Illegal hands to the face?

I understand the "hands" rule, but is it illegal to use your forearm, or bicep, or shoulder against an opponent's face? For the one year I played in high school, I was an absolute monster - one, because of my size, and my brain, and two because of my using tactics that are reprehensible, yet legal. Coming off the snap (most of the time I was playing either O or D line, save for one game where I played linebacker, and all I was told to do that game was rush the QB no matter what) I immediately hammered the player opposite me with a forearm to the chin.

That initial hit I did every single play always rendered my blocker/attacker useless (and a few times, unconscious) and I was never called for an illegal hands to the face. Is that call made if it's not hands?

Mainly, if I someday coach football kids, should I not suggest that technique? I was never called for it, but that could just be bad refs. If someone played today as a pop-warner/high school/college player, would that be called every time?

When I played in high school, our coach taught it to us and then told us it was illegal. I'm not sure when it became so.