[Barry_R]

As far as I know every popular car engine sold today has gone to roller cams for improved efficiency and mileage.

Waaaaay back in the 90s (remember those?) GM had a huge spate of defective cam cores and subsequent failures. In the early 2000s Chrysler had an equally large scale problem with cam failure on 2.5L engines even though they were rollers.

It only seems simple - but a surface hardness test will not give an adequate measure of hardness depth. A core that does not have a deep enough hardness layer - either from inadquate processing or incorrect core grinding or selection - will suffer premature wear and eventual failure as the underlying material deforms and fails.

The only way to check for this is destructive testing of a statistically significant number of finished product samples. That is how the OEMs do it, but its pretty tough for a lower volume, high sku count aftermarket supplier to follow suit. Its common for them to run spot checks on cut cores. Even that may not find a casting where a single burner went out during flame hardening...

Stuff happens, and it ill happen most often to the company that sells the highest volume of product.