Your local shop has told you to replace your chain. The last two times around. And you have chosen to ignore it.The chain has loose and tight spots, depending on where in the rotation you check it. Or it already hangs down to the ground, almost anyway, looks rusty, and you can lift the chain off the sprocket by over 1/4 inch.
So what happens when your chain breaks or comes off? If you are lucky, it just comes off, falls on the road, and hopefully your buddy behind you won't run over it and crash.
Or it could whip up and hit you, the rider...I have seen it on a race bike once...the chain made a hole in the tail section and hit the rider in the back.
The chain is going at the speed of the bike you see, and the energy it picks up from going around is at least as high as crashing at 100mph, and that's the speed when I crashed and broke my hip, so I have experienced those forces at 100mph first hand and believe me, it's violent.
Or, as in this case on this picture right here, the chain doesn't break, but "just" comes off the sprocket and balls up under the chain cover and breaks the crank case. And if you are lucky, it won't lock up the rear wheel and you won't crash.
This guy was lucky. The bike is still in pristine condition, really nice actually, on the outside, but what this seemingly innocent little crack there means that it's basically done for, NFG, engine broken beyond repair.
In some cases, it can be fixed. If the crack is in an opportune place and you have a really, really good welder at hand that is willing to work on (not the usual "no, we won't touch") motorcycles, you might be able to get that welded.
If the crack is in a place like on this GSXR1000 though, i.e. in the walls on the precision bored hole that holds the water pump, there is pretty much no way you can fix this on or off the bike, since it would have to be machined afterwards to take the pump shaft again, and the filings from the machining will get into the engine, not to mention that it is somewhat difficult to get the motorcycle under a drill press, sideways and square.
Only solution in this case: new engine. On some bikes that would exceed the total value. So if you would like to avoid this fate, learn how to check your chain for the correct tension, and for "tight spots", which is hard to explain in writing, but if you come by anytime during business hours, I'll be happy to demonstrate, for free, and with pleasure. After all, I like my fellow motorcycle riders to stay alive. I hate going to funerals.
And don't forget to lube your chain every 300 miles or so, that'll make your chain and sprockets live a whole lot longer.
