Just to add a little to what the others have already said, some engines have such a precisely fitted rocker arm to pushrod end that even when the valve is open and things are under the extra pressure, you can still turn the pushrod with your fingers.
It might be notably harder to turn, but the point is that it can still be turned even while under pressure. That's why when setting lash on an adjustable valvetrain you use up-and-down motion rather than spin.
And regarding the ticking sound, how old is the engine and with how many miles? Might just be getting sticky in there. We haven't had a good "snake oil" discussion lately, so now might be a good time.
If your engine is older, or has perhaps not had good maintenance in the way of oil changes, or has run hot or used cheap oil, or has just sat around most of it's life, you might just have some gummed up lifters. In which case some oil additive designed to disolve the deposits might just work.
They're not the miracle cures they're made out to be, but they do have their place and can work. And at a few bucks a can, don't hurt to much to try even if they don't work in the end.
If you fee like it then, and are driving the Bronco regularly now, a can of additive that says "frees up sticky rings and quiets noisy lifters" (seems to be the way it's worded most of the time) would be a good thing to add and drive around a bit with.
If your oil is relatively fresh, just put it in and go. If you're about to change the oil, then wait until you do to add the cleaner.
In my case, the stuff worked great on my '71's engine. Did not fix it permanently, but got me another 30k miles out of it before I had to replace the lifters. Saved me some hassle and money and lungs, since at the same time it stopped smoking, quieted down nicely, and my oil consumption went from 1 quart per 500 miles to 1qt per 5,000 miles!
So yeah, it worked for me and I'm still a fan even though it hasn't worked in every case.
But it's worked enough times to make me a believer.
Paul
