The phrase "primary engines" is correct and usable in written English.
It is typically used to refer to the main or most important engines of a vehicle or machine. Here is an example sentence: "The airplane's primary engines failed mid-flight, causing the pilot to make an emergency landing."
The result is that the Karzai government has become one of the primary engines driving people to the Taliban.
These losses transformed local housing declines into a global crisis and, along with the breathtaking fall in stock prices, have remained the primary engines of disaster.
According to private-sector readings, which aren't filtered through China's state apparatus, manufacturing and real estate, the two primary engines of the Chinese miracle, are both slumping.
The primary engines of Goldman's recent success have been its sales and trading of bonds and commodities, Mr. Blankfein's area of expertise.
The staffing problems arise as the government has invested hundreds of billions of dollars into the companies and has expanded their mission to be the primary engines to pull the housing market out of the doldrums.
But time appears to have modulated Tatel's view that courts should be the primary engines of social change; he now seems to feel that courts can enforce constitutional rights but should not impose heavy-handed remedies in an effort to remake society.
But I see research as the primary engine.
Mr. Protti said that the American market was "the primary engine of growth" for Canadian banks.
Cheap fossil fuels were the primary engine that grew our society over the last two centuries.
"Exploration and production is the primary engine of income growth," Mr. Hess said.
Clearly, nostalgia for Iranian tradition was not the primary engine driving Saqqakhaneh art.
