Since I bought my BMW F650GS Twin 8 months ago I had been riding it for 15 000 miles. During that time the maintenance I performed on it was limited to lubricating the chain and checking individual parts for wear. The dry Spanish summer was a strain on the bike overall but particularly on the chain. In hindsight I believe I should have lubricated it a lot more often than I did. Towards the end of my trip the bike didn’t perform as well as it should have. There was a strange noise coming from the chain as soon as it moved. Accelerating was only possible with much sensitivity on throttle and clutch as a regular immediate acceleration had become impossible without the chain yanking on the gears due to the fact that the chain had started to stretch – unevenly. That meant that I could not simply keep widening the gap between the front and rear sprockets by moving the rear wheel more and more to the back to compensate for the longer chain. So as a result of the unevenly stretched chain links the chain was jumping up and down dangerously when accelerating and decelerating, sometimes even skipping a tooth on a sprocket.

An old or even damaged chain usually damages the sprockets as well. Only changing one of the elements of this little ecosystem means that the unchanged ones will war down the new part very quickly.

A few days after I had received the parts I had ordered I was driving home from work late at night when the inevitable happened. On a little hill at just over 20km/h I heard and felt a tension on the engine building up and suddenly being released. I immediately lost all power and no matter how much I twisted the throttle I was not accelerating. Luckily the street was empty I had just rolled towards a red traffic light. I glanced down onto the chain and saw that one of the double sided chain links had snapped and the chain had jumped off both the rear and front sprocket.

(Photos taken after the fact.)

Unlike a bicycle chain it should be impossible to lift the chain off the rear sprocket. About a millimeter is OK. With great effort I got the half broken chain back around the rear sprocket but it didn’t want to stay on. This should not be possible:

Luckily I was just 500 m from home at that point so I pushed the bike up the little incline and to the parking lot. It was time for some bike maintenance.