Metal timing chains are widely used by most carmakers and engine manufacturers. But as demands for lower weights, costs, and noise continue, automotive engineers are turning to plastics for components in the timing systems, such as the chain tensioner.
The Porsche Cayenne SUV, for example, uses a two-part tensioner made of two grades of Stanyl from DSM Engineering Plastics, Evansville, Ind. (www.dsmep.com), to replace what was once an all-aluminum component. Stanyl TW314 is a PA46 with good wear characteristics and oil resistance, and can withstand engine operating temperatures of 140°C. It's used for the top layer that presses on the timing chain. It is nonabrasive, so friction drops and chain life lengthens. Stanyl TW241f10, a 50% glass-filled PA46, is strong enough to be used for the base of the tensioner. It resists oil and fatigue, has a high modulus and stiffness, and low creep at high temperatures.
The stiff tensioner base is molded in its final shape, complete with the proper curvature for handling the chain. All mounting and pivot points, as well as reinforcing ribs, are precisely located for fast, simple assembly. The top layer comes from its mold with a smooth finish, complete with guides for the chain.