Scripting a object to rotate to the sides on the x cordinate

Hi I am having some difficulty figuring out how to set this up. I was using translate.rotation to write these first code examples.

transform.Rotate(Mathf.PingPong(Time.time, 3), 0.0f,0.0f);

After I wrote that I tired a few different setups having but when i get the object to rotate off the other base object it goes a full 360 without stopping.(sparing bag for a gym setup)

transform.Rotate(90.0f * Time.deltaTime 0.0f, 0.0f );

Any thoughts on how I can fix the full 360 rotation to where it rotates a selected amount on the x.