Solid lifter cams no matter what they were in, I always set cold. Hydraulic lifter cams I used to adjust the lash to where the rocker could be moved a tic side to side cold at TDC on each cylinder, (valves closed) then while the engine was running at normal operating temp, do any re-adjusting that might be needed especially with the old TRW anti-pump up lifters. That's how I was taught as a young lad in the early 60's...

Steve@B&B

Being old, I remember guys adjusting valves with engines running......very common back in the "ol days". Some of the old timers made up valve covers with the tops cut out to alleviate "some" of the mess. Go-NoGo feeler gauges made the job a little easier and quicker.

I do remember that many years ago as a much younger lad, I took it upon myself to give the old WD45 a tune-up as a surprise for my Dad. I bought all of the ignition components myself as well as a carb rebuild kit. Cleaned the carb and installed all the new components as well as installed all the new ignition parts without any trouble whatsoever. Figured while I was at it, I'd pull the valve cover quick to check/adjust the valves if need be. Silly boy I was, I went by the book whatever it did say. They were close but not what the book said so I adjusted them. Got her buttoned back up, fired up, and carb adjusted before I drove her to where Dad was working. He took notice as my work had made a difference-she was definitely running better. As we discussed all that I had done, he was noticeably impressed and dare I say, somewhat proud until I mentioned that I had been into the valves. He asked me point blank what the settings were to which I replied that I had used the manual. At this point, he instructed me to walk back to get the necessary tools to pull the valve cover and do it again right where she sat. As we opened her back up, he did explain to me why we were doing so. The story went that about 25 years prior to this when she had her last rebuild, the local AC mechanic re-built her engine to maximize hp output per Dad's request. At that time, she was still the big tractor on the farm. The XT wouldn't show up for another 2-3 years. Dad never really bothered to get the details on just what was done because he was so ecstatic when they told him that she dynoed out at 56 hp at the pto when all was said and done. This elation was short lived, however, when she quickly developed a habit of burning valves. After a little trial and error costing some valves, they discovered that the sweet spot seemed to be a setting of 0.013" across all the valves and she finally stopped burning them. The whole time I was growing up, I don't recall her ever being down or her engine worked on again. We set all the valves back to 0.013" that day and those valves from the late 60s are still in there to this day.

That was cold which was 1 reason why he had me walk back to get the tools. Like others have commented, Dad always thought it was silly to specify a hot setting when adjustments were a lot easier and way less messy when it wasn't running-LOL.