There is some dispute about that, Some people think it was an oil slinging problem. Junkers engines had off set superchargers and yet used the same compression ratio on both sides. Some Russian engines may have used different compression ratios on different banks. Some engines may have been different but the difference not enough to really talk about? A number of engines had different stokes on each bank (articulated rods) and even using different pistons it is hard to get exactly the same compression ratio.