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"Will-Fit" Compressor Connecting Rods Fail Well Before Thermo King Rods
After receipt of numerous field reports pertaining to the failure of connecting rods being used as replacements in Thermo King 426, X426 and X430 compressors, laboratory analyses were conducted on three commonly available "will-fits". The analysis revealed several dimensional characteristics that were sub-standard and inadequate for Thermo King compressor applications. The inferiority and inadequacy of the "will-fit" rods were further revealed via an accelerated tension/compression cyclical-loading fatigue test. The rods were tested under identical conditions (load and cycle rate) until failure occurred. The "will-fit" rods failed well before the Thermo King rod.
KEY EVALUATION POINTS:
Dimensional Analysis — Dimensional discrepancies were found in 23 critical measurements including: pin bore, crank bore and parallelism. Rods that are too short will result in reduced capacity; if too long they'll interfere with the valve plate causing wear and eventual breakdown. Crankshaft bores that are too large can result in accelerated wear and reduced oil pressure. Lack of parallelism causes reduced lubrication and excessive wear.
Material Analysis — The "will-fit" rods were forged from a common carbon steel, which is typically chosen for its low cost and ease of machining. Thermo King rods are forged from an alloy steel, chosen for its superior strength and mechanical properties.
Microstructure Analysis — The "will-fit" rods shoed a course grained, pearlite microstructure, which gives very poor fatigue life. The same analysis of Thermo King rods reveals a fine grained, tempered, martensite microstructure, which insures a far longer fatigue life.
Surface Analysis — Embedded forging scale and decarburization was found on the surface of the "will-fit" rods. These imperfections will cause stress concentration areas, which will reduce the fatigue life of the rod. Thermo King rods are cleaned to remove forging scale and decarburization.
CONCLUSION
All connecting rods are not created equal. Just because it "will-fit" doesn't make it the right fit. Only by insisting on genuine Thermo King connecting rods are you assured of the right fit!
For more information,
contact your local dealer.
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