I broke a chain once on an old bike and didn't break anything else. Had it fixed in a few minutes along the road and was on my way for the rest of the day too.

On our bikes I would think it unlikely a broken chain would break the cases for a couple reasons. The first is there is quite a bit of room under the sprocket cover and for number 2 the sprocket cover would probably take the shot if the chain bunched up under there. Only way I could see a damaged engine case would be if the chain got behind the front sprocket and even then I think it more likely to just scrape it up as opposed to actually putting a hole in it. It could maybe bunch up and break the sprocket cover close to the case and near a bolt and damage the threaded part but again I doubt it would result in a hole. I hope I never find out, the chain that broke on me was cobbled together out of a couple old worn chains I had laying around and had I think 3 master links in it. It was so worn I could bend it sideways and make more than a half circle! I knew that before I put it on but I wanted to ride.

I learned all I need to know about life by killing smart people and eating their brains.
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