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Casting Porosity: Harley Davidson Cam Plates

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No doubt the Harley Davidson motorcycle is an iconic product, but for years they have had notoriously unreliable cam plates.  This critical component suffers in part because of the nature of its construction.

Stock cam plates on Harleys are die-cast parts, and like all cast, parts are likely to have some degree of porosity.  Porosity, simply voids or holes in the casting, if excessive, can cause serious reliability problems. If kept to a minimum, casting can result in highly reliable, low-cost components.   Two common types of defects, gas porosity and shrinkage porosity, result from a variety of errors in the process.  The weakness these defects cause is exacerbated by heat cycling as experience by a cam plate.  Inspection of parts throughout the manufacturing process can identify parts suffering from excess porosity, and also inform adjustments to the manufacturing process itself that can improve component consistency and yield.

X-ray inspection is an ideal method of evaluating cast parts for porosity, as well as for inclusions and other defects.  Using our Truview™ X-ray inspection system, we were able to easily image both an OE (cast) Harley cam plate as well as a CNC machined aftermarket replacement.  There is a striking difference between the two, and the voids in the OE cam plate are easily detected.  If examining such a product during production, image analysis could rapidly identify the percentage of voiding for each component and determine if the porosity exceeds acceptable standards.  Likewise, software tools could call out voids in regions of the cam plate that might be more likely to induce failures.

X-ray images of the original (OEM) part from Harley Davidson using a casting manufacturing process (left). The aftermarket billet aluminum machined part is on the right. Note the significant difference of porosity between the two cam plates. 

It’s easy to see why so many of the providers of aftermarket solutions machine their cam plates from billet aluminum.   Parts machined from solid stock don’t suffer from the inconsistencies sometimes found in poorly cast parts.  The consistency is apparent in comparative X-ray images.

Cast parts, such as the Harley Davidson cam plate, can be highly reliable as well as relatively inexpensive to produce.  That said, they do require a high degree of quality control to ensure proper performance.  Non-destructive testing and evaluation using X-ray inspection can make a significant contribution to the quality improvement and reliability of such castings.  For additional information or questions about casting inspection, please feel free to contact us.



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