I have given up on Delta cams after losing two forged steel cams and wiping out chilled iron lifters. Even following all the warnings about ZDDP, using Brad Penn break in oil, etc.
After the last tear down I took the cam to Oregon Cam Grinders and they evaluated Delta's work and said that the lobes of the cam were not appropriate for the NOS lifters I had purchased. (I had sent the lifters with the cams to Delta on both occasion).
Oregon Cam Grinders researched my cam, lifters, performance grind options and prepped the lifters, ground the cam and it went through break in perfectly as well as goes for several thousand miles without needing adjustment and the lifters now spin reliably and run far quieter.
This article is worth reading on this topic as well.
http://www.enginebuildermag.com/2009/04/flat-or-tapered-cams-and-flat-or-crowned-lifters/
