Split lock washers have long been considered marginal at best for securing a robust threaded joint. When a split lockwasher is fully compressed flat it has no retaining "bite" at the split and actually becomes a flat washer with a crack. The tensile spring force created by the compression of the washer contributes only around 10% of the torque preload. The rest is covered by bolt stretch.
For the washer to bite and provide a lock the bolt will need to back off a bit but then the clamp load is lessened and you're joint has failed.
The best lockwasher for high preloads is a conical washer with serrated faces.
For the most part though using the tensile bolt stretch to clamp the load is the best approach and is the norm.
