Go about 1/8" to 1/4" past the end of the crack and drill a 1/8" hole
This helps to arrest the crack getting bigger.
If you wash the crack really well, JB Weld will fill the crack reasonably well.
Just make sure the bolts on the cover plate are kept tight.
The crank will start weeping after a while, but I have managed to keep a couple of these owned by non - profit / charity clubs running like this.
Also check the oil EVERY time you use the mower.
OTOH I can now weld the cases , with oxy using a DHC 2000 low pressure gun and fine filler rod.
Electric welding does not work as well as you have to get the crack surgically clean & dry in order for the weld to work.
Unless you have a friend who welds, or the gear yourself, a short block will be a better and most likely cheaper if you want a permenent fix.
Products like Lumiweld and similar alloy "welding" rods ( they are actually solders ) can also do a reasonable fill if the crack is really really clean.
But again this is not structural and has little more strength than the JB weld but at least it will not leak.