Re: what are these engines made of?
Something to keep in mind here. That 'cover' is part of the clutch actuator. When you disengage the clutch there is force applied to that part because the cam inside is depressing the bucking bar against the internal clutch spring. Holding it on with only two fasteners might work, for a while, but the chances are good the cover will crack eventually. Especially when the two fastners that are there are only toward the front leaving the rear section unsupported.
Incidentially, that long bolt is there to attach the chain guard that comes with the kit.
No glue is going to fix it. Like was suggested, the cost of a new case would probably be less than having it welded or buying the material to try it yourself.
Proper chain tension will keep the same thing from happening again. A loose chain was the culprit. 1/2 to 3/4" slack is the recommended tension. More than that and you're asking for trouble.
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