Vector3 script not working?

--I made A script that stretches my arm.But when i press e nothing happens I need the vector 3 y value to expand by 4 but its not working.
Char = game.Players.LocalPlayer
mouse = Char:GetMouse()

mouse.KeyDown:connect(function(key)
	key = key:lower()
	if key == "e" then
		RS = Char.Character.Torso["Right Shoulder"]
		RS.C0 = RS.C0 *CFrame.Angles(0,0,-32)
		RA = Char.Character["Right Arm"]
		RS = RA.Size
		RS = RS + Vector3.new(0,4,0)
	end
end)

Your script is mainly not working because you are trying to change the size of a Motor6D which you cannot do. I have edited your code and got it to work a bit except the arm falls off when you try to change the size. I do not know why (probably because it's breaking the Motor6D which welds the parts together) but here you go.

Your Code Fixed

 Char = game.Players.LocalPlayer
mouse = Char:GetMouse()

mouse.KeyDown:connect(function(key)
    key = key:lower()
    if key == "e" then
	print('0')
        RS = Char.Character.Torso["Right Shoulder"]
        RS.C0 = RS.C0 *CFrame.Angles(0,0,-32)
        RA = Char.Character["Right Arm"]
        RA.Size = RA.Size
        RA = RA.Size + Vector3.new(0,4,0)
    end
end)

Study how characters work and try to fix that little problem if you really want to fix it. Or consider another method.

Hope this helped!