What It Looks Like

Aircraft engines produce horsepower, but in so doing they also generate exhaust gases and vibration. Exhaust manifolds and mufflers deal with the former, while elastomeric isolators handle the latter.

Engine isolation mounts often are called "Lord mounts" because the major supplier is Lord Corp. You may also hear them referred to as "engine mounts." In fact, the engine mount is the metal cage or framework to which the engine is bolted through an intermediary - the isolation mounts.

Isolation mounts are rubber discs that absorb engine vibration, which otherwise would be transmitted directly to the rigid engine mount and then throughout the airframe structure, including the passenger cabin. One can only imagine the noise and vibration in an airplane without engine isolation mounts.

The isolation mounts in the accompanying photos were removed when the engine was overhauled, which is what Lord Corp. recommends. Over time, isolation mounts distort as a result of constant compression or tension (depending on the location of the isolator) from the weight of the engine. High temperatures inside the cowling also can accelerate deterioration, as can excessive fluid - oil, fuel, and hydraulic fluid.

Engine isolation mounts are not easily examined during a preflight inspection because most are hidden deep within the cowl. However, signs of worn mounts include excessive swelling of the rubber doughnuts; cracks deeper than 0.125 inches; or a hard, shiny surface with crazing, which is a sign of prolonged exposure to high temperatures. A prop spinner that sags noticeably relative to the nose cowl also may be a sign of tired isolation mounts.