I remember a comment my machine shop manager said when I was discussing bearings with him on my 331 build. He said " all bearings are not created equal". When I asked he said he had found minute differences from one type or one manufacturer to another. I was only familiar with Clevite and my stroker crank mentioned running a specific Clevite bearing so I got all Clevite.
So, apparently there can be a run out issue with a cam. Any more than one thousandth and its no good. Even with a thousandth run out could that put put the journal tolerance too tight and the cam bearing ID's would then have to be reamed?
Roller cams have prompted bearing manufacturers to switch to an aluminium alloy bearing to handle the added stress, load and heat the roller cam can produce. These are less forgiving than the old babbit type bearings.
The cam journal tolerance as I read it is 2 thousandths for a stock build and 3 to 4 for a higher performance build. Since you can stack up tolerance issues from the cam bearing ID, block distortion and the cam journal run out it looks like it can be pretty easy to go too tight.
You are apparently supposed to torque down the main caps before installing the cam bearings which can create some level of distortion that can affect the cam bearing tolerances.
This is all stuff I have never even thought about. I don't have the cam bearing tool and haven't installed them myself in my few engine builds. I have always had to take a block to the shop for other things anyway so I have always had them install the cam bearings.
You may be dealing with one or the other or both a cam journal ID thing and a cam run out thing, the 2 of which created a too tight situation on the bearings.
All great points. I am going to measure/mic a bunch of stuff and see if anything jumps out at me. As for the cam bearings, I did not torque the main caps before installing the cam bearings. I read do it/don't do it, and decided to not. Again maybe a mistake. I did test the cam after I intalled the crank and torques all and it still spun freely. Freely as in by hand but all the assembly lube in there it did have some resistance, but it felt "good" to me, easy to turn.