The reason told to me for why you want non-detergent
oil, by one of the old time engine builders who got me started in engines, was that the detergent
oil would pick up all the "junk" in your motor left there from the build, and suspend it in the
oil, then circulate that crud through the motor. That lint, assembly lube, dust, etc, could then have the opportunity to clog the filter, then the oil would get forced through the bypass, unfiltered. Better to run the non-detergent oil initially, it wasn't as good at picking up the "junk" so the oil filter wouldn't bet clogged before you get the cam broken in, when you should change the oil anyway, and repeat the process. Better to catch some of the junk in the first filter, some in the second filter, than to get it all into the first filter and clog it up. That was many years ago, the old timer is long dead, but what he told me has stayed. Due to the non-detergent oil being a special order item, the shop I worked in never suscribed to that practice, just use the same valvoline oil as always for new motors. I did do it on my own motor though, and no noticable negative effects were seen.
quote lubricon:
You may be able to buy a non-detergent motor oil from some backyard blender, but not from ANY major supplier of engine oils today. The spec has been obsolete for years and you should never use a non-derterget oil and any engine for any reason other than to screw it up big time. That includes "break in" or whatever.
Now we know that you can get it from valvoline and castrol. But how will it "screw up a motor big time"?