This is what the factory tool looks like. Centre piece fits on the square bit, other piece on the lock nut. So you can hold the adjuster in place while you tighten the nut. They make longer feeler gauges with a bend on the end so you can get in there. If there is any wear or pitting on the end of the valve stem, it’s better to adjust them without the feeler gauge. If the stem is worn, the.gauge slides over top of pitting and gives you a false reading. You can just “lightly” snug down the adjuster to take out any clearance and then back it off a 1/4 turn or whatever works out to .002
Might want to sort out your charging system first.
Might want to sort out your charging system first.

