Loose crank bosch ebike

[Bear-uk]

Whoa . Sry, I had no idea .
That’s were food comes from …right?

Apparently so, but it's never had my involvement before

 

[Bearing Man]

Just for info:
If the crankarm is aluminium (aluminum) and you have ridden with it loose for a few miles, it can "stretch" and wear the isis splines inside the crankarm. This means that when you tighten the crankarm to specification the inner shoulder of the crankarm butts up against the end of the crankshaft, but the isis splines are still not tight! This allows slight movement of the crankarm while under load and this will loosen the crankarm again. Adding Loctite to the bolt will only help for a short time in this scenario because the crankarm shoulder and splines will continue to wear quite quickly.
This also happens exceptionally fast on the Specialized SL bikes with the Mahle motors, the crankshaft itself is made of very soft ally and this tends to wear the splines on the crankshaft rather than the crankarm. Result is the same though.

 

[fasterjason]

Just for info:
If the crankarm is aluminium (aluminum) and you have ridden with it loose for a few miles, it can "stretch" and wear the isis splines inside the crankarm. This means that when you tighten the crankarm to specification the inner shoulder of the crankarm butts up against the end of the crankshaft, but the isis splines are still not tight! This allows slight movement of the crankarm while under load and this will loosen the crankarm again. Adding Loctite to the bolt will only help for a short time in this scenario because the crankarm shoulder and splines will continue to wear quite quickly.
This also happens exceptionally fast on the Specialized SL bikes with the Mahle motors, the crankshaft itself is made of very soft ally and this tends to wear the splines on the crankshaft rather than the crankarm. Result is the same though.

Correct, the ISIS spline will become deformed if ridden loose. OP might get some extra life by using Loctite 660 sleeve retainer on the spline interface if the deformation is less than 0.5mm. It has worked for me before.