Hydraulic lifter bleed down. Bad Hydraulic Lifters
352ci Ford in my 1966 F-100 shortbed. Just finished installing a new cam and lifters. Even needed new pushrods to get the preload correct. After all that, when the engine would warm up I'd get a pretty serious tick coming from one or two suspect lifters. Here's what I found in my diagnosis.
Rebuilding Hydraulic Lifters
This video shows the disassembly, cleaning, and rebuilding of hydraulic
valve lifters. These belong to a VW 16V head but many are similar. A couple
of these could be compressed by hand when they came out of the head. I
decided to rebuild all of them. This takes a long time so you might want to
consider just buying new ones, but if you have patience and don't mind the
work, it's very rewarding.