Retainer to guide clearance was checked by the machine shop, as well as the springs, and I used an adjustable pushrod to check the length. However, I didn't use softer springs for the break in, just the same springs as I have been running. Maybe that was it?
I did use lots of assembly lube on lifters and cam.
Every lifter dropped in easily but snug, and I did ensure that they spun in the bores. The machine shop also checked the bores when they had the heads.
Now I'm wondering about the springs. I did read that some folks use lighter springs for break in, but for a reason I can't recall, I opted not to use them.
