Application Xtra

Propulsion system gets its motor bearings

• corrosion resistance
• environmentally friendly

FourStroke motors are emerging as the sport marine standard, based on a combination of EPA regulations and consumer demand. A FourStroke motor has entirely separate systems for exhaust and intake valves, making it emissions safe and environmentally friendly. The Verado motor is purported to be the first FourStroke outboard to deliver 275 hp. Manufactured by Mercury Marine, Verado has complete steering and control systems and features a supercharger, providing a combination of packaging, throttle response and thermodynamics management. The supercharger system also enables the manufacturer to use a smaller-displacement block.

Much of the motor’s four years of development was spent ensuring its superior performance to a 2-stroke of the same horsepower. When designing the new motor, engineers kept three things in mind: power, reliability and modern technology. Historically, the boat motor industry employed metal bearings with a nylon liner or simply mated aluminum on stainless steel with no bearing at all. Other times, engineers used aluminum-backed, fiber-reinforced bearings, with a press-fit into other pivot points. These solutions required grease lubrication, which was quickly washed away by the water, resulting in water contamination, possibly harming local wildlife, as well as additional maintenance. As a result, Mercury Marine engineers also were charged with the task of making the motor as maintenance-free as possible.

The engineers decided to seek bearing alternatives and discovered maintenance-free iglide plastic bearings from igus inc. Design engineer Jeremy Alby worked closely with the bearing company to find a solution. “Igus offers such a huge variety of engineered materials, it was just a matter of determining which one was appropriate for each aspect of the application. Igus worked with us using its in-depth test data and predictability methods to find the exact bearing solutions we needed. We found a number of materials that work in different parts of the motor.”

The motor uses more than 10 iglide bearings, primarily in the steering component and transom assembly, which enables tilt and trim of the motor. The iglide G300 is used in these oscillating pivot joints because of its low-cost and ability to withstand the harsh mechanical conditions.

Verado and all its components also need to withstand the rigors of the sea. The bearings are submerged in highly corrosive salt water, which can damage the bearing and rod over time. The plastic bearings will not corrode and seize and can withstand high impact and high loads, up to 10,000 psi.

Mercury Marine chose the iglide D bearing for the steering component because it ensures smooth motion with its low coefficient of friction, both static and dynamic. It also has a low water-absorption rate, reducing the chances that the bearings will swell, affecting engine feel, which is crucial for boat control, especially at high speeds.

Another factor in the decision to choose iglide for Verado was the fact that the parts could be custom-tooled. “More than half of the bearings on this motor require custom tooling,” says Alby. “The ability for these bearings to be slightly press fit or slip fit aided manufacturing and also provided greater overall surface area.”

The engine is a highly reliable, with more than 25,000 hours of testing—both in the lab and on the water. “Igus has been testing its bearings since day one and continually compiling that information into a comprehensive database,” said Tom Miller, national bearings business unit manager for igus. “With that test data, we are able to predict accurately the lifespan and degree of wear of an iglide bearing under any circumstances.”

Mercury Marine is set to produce 20,000 mature volumes of Verado beginning this year. It has won several design awards, including those from the Industrial Designers Society of America and the Structural Plastics Conference.

igus Inc., East Providence, RI
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