We have a 65 Belvedere with a never been apart 225.
I decided it's due for a lash adjustment.
With everything hot I set the intakes to tight on my .010 and easily slip my .009" in there. Exhaust same, 0.020 with some drag and my .019 easily slipped through. Most only needed to be tighten up very slightly like 1/16 of a turn. Worst ones where only 1/8".
Idle quaility in gear is not as smooth as before. Not shaking you out of the car or anything but you could feel it slightly twitching.
Before lash adjustment it was dead smooth, like our 3.5L fuel injected LHS.
I ripped off the valve cover to recheck my work. After double checking my work I decided to try a looser adjustment.
My .010 loose drag and my 0.20 on ex, loose drag.
No surprise, idle was slightly smoother but not as smooth as before.

My Dad and I just adjusted the valves on my '61 Valiant, 170 1V, and afterwards, it is dead smooth.

I swear that, in gear, warmed up, it's smoother than my Mom's new Toyota.

When we adjusted the valves, 2 of the exhaust valves were way loose, making the motor skip around a little at idle and tick like crazy.

Nick,
The new guy to slants...

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I would go looser on the exhaust valves, try them at .022 to see if you can get that dead smooth idle back without any loud "ticking".

It is not uncommon to have to "fudge" a little on the lash adjustment clearances to get the best performance / idle quality, especially on high mileage engines. This is why I like doing valve lash adjustments with the engine running, doing so will give you some "clues" as to what the engine likes.
DD

I was thinking of trying that. Initially I was going to try to loosen the intake since it's the tighter of the 2 valves.
Why do you suggest starting with the ex side?

The exhaust valves see a wider range in temperature and run much hotter, they expand & "grow" more.

The exhaust valve guide and seat also sees the most wear so on a well worn engine, you may need some additional lash clearance to compensate for that.

I have found that a tight exhaust valve(s) will cause rough idle sooner then a tight intake valve(s).
DD

My Dart Idles really roughly as of late. The Idle when cold is fine, but when it gets warmed up then it becomes very rough. I am pretty certain that mine's just bad carb adjustment (an old 1920).

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yeah, adjust 'em hot and running, listen to the motor and yer able to get 'em perfect

when i tuned and adjusted the valves on mine, I swear it runs as smooth as it did when it had 40k on the odometer. Shes just over 280k as of right now. /6's are bad about being stereo typed and sounding really bad or idling rough, ( by non-slanters). I'm proud of the way they are super smooth when adjusted properly.