[blykins]

Use a longer wrench. Just break loose the nut. The hex thing in the middle is the adjuster...it's what contacts the pushrod cup. That's how you adjust your lash. You run that middle hex adjuster down till you get the lash you want, then you tighten the nut with the wrench.

Just use a longer wrench...or take a dead blow and tap the end of the wrench that's on it now.