I've only recently noticed that inside cylinder six coupled locomotives have the wheel balance weights in the 'wrong' place. I don't know how I missed it all these years. With an outside cylinder locomotive, the connecting rod big end is always concentric with the coupling rod bearing, so the balance weight is opposite. I understand that with inside cylinders, there is no such restriction and the designer can put the big ends anywhere on the crankshaft/axle in relation to the coupling rods, subject to each pair of cranks and coupling rods being quartered to each other. So why are they designed the way they are? If say, when all viewed from the left, the left hand coupling rod is at 12 o'clock and the right hand coupling rod is at 3 o'clock, why not put the left hand connecting rod at 6 o'clock and the right hand connecting rod at 9 o'clock? It seems to me that this would improve static balance, and with weights added to the wheels and crankshaft/axle opposite each bearing, the dynamic balance would improve and hammer blow would be reduced. What have I missed? I realise this could be a complex subject. I'd be happy with a link to an article or book rather than expecting someone to type out a long explanation here.