PISTONS UNDER MICROSCOPE
When buying pistons, it’s easy to run into a fake - you won’t carry out an examination in a store. We sent the purchased parts to the laboratory.
The object of the study was pistons for the widespread KAMAZ 740 series diesel engine. They are produced by more than a dozen enterprises in Russia, Ukraine, and Kazakhstan. The leader is the Kostroma Motordetal plant; he owns 30% of the market. Recently, Kostroma won a tender for the supply of products for the defense industry, and the military, as you know, the most picky buyers. It is not surprising that in shops pistons with a ladder and a dot in a circle (Motordetali logo) are in high demand. But the "left" producers are not asleep - their factories in our "market" conditions are growing by leaps and bounds.
In several stores we bought three sets of pistons. At all - a familiar logo. However, an attentive buyer will immediately notice that on one of the sets in the “ladder” there are four “steps”, while on the original brand there are only three. Looking ahead, we confirm the conjecture - this casting, like the processing, has nothing to do with Motordetali. The “pedigree” of another set is interesting (casting index 7405-1004015-42): casting is native, but the part was processed outside the factory walls. Nesunam everywhere we have a road? Only the third set turned out to be real. The research results are summarized in table.
Conclusion: the pistons from kits 1 and 2 do not meet the technical requirements. Due to the small width of the groove under the oil scraper ring, it can occur and a large oil consumption for waste. The roughness of the hole for the piston pin is also large (especially for kit 1) - when the hole is worn, the piston stroke will increase and its encounter with valves is not ruled out. This is facilitated by the increased compression height - it is not sustained in both sets, as well as the depth of the valve seats. When installing the pistons of set 2 in the engine, “sticking” and jamming of the engine are possible due to their increased diameter and vertical profile distortions. In addition, metallographic studies showed that the pistons of kit 1 are made of an alloy with a lower silicon content than provided by the design documentation - their strength is in doubt.
How not to make a mistake when choosing? First of all, carefully consider the casting. The influx of metal shells on the surface should alert. The metal of Kostroma pistons has a grayish tint, while fakes often sparkle like a Christmas tree toy. Coarse marks from the cutter, large feed (large grooves) are also a sign of fake. And, of course, do not “look at the elephant” - the differences in marking and logo.
The original brand "ladder" with a dot in a circle.