I had an unfortunate episode where a single flywheel engine ran a very brief time (less than a minute) and the flywheel came loose on the tapered crank and keyway. It destroyed the crankshaft, splitting it deeply and peeling it apart at the key from the intense hammering of the single cylinder design. The tapered hole in the cast iron flywheel was pretty gouged up but actually survived and without any machining was able to be put on a new crank pin with new key and has been just fine. I put on a liberal coating of blue locktite in this joint for insurance. I hope I never have to pull this apart.
In the case of this Whitte there is a second flywheel on the crank at the other end which would have radically reduced the hammering shock that my engine suffered, still, there could be crankshaft damage associated with the key slot.