Ford Motor Co. announced Tuesday it is recalling 628,703 Ford Expeditions and Lincoln Navigators from model years 1997 to 2000 because of concerns of loosely bolted trailer hitches on the sport utility vehicles.

In some of the affected SUVs, customers already have had the bolts tightened after complaining of rattling in the rear of their vehicles, the automaker said.

If the bolts loosened enough to the point where they fell out, the hitch could separate from the vehicle - something Ford said has not happened.

There have been no reports of accidents or injuries attributed to the problem, Ford said.

Owners of affected vehicles will be notified by mail to arrange with their dealer to have the bolts and nuts replaced at no charge with stronger ones at a higher torque and with adhesive.

"With the summer trailer-towing season approaching, we want to encourage owners of these vehicles to have this work done before they tow," Ann O'Neill, the director of vehicle service for Ford customer service, said in a statement.