McFarlane Aviation now manufactures improved FAA-PMA carburetor heat box repair parts for most single engine Cessna aircraft. The line of new products includes bearing housing assemblies, butterfly shafts, arms, monel rivets, and roll pins. All of the high quality parts are priced lower and McFarlane makes discontinued parts available.
McFarlane has developed an improved bearing system for the Cessna single engine carburetor heat box. The new McFarlane bearing housing design incorporates a special elastomer bearing that replaces the original needle bearing. This unique design absorbs normal heat box shaft and butterfly vibrations that occur during flight. Reducing the effects of vibration drastically increases the heat box components service life with a net savings in maintenance cost.
The carburetor heat box suffer more from engine vibration than other parts of the engine installation due to the distance of its location from the center of the engine. Engine vibrations, which are small back and forth movements of the engine about a point of rotation in the engine, become larger and more severe as the distance increases from the center of these movements. A fraction of an inch of engine movement near the center of the engine could result in over an inch of movement in an attached component that is located a considerable distance from the center of the engine. This phenomenon can be visualized by imagining what would happen if a five foot broom handle was solidly attached to an idling aircraft engine. The far end of this broom handle would oscillate wildly back and forth as the engine moved slightly. This is similar to what is happening to the carburetor heat box. Normal engine vibrations are amplified by the distance (arm) from the center of the engine.
Ordinary needle bearings are not well suited for this high vibration environment as they concentrate the energy of vibration movement to the very small area where the needles contact the heat box butterfly shaft. This concentrated kinetic energy results in metal loss and grooves being worn into the shaft with eventual failure of the bearing system. Needle bearing failure can lead to ingestion of loose needles into the engine induction system and cylinders.
The McFarlane elastomer bearing is assembled with tension between the mating surfaces. This tension prevents mirco-movement and its related metal erosion. The McFarlane bearings contact area that transfers vibration motion from the heat box to the butterfly shaft is hundreds of times greater than that of the original needle bearing. This large surface effectively prevents localized metal erosion. Extensive cycle testing (over 700,000 operating cycles) has proven that this new bearing is extremely rugged and wear resistant in high temperature and fuel environments.