Bosch system e-bike transmission slip

Electrically assisted bikes, trikes, etc.
fenmanctc
Posts: 23
Joined: 15 Dec 2013, 10:10am

Bosch system e-bike transmission slip

Postby fenmanctc » 12 Dec 2020, 4:37pm

I have a 2017 Cube Step-thru fitted with a Bosch ActiveLine mid motor, which has done approx 4000 miles since new. I have had a number of issues, all related to Bosch components. First, the battery went totally dead. the cells are fine, but the Battery Management System (a pcb) has failed, resulting in a £550 replacement.
The latest problem is skipping gears, mainly in 7th and 8th, under load.. the hub is Shimano Nexus, but I suspect the problem is the front chainwheel on the Bosch motor. This has only 18 teeth and seems somewhat worn. Is this likely to be the cause, or the hub? The rear sprocket doesn't seem worn at all. I am trying to source a replacement chainwheel, which is proving difficult, as it is dished, and the cheapo replacements aren't, so Bosch must have changed the design of this motor around 20016/17. Anyone know?
Can anybody offer advice on my problems, or share their experience of Bosch stuff? I'm a lifelong cyclist, but the cost of ebike ownership is proving crippling.

Jdsk
Posts: 5228
Joined: 5 Mar 2019, 5:42pm

Re: Bosch system e-bike transmission slip

Postby Jdsk » 12 Dec 2020, 4:41pm

Can you add photos of the relevant teeth?

What type is the chain, how old is it, and have you checked for wear?

Jonathan

fenmanctc
Posts: 23
Joined: 15 Dec 2013, 10:10am

Re: Bosch system e-bike transmission slip

Postby fenmanctc » 12 Dec 2020, 6:06pm

The chain is 3 years old, is a KMC Z610, doesn’t seem to be worn very much( have used a chain wear checker on it). I attach a photo of the chainring. By the way, the hub was adjusted so that the yellow dots lined up exactly in 4 th gear.
A65D40A6-8249-4BB6-AAA3-40D0CF8FF30D.jpeg
Image Attachments
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bob simpson
Posts: 173
Joined: 16 Mar 2007, 3:55pm
Location: West Lothian

Re: Bosch system e-bike transmission slip

Postby bob simpson » 12 Dec 2020, 7:23pm

I would say that the cog looks very worn. I would replace it and also the chain.
If the cog is offset you can get cheaper FSA ones.