Three years ago, Volvo invested $150 million in plant upgrades.
The engine-block machining line was announced Thursday along with a Mack Trucks restructuring plan that includes moving Mack's headquarters from Allentown, Pa., to Greensboro, N.C.
Volvo Powertrain's Washington County plant makes truck engines and transmissions for Volvo and Mack.
Volvo, which is based in Sweden, acquired Mack and Renault in 2001.
The new work in Washington County comes two years after Volvo said it would lay off up to 600 employees, roughly one-third of its local work force due to a slumping market.
Perkins said at the time that "a massive pre-buy," just before tighter emissions standards, was expected to hurt 2007 sales.
Subsequent market fluctuations have further reduced the plant's work force to about 1,200 jobs. Some layoffs are seasonal and employees might be called back, Perkins said Friday.
The Volvo summary page says the company has had capacity issues with its foundry in Skvde, Sweden, and its machining operations in Skvde and Brazil.
The Washington County investment will "reduce our logistic costs in North America, provide a currency hedge, and increase the NAFTA content" of Volvo products, the sheet says. "NAFTA content" refers to North American Free Trade Agreement rules.
The summary page says Volvo is looking for a North America supplier for the blocks.
Perkins said some details of the machining won't be decided until the company agrees to a new labor contract.
He said a three-year contract expired Oct. 2, 2007, but employees still are working under those terms. Contract negotiations are expected to resume next month, he said.
Employees: 1,200 now
Investment: $50 million in a new engine block machining line at the plant north of Hagerstown
What it will mean: 50 new jobs