My old 216's valves chattered even after setting them to spec. Didn't matter hot or cold they'd let me know the engine was doing it's thing.
Saw a post somewhere, here no doubt, where someone pointed out how the rocker tips would wear a trough where they contacted the valve stems and this trough could be a couple thousands or more deep. What would happen when setting your valve clearance was the feeler gauge was reading the surface that didn't contact the stems and not where it was wore in. So basically one would be adding a couple more thousands or more of clearance to the settings.
To correct the issue, take both rocker shafts off and take a couple pic's of how the rockers line up then remove the rockers and dress the tips up to where the surface is smooth and even, retaining the radius while doing so, do not make the tip perfectly flat or you'll never get them quiet.
I did this and my 216 never ran quieter.
Another poster that I don't recall either, LOL, said he ground down a set of feeler gauges so they would fit into the wore spot to measure the actual clearance. I'd say thats doable too.
This could be your problem.
Good luck
Dave
