I have a Suntour BB with Suntour Sprint cranks.
Just got a Shimano 600 Crank, (I wanted longer arms).
They are both square taper but the Suntour cranks go about 7/8 of the way on the spindle and then get tightened.
The Shimano crank goes almost all the way onto the spindle to the BB shell.
I am guessing the BB is not the correct taper for the Shimano crank since if tightened it would be against the BB shell.