Q. What happens if I use 10w-40 oil in Interceptor 650? Will it be okay?

The difference between 10w40 and 10w50 is how thin the oil gets when it's hot, 10w50 oil won't thin out as quickly as 10w40 when oil temperature goes up, but it also might be too thick during regular running in cold temperatures.

Company recommends 10W50, which is freely available. Don't use different grades. It can s***w up your engine.