Usually they do not damage the bore. Really the only way that happens is with low oil and excess heat.
Ive had one here that was low on oil and grabbed on the bottom of the crank. Ive had another here that was run low on oil and it grabbed on the top of the crank under the flywheel. Id say thats what happened in this instance.
Neither had bad bore damage.
If you had bore damage you would have smoke, either burning it or from crankase breathing.
My mate ran his low on oil and he got it freed up and it ran Ok.
Has the back of the crank case got vertical ribs cast into it???
Not sure about draining it, if you never check the oil it is not hard for it to get down that low. Probably threw it out because it seized.
