Shimano EP8 point of failure
, by Rosher Perera, 4 min reading time
Shimano EP8: A Common Point of Failure Explained
Within this unit the drive side bearing has failed and in this instance there’s not even anything left of it. This bearing has failed due to excessive mileage or poor conditions. We are usually able to fix this and replace the failed bearing however this is dependent on the state of the bearing seat itself as there is quite a lot of the old destroyed bearing race still left in it.
Why the Drive-Side Bearing Fails
This is a common point of failure in ebike motors as it is the moving part of the motor that sees the most wear over the lifespan of the unit. Motors are designed with this information in mind hence why the driveside bearing is significantly bigger than the non-driveside bearing in this unit, because although the crankshaft is driven evenly in the shimano motor more pressure is generally always applied on the driveside bearing in an ebike due to the forces going through the drivetrain.
Sealing and Water Ingress
The two halves of a shimano ep8 motor are sealed with silicone in order to stop water ingress, however the external crankshaft bearings in this unit are unsealed, instead relying solely on rubber gaskets on the outside of the bearings which are designed to keep water out of the bearings. However due to the aforementioned forces the crankshaft bearings are subjected to and the pitching of the crankshaft due to the torque of the motor these seals are known to fail and then as a result of this the bearings will follow suit.
Internal Components and Long-Term Reliability
We are able to replace the unsealed external bearings with sealed units which we tend to do as a matter of course for shimano motors specifically as there is no real downsides and bearings which utilise modern labyrinthine seals offer an extra layer of protection over the bearings shimano use from the factory
Other moving components within the motor include:
Pinion shafts
The internal unsealed bearings are less of a worry because they are operating within the sealed units where there will be little to no water ingress if all is well with the external bearings, they therefore have a much greater service interval. Other moving parts within this shimano motor and other motors are the pinion shafts and sprag clutches.
Sprag clutches
The pinion shafts are responsible for gear reduction within the motor, this is necessary as electric motors are able to spin a lot faster than a person's legs, there are 3 stages of reduction within an ep8 although the ratios are not disclosed. Pinion shafts are not really a point of failure as they are metal on metal and with correct lubrication have a lifespan far longer than any other components within the motor.
Sprag clutches are employed at 2 points within this motor. These serve to act like a rear hub in the context of the motor allowing the crankshaft to spin freely when it is undriven in order to allow the bike to act like a freewheeling bicycle as opposed to a fixed gear. Within a shimano motor, sprag clutches pose a slight problem as replacements are only available from shimano and cannot be swapped for other manufacturer parts, as is possible with general bearings for instance. However sprag clutches themselves have a relatively low failure rate as the mechanism they employ is essentially all metal on metal and as they are sealed within the motor, with no water ingress they should last a long time.
Preventing This Issue
Overall this is a run of the mill issue we see quite often and as with most of the work we carry out the issues with this motor stem from water ingress. This is something that you can guard against by caring for your bike correctly by:
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Avoiding pressure washing directly at the motor area
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Periodically re-greasing the external rubber gaskets on EP8 motors
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Addressing unusual noise or roughness early, before bearing damage progresses
Otherwise feel free to drop it into us and we can fit some proper sealed bearings for you!
Cheers,
Isaac