on shares of South Milwaukee, Wis.-based Bucyrus International Inc., which makes mining equipment, and Duluth, Ga.-based AGCO Corp., which makes farm equipment.

The analyst cited Goldman Sachs' economic and commodity forecasts indicating the sector will experience earnings declines of 10 percent to 21 percent in the next two years.

Darling also raised his rating on shares of New York-based Dover Corp. to "Buy" from "Neutral" because of Dover's "more defensive earnings profile."

He reiterated his "Neutral" rating on the entire sector "as our coverage is down 57 percent since the 2007 peak" and "classic signs that the bottom is nearing."

In premarket trading, shares of Bucyrus rose $1.68, or 5 percent, to $35.61 and AGCO shares rose $1.27, or 3.4 percent, to $38.88 while shares of Dover were unchanged.