Shimano EP8 Point of failure and different use cases of grease
, by Rosher Perera, 3 min reading time
This motor has come to us having previously received a service at a different shop, unfortunately in this case we can assume that the service performed is what’s caused the issues within this motor. This specific sprag bearing failure has been caused by over application of the wrong type of grease. Within a sprag bearing you need a low pressure high load type grease as defined within the different industries that use sprag type clutches frequently.
Repairing motors requires a lot of primary research on our part as after care support from manufacturers for motor repair is non-existent, this is evidenced well in discussions around OEM greases. Frequently cited online is Shell Gadus for sprag applications and although this is a non sprag specific general purpose grease it does exhibit the same properties as a more specialised grease making it a viable option, we however do not use this grease as production is less heavily regulated on the cheaper greases and the grease is made with more cost effective raw materials, we instead opt for a more industry specific type.
The sprag bearing in this motor had been over-greased with a lithium or calcium based white grease which is a poor choice for as it’s a general purpose anti corrosive, high pressure grease. As the sprag bearings are sealed within the motor case to begin with they do not require corrosion protection and sprag clutches cannot operate with grease designed for high pressures as it causes them to slip although the main problem in this case was the amount of greasing applied.
The sprag bearings employed within E-bikes require a very thin film of grease on the outside to ensure proper operation, this Shimano specific bearing would prefer slightly more grease than the Bosch specific sprag bearings used in the gen4 and 5 motors as the rollers it uses are greater in height and diameter than the Bosch ones. We believe over-greasing in this sprag bearing has caused the outer sprag race to fail due to the increased pressure and heat within the pinion assembly that locates the sprag in this motor.
In fact this whole motor had been over-greased, we had to spend a considerable amount of time cleaning grease off of all pinion gears and the various PCBs within the motor, in the image below you can see how burnt some of the grease is on the pinion shafts. This is caused by the grease between the pinion gears interacting only upon itself and not acting as a lubricating film between the metal components.
It's worth noting for anyone experiencing a similar situation that a problem like this can cause the motor to throw all manner of codes, as is true with most e-bike motors. An internal failure can be confused for any number of others, in this case the codes we got were torque and speed sensor related. As this sprag interfaces with the main drive axle this makes sense to an extent but can also be a bit of a red herring for the mechanic when working on systems like this one as other satellite sensors are also related to speed and torque.
With all that in mind the final word for this one is going to be, spend some time learning about grease and its different applications as well as how to apply it.
Cheers,
Isaac