Paccar’s MX stands out with unique design features.
Every trucker places a high value on torque and an engine’s ability to pull hills without needing to shift. Paccar’s new MX, which is close to full production at the company’s Columbus, Miss., manufacturing facility, has one unusual feature – fractured cap technology – that enhances this characteristic.
The process involves the splitting the main bearing mounts and connecting rods. When they are reassembled, the mating of their rough edges produces an alignment more precise and rigid than standard rods or main bearing mounts, which have smooth mating surfaces.
The perfect alignment makes it possible to tune the engine to produce a “wide horsepower range and longer torque and power curves for more efficient operation,” according to the company. The technology also provides “improved bearing clearance, higher strength joints, increased uptime, and longer service life.”
Paccar says the engine is the only one in the marketplace that uses compacted graphite iron in both the block and cylinder head: “CGI is lighter and stronger than traditional gray iron and offers weight-sensitive users excellent horsepower-to-weight ratio to optimize payload,” a company report says. “The distinctive MX crankshaft reduces weight and increases power for quicker acceleration and smoother overall operation.”
Up to 75 percent stronger than gray iron, CGI is “200 percent more resistant to thermal fatigue,” the company says. That property contributes to a projected “industry leading” service life of 1 million miles for 90 percent of the engines produced, says Preston Feight, chief engineer for Kenworth Truck Co. “Using CGI in the block and head reduces weight and provides for a very high-strength, reliable and quiet engine,” he says.
Another unusual aspect of the design is the single, in-block camshaft, which is driven from the flywheel end of the engine to minimize noise and vibration. This layout uses highly developed unit injector pumps, along with sophisticated electronic control valves on both the pumps themselves and the injectors they feed to coordinate fuel delivery.
“We can achieve 36,000 psi at the injector tip,” Paccar says, “which allows for excellent fuel atomization and combustion, delivering superior fuel economy and low emissions.” Also, the fuel galleries are integrated into the cylinder head to reduce leaks, and improve reliability.
The camshaft operates the unit injector pumps, the four valves per cylinder, and the integral, camshaft-operated engine brake, which is rated at 465 hp, and allows a low total engine height for easier fit under hoods designed for ideal aerodynamics.
The engine’s integrated lubrication module combines filters, a thermostat and an oil cooler joined directly to the engine without external lines “to maintain oil quality and extend service intervals,” Paccar says. “The module includes an easy-to-access, cartridge-style oil filter to make service visits quicker and cheaper.”
The MX also features a fully encapsulated wiring harness mounted directly to the block, said to “protect wiring from the elements and remove stress from connectors” and result in optimum dependability in the electrical system.
“The oil filter module, which consists of a cartridge-style filter in combination with a centrifugal element, offers a maintenance interval of 40,000 miles,” Feight says. “The module is located forward on the passenger side of the engine for easy access during service. When the cover is loosened, oil in the filter module drains back into the oil pan, which significantly reduces the clean-up normally associated with an oil change. The fuel filters are located rearward on the driver’s side of the truck and are also well-placed for ease of service.”