Is there a relation between spun bearing and a cam installed...
The new cam'd motor sees higher RPM than it did with the stock cam. The user is revving more and higher RPM. As RPM increases blowby and ring wear increase. This can allow your oil level to drop off. Once you spin your motor to 6K+ RPM with low oil, bye bye bearing.
Ben T.
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I'm assuming the installer of the 2nd cam grooved up the bearings rather nicely with the install. Sounds like your problem may be similar... it's not uncommon. 

