This is a weight advantage over the I4 engine , which will need a balance shaft .
The second advantage is that the W4 lacks the need for a balance shaft ; it will run smoothly if the two crankshafts rotate in opposite directions .
This is a W4   over the I4 engine , which will need a balance shaft .
The second advantage is that the W4 lacks the need for a balance shaft ; it will run smoothly if the two crankshafts rotate in opposite directions .