Yes - you have a woodruff key on the flywheel. If you backfire hard enough to "jerk" the engine the opposite way that it is spinning, the woodruff key can be sheared off. This prevents damage to the crankshaft because of the large rotating mass of weight the flywheel has. Because your crankshaft is pressed together, backfiring can also cause the crankshaft to twist out of alignment. This will cause major problems. I'd take a look at the source of the problem. Is it just backfiring after you have hot pipes, and shut down too quick. That will send tons of unburned fuel in to the hot pipes and cause a "pop." If so, let her idle down for a minute before hitting that kill switch.