Doing it on a running engine is super easy with the valve tool. Get the right feeler and try to insert it on the stem. If its to tight the feeler will not slip in, if its to loose it will.
With the feeler in on the stem you are at zero lash.. not a huge deal, so just use the handy valve tool to both adjust the lash so the feeler goes in freely and then tighten the bolt.
The tools come up on ebay for about $30. Some are double ended, others just single ended.
