You made two statements, the exh. is not leaking, and the lifters "checked out". The two most likely culprits for ticking after a temp. change. I well know how difficult it can be
to find a small exh. leak when access is restricted, I use a piece of steel brake line w/a length of hose attached, hose to the ear and probe w/the line. If a lifter is mucking up
when it heats up, it can be hard to just "check", unless you run w/the valve cover off & check each valve & related one at a time. Put a stethoscope or long screwdriver on the
head as close to ea. valve one by one. Are the rockers the same ratio? any chance a pushrod is clippin' the block/head at a tite spot? Sometimes I just hold a rag and apply some
pressure on each rocker one by one and listen for a change. If it is not a singular tick, and is more of the "ratchet" chicka-chicka type, the piston could've suffered some type
of failure/damage. Hope this is helpful, good luck!
