Motorcycle Rocker Box

What is a Rocker Box?  Sorry, it has nothing to do with Rock and Roll unless you are jamming away in your garage while wrenching.

Honestly, it is kind of a funny term. 

My wife laughs at me because I tell her that I am going to teach our puppy to speak, and that Gracie’s first words will be Pushrod or Rocker Box.  Sometimes I think about the terminology that goes along with DIY wrenching on motorcycles, and it cracks me up.  Anyways….

Ultimately, I want to do a detailed post about checking rocker arm specifications and reconditioning, but for today this post is purely definitional since I am sure there are some people out there asking themselves, “What is a Rocker Box?”

What is a Rocker Box?

Engines have cylinders where pistons go up and down, but we must never forget that the primary motion generated by exploding gasoline in a motorcycle engine is circular. 

Flywheels spin, and that power needs to be transferred to the back wheel via the transmission and to the valves via a camshaft and pushrods. 

The circular motion must result in the opening and closing of valves, and we can thank the combination of push rods and rocker arms for this transition.

Essentially, as the flywheels spin, so does the camshaft, which pushes on the tappets (a story for another day), which lift and lower the pushrods.  What is on the other end of the pushrods?

You guessed it.  Rocker arms. 

But I didn’t really answer the question of what is a rocker box. 

On a Harley, the rocker box is the enclosure that sits on top of the valve head. 

It is literally the box the rocker arms and rocker shafts live in. 

Rocker arms are “flipped” sort of back and forth by the top of the pushrod. 

How Motorcycle Engine Rocker Arms Work

When up, the other end is down (think like a seesaw), and the other end is pushing down on the top of the valve spring.  And just like that, the valve is open. 

Flywheels continue to spin, pushrod lowers, rocker arm lets pressure off the top of the valve springs and the valve closes.

Let’s review. 

Engine spins, pushrods go up and down, and rocker arms push down on top of and release pressure from off of the valve springs. 

Without this combination of camshaft, pushrod, and rocker arms, valves would not open and close – a much needed part of the overall engine combustion cycle unless you are on one of those fun two-strokes.

That’s it.  Hope you learned something!