Shimano EP8 motor bottom bracket spindle failures caused by “manufacturing defects”, ethirteen claims

Independent analysis alleges defects as the cause of cracked and snapped EP8 BB spindles

Shimano EP8 motor

Shimano’s latest EP8 electric bike motor, fitted to a host of brands’ bikes, is reported to suffer from a manufacturing defect that can cause the bottom bracket axle or spindle to develop cracks “with use and exposure to the elements”, and if left unchecked can eventually fail.


These findings are the result of an independently commissioned investigation by e*thirteen, after the brand became aware of reports that EP8 spindles were failing on bikes fitted with its ebike cranks.

e*thirteen is one of the biggest OEM suppliers of cranks on electric mountain bikes. The brand was made aware of failures occurring when the EP8 motor is used with pedal cranks made by brands other than Shimano, including e*thirteen’s e*spec ebike-specific cranks.

The investigation has led e*thirteen to produce technical service bulletin 157 (TSB), published on its website on 14 October 2021. The brand suggests EP8 owners should inspect their motor’s spindles for damage or cracks originating from the drilled hole used for the pedal crank retainer hook, located on the splined portion of the axle.

According to e*thirteen, the safety inspection is relevant to all EP8 owners, regardless of what cranks are fitted.

“e*thirteen’s analysis suggests that some Shimano EP8 spindles may have manufacturing defects which, over time, can develop into cracks with use and exposure to the elements,” reads TSB 157.

Shimano EP8 electronic bike motor spindle failure
The axle can crack and eventually fail, according to e*thirteen’s bulletin.
Alex Evans / Our Media

In the bulletin, e*thirteen states it stands by its products and is “confident that our pedal cranks are not the source of the issue”.

According to the TSB, only Shimano’s EP8 motor is affected. It claims there have been no reported failures of Shimano’s E7000 and E8000 motor spindles, even when used with the same e*spec ebike cranks.

Muddying the waters

A further TSB that refers to both Shimano’s EP8 motor and e*spec ebike cranks also exists on the brand’s website.

TSB 156 addresses a reported issue where the crank preload end cap can loosen and fall off, eventually causing the pedal cranks to become detached from the bottom-bracket spindle.

This occurs if the cap is not correctly tightened or the factory-fitted threadlock hasn’t been adequately applied, and if the crank arm’s pinch bolts aren’t tightened to their correct torque.

ethirteen espec electric mountain bike cranks preload cap
TSB 156 refers to both the EP8 motor and e*spec ebike cranks.

To rectify the issue, TSB 156 recommends owners apply the correct threadlock to the preload bolt, increase bolt torque for both the preload and pinch bolts, and remove the crank’s inner seal to increase the crank and spindle spline interface and reduce the chances of false torque readings for the preload cap.

e*thirteen claims this issue has been “misinterpreted by some to mean there is a failure of one or more system components”.

Reading between the lines, we suspect the misinterpretation e*thirteen is referring to is regarding the EP8 bottom bracket axle spindle failure noted in TSB 157.

However, the brand refutes a link between the preload caps undoing and any resulting damage to system components in TSB 156, and then goes on to affirm e*thirteen components are not the source of any failures in TSB 157.

“That is not the case, but all cranks should be checked for proper tightness before riding, and initial installations procedures should be updated,” reads TSB 156.

Reports of EP8 spindle failures online

Shimano EP8 electronic bike motor spindle failure
We managed to see a broken EP8 spindle in real life. This is the portion that was attached to the crank arm.
Alex Evans / Our Media

The most prominent reports of EP8 axle failure exist on two EMTB forum threads. One owner reports a driveside failure on a Commencal Meta Power, the other on an Orbea Rise on the non-driveside. Both bikes were fitted with e*thirteen cranks.

Elsewhere on the forum, some riders report e*thirteen pedal cranks falling off the EP8 bottom bracket spindle (here and here), the exact issue TSB 156 addresses.

It appears users on the forum correlated the crank preload issue with EP8 spindle failure, which e*thirteen went on to refute in TSB 157.

In a closed Facebook group called Shimano EP8 Owners, there are also reports of EP8 spindle failures.

What do Shimano and e*thirteen say about these failures?

Shimano EP8 electric bike motor spindle crack
In TSB 156, e*thirteen shows images of a cracked EP8 spindle.

We asked Shimano and e*thirteen for comment on the spindle cracking issue. Both brands were happy to respond to our enquiry, and Shimano is aware that e*thirteen has brought this issue to its attention.

Shimano’s overarching advice is for consumers to only use Shimano-approved pedal cranks on its EP8 motors.

“Shimano advises that only approved crank arms should be used with its DU-EP8 drive units,” reads Shimano’s statement.

“Approved crank arms are listed at and are communicated towards bicycle manufacturers. These combinations meet our strict and exacting quality standards. Our drive units are not tested for use with third party crank arms.”

Shimano EP8 electronic bike motor spindle failure FC-EM600 pedal cranks
These Shimano FC-EM600 pedal cranks are approved for use with the EP8 motor.
Alex Evans / Our Media

The only Shimano-approved pedal cranks listed on Shimano’s website are the FC-EM600, FC-M8150 and FC-EM900, all of which are available to buy aftermarket from various retailers.

Meanwhile, e*thirteen’s response places the ball firmly in Shimano’s court.

“When we see failures like this, it is incumbent on us to find the root cause and, if it is within our control, provide a resolution,” reads e*thirteen’s statement.

“To replicate field failures, we had to look outside of the required ISO and EN testing requirements as those tests were passed successfully. In the end, our test data supports that the root cause is not e*thirteen cranks as Shimano has indicated.

“This data covers comprehensive third party metallurgical analysis in addition to results from a rigorous test battery of corrosion testing combined with ISO Fatigue. We have shared the results with Shimano and select OEM customers.

“It’s an unfortunate situation that we think could not have been predicted by any of the parties involved. e*thirteen is at the table with bike brands to find a mutually acceptable solution that first takes care of keeping people on their bikes. We hope Shimano will join us at that table soon.”

Shimano EP8 electronic bike motor spindle failure e*thirteen e*spec Plus pedal cranks
The e*thirteen e*spec cranks are not approved for use with the EP8 motor, Shimano says.
Alex Evans / Our Media

Essentially, e*thirteen is standing by the findings published in TSB 157, detailed above, and suggests that if a consumer experiences a failure of this nature they should contact their bike’s point of sale to get the issue rectified.

Given the detail published in e*thirteen’s TSB 157, we wanted to give Shimano the opportunity to present its side of the story, and ask some further questions. Shimano’s answers to our questions are published below verbatim.

What can consumers expect to happen if their EP8’s spindle fails?

“The reported cases of drive unit spindle breakages on our DU-EP800 drive units were combined with non-Shimano cranks. We recommend only Shimano cranks for usage with our drive units. The question of what happens with this combination is for the manufacturer of that combination to answer.”

What would happen if a consumer noticed their axle was cracked in the way described on e*thirteen’s TSB?

“If consumers use the recommended cranks, there should not be any issue – this combination meets our strict and exacting quality standards. If in doubt about such components, we recommend speaking to your bicycle manufacturer.”

What is Shimano’s take on e*thirteen’s metallurgic analysis findings?

“The metallurgic analysis was conducted to discover root cause. The cause is due to the difference in design from Shimano’s crank, which causes increased stress around the spindle hole.”

Does Shimano know why the spindles are snapping?

“Yes, we understand how and why spindle breakage may occur when some non-Shimano cranks are used with our DU-EP800 drive unit. Non-recommended 3rd party cranks can make a crack in the spindle because the difference in design from Shimano’s crank causes increased stress around the spindle hole. Under this condition, with each ride the crack can expand, and this can result in a spindle breakage.”

How many instances of this problem has Shimano encountered?

“There are no reported cases of spindle breakage of DU-EP800 when assembled with Shimano’s cranks. Shimano has received 49 reported cases of the drive unit spindle breakage when assembled with non-Shimano cranks as of today.”

Merida eOne-Sixty electric mountain bike with Shimano DU-EP800 motor
Shimano’s EP8 motor is fitted to bikes from a wide range of brands.
Russell Burton

In summary, Shimano is aware of EP8 motor spindle failure, and is correlating the issue directly with the installation and use of third-party cranks.

Shimano also claims this issue is entirely isolated to non-Shimano cranks, stating it is aware of 49 reported cases of spindle failure.

According to Shimano, design differences between Shimano and non-Shimano cranks cause the axle to crack and eventually fail. Shimano doesn’t state what those design differences are, however.

Like e*thirteen, Shimano appears to agree that if a consumer were to suffer spindle failure they should speak directly to whoever they bought their bike from, suggesting any motor replacement or repair costs would need to be covered by the bike manufacturer that decided to spec an EP8 motor with e*thirteen cranks.

Why aren’t bike testers reporting this?

2022 Yeti 160E T1 electric mountain bike
The Yeti 160E Alex tested didn’t suffer from spindle failure, but the motor did get an E010 error code and had to be repaired under Shimano’s warranty.
Andy Lloyd / Immediate Media

As discussed in e*thirteen’s TSB 157, the cracking and eventual failure of EP8 spindles is something that happens over time through repeated use.

We suspect the amount of riding required to replicate this problem far exceeds the number of kilometres an average bike tester will do on any given model.

Bikes sent in for testing are usually carefully prepared by brands to pick up any assembly issues, and then are checked before testing by in-house mechanics or the testers themselves.

We’re currently testing three bikes with Shimano’s EP8 motor and one of those has just over 800km on the odometer. However, all  are fitted with Shimano cranks. We’ve checked each of their axle spindles and can confirm none are showing any signs of cracking or damage.

What should you do if you have e*thirteen cranks on your EP8 motor?

Shimano EP8 electronic bike motor spindle failure e*thirteen e*spec Plus pedal cranks
Many manufacturers spec e*thirtreen cranks with the EP8 motor.
Alex Evans / Our Media

Any rider who owns an ebike with an EP8 motor fitted with e*thirteen cranks currently has two options.

They should follow the guidance in e*thirteen’s TSB 156, which shows how to correctly secure the pedal cranks to the bike, and what to do in order to verify your EP8 axle spindle is undamaged.

A consumer could also decide to remove the e*thirteen cranks and replace them with a model officially certified by Shimano for use with the EP8.

Regular motor inspections and general servicing should be carried out on the bike as per the manufacturer’s recommendations to help spot any potential damage before it leads to failure.

What should you do if you discover your EP8 motor’s spindle is cracked or damaged?

If you discover damage on your EP8 spindle, you should stop riding the bike immediately. Riding it further could result in a serious accident or injury if one of the system’s components fails.

Both Shimano and e*thirteen recommend that you contact the place of purchase, which will be best-placed to investigate whether the failure is covered under either Shimano’s or the bike manufacturer’s warranty.

What are the bike brands saying about this?

Commencal Meta Power TR Ride Sand electric mountain bike
The Meta Power TR Ride was one of the bikes fitted with an EP8 and e*thirteen cranks.
Commencal Bikes

e*thirteen cranks are commonly specced on electric mountain bikes fitted with Shimano EP8 motors, by bike brands including Commencal, Marin, Orange and Orbea, among others.

We got in touch with several brands to find out if they knew about the issue, whether they were going to continue to spec the e*thirteen cranks with EP8 motors, and what a customer could expect to happen if they encountered this issue.

Commencal – which has sold a number of its Meta Power electric bikes with an EP8 motor and e*thirteen crank combination – replied to our inquiries.

The brand told us it was aware of the spindle issue and has been in contact with both Shimano and e*thirteen about it.

“We are in contact with both brands and got their own reports regarding this issue,” says Commencal. “[The] topic has been closed from Shimano[‘s] side but e*thirteen is still investigating with independent labs.”

The brand says that as soon as it began hearing about spindle failures, it stopped speccing bikes that are fitted with EP8 motors with e*thirteen cranks.

“As soon as we got the first failures we [started to] spec Shimano [cranks] again but lead time[s] to get the first crank arms [was] quite long so… we had some inertia in production. All bikes [have been] assembled with Shimano cranks since 2021 April.”

As of April 2021, all of Commencal’s EP8-equipped bikes have been specced with Shimano cranks, but this change has taken some time to filter through to consumers because of the time it takes for fully built bikes to get to the shop floor.

For consumers who do have an EP8-equipped Commencal with e*thirteen cranks, the Andorran brand is offering to replace the e*thirteen cranks with Shimano ones, regardless of whether they’ve experienced issues with their EP8 spindle or not.

Commencal Meta Power SX Ride electric mountain bike
Consumers should begin to see e*thirteen cranks less and less on Commencal’s bikes. Current Commencal owners who have e*thirteen cranks can have them replaced free of charge.
Commencal Bikes

“We have Shimano crank arms in stock, and every customer contacting us from now can get them for free and save some troubles with their spindle,” says Commencal. “We will have them soon available in all our subsidiaries (Canada, USA, Chile, Australia, NZ and Reunion Island) to reach all our customers worldwide.”

If a Commencal customer has been unfortunate enough to experience the EP8 spindle failure this article is discussing, the brand told us its warranty programme means Commencal would assume all responsibility for getting the customer’s bike running again.

“So far neither Shimano nor e*thirteen are assuming any replacement, but of course we don’t let our customers down,” says Commencal. We bought drive units and crank arms, we are replacing at our cost all damaged parts and are covering labor [and] shipping costs that might occur. This is part of our COMMENCAL Care program, we consider a warranty case should have no cost at all for any of our customers.”

This, of course, is good news for Commencal customers with EP8 drive units and e*thirteen cranks, and we’re hopeful other brands will follow suit.

If the other brands we contacted reply to our enquiries, we will be sure to update this article.


If you’ve experienced a Shimano EP8 bottom bracket spindle failure, let us know in the comments below.