The ISIS crank interface was once commonly used on mountain bike cranksets but eventually phased out as external BB cranks using different interfaces started appearing on the market. Recently new life was given to the interface standard when Bosch™️ began using it on their ebike motors. The ISIS interface can be very robust but is highly reliant on the tolerances laid out in the standard. Spindle manufacturing in particular can be a complicated process. e*thirteen's Bosch e*spec cranks are QC'ed at a 100% rate to ensure that our spline shapes are within the specifications of the standard.
Below are a few troubleshooting tips if you're having repeated loosening issues with your e*spect Bosch cranks. Keep in mind that once a crank has been ridden loose, it often damages the interface enough that it needs to be replaced.
First verify the spindle is not undersized:
- A good test to determine a potentially undersized spindle is to attempt to press a new crank on by hand. When this is done, there should be a 3mm+ minimum gap between the face of the crank and the stop on the ISIS spindle. Anything close to 3mm or less and an undersized spindle could be the culprit for the loosening issues. If your crank has a self-extracting bolt hardware, you will either need to remove the self extractor and bolt or thread the bolt in slowly as you are using your hand to press the crank onto the spindle.
Next, verify/perform the following:
- When the crank arm is fully installed to torque spec, the face of the crank needs to be bottoming out on the stop on the ISIS spindle. If it is not, the crank should be removed and reinstalled until it does. If the crank is not butted up against the spindle stop, it could have a tendency to want to walk off the splines.
- Consider installing the crank bolt with some Loctite 222 or 242.
- Verify crank bolt torque spec after the first and 3rd rides.