Bosch Mid Drive Inspection


Active Member
Oh hi,

As discussed in another thread I mentioned I would inspect my motor. The bike I bought was a demo bike with 250 miles on it. It was clear that it was demo'd well as it had mud in all it's crevasses. I now have about 600 miles, and after reading about the various hardcore rides some people have but the motor through I thought I better check mine.

First problem was my Crank removal tool was not the exact fit, it seems Park Tool CCP-44 is, can anyone can confirm that? I made a temp tool but would prefer the proper tool.

On the sprocket set we can see corrosion on the nut that hold the pedal arm on the crank.

Bosch Inspection1.jpg

Also we can see some corrosion on the inside of the crank axle, the following picture is from the right side looking thru the axle. Note the splines on the right side have grease, I noticed no grease on the splines on the sprocket side

Bosch Inspection6.jpg

Here is the left side case show some water spots

Bosch Inspection3.jpg

I see no serviceable items. Not sure what would have happened if I removed the lock rings on the axle. Hopefully the axle slides out and one could easily replace the bearings...does anybody know?

One surprising thing to me was how small this motor is, the plastic covering makes it look a lot larger. I cleaned it up the moter, ran a oil rag through axle, lubed the splines and stuck it back together. BTW those water spots are no big deal and common on AL, incase that worries anyone. I just sprayed it with dry lubricant as a protector.

Here is a picture of the 15t sprocket, which seems fine.

Bosch Inspection7.jpg

Must say it is thin, the black is a coating and you can see it on each tooth...anyone know why?

A side note, my rear brakes made a different sound on the last ride...well they wore down to the retainer clip. Didn't seem to damage the rotor and I put on new pads both front and back. (but only lasting 600 miles is surprise, the front actually had lots of life...I am afraid of washing out the front so I tend to use the rear brake more)

Finally the motor appears quite water tight, my concern would be bearing seals if exposing the motor to a lot of water...same as any other bike.

Has anyone seen a video of bearing replacement?

Also I bought the special cog tool to get the sprocket off. You could remove it by other means, but you might damage it.

(I posting now, may come back and edit grammar)

Shea N Encinitas

Active Member
Cool to see the guts of your motor. The black finish may be an oxide finish similar to anodizing but for steel parts, the teeth have perhaps been worn off. Do you have a torque wrench for reassembly? That nut is marked something like 54 nm on my bike. I ended up using blue loctite on my crank nut. I sure hope someone comes out with replacement motors that basically bolts in place, or I'm going to have to design and machine one myself in a few years. -S


Active Member
Oh hi,

I bought the cog tool from my bike shop. I'm going there to get extra sprockets, I could get one and send it to you if you have problems finding one. I also contacted Park tool and told them to make one :) Actually they have a cog tool, but it is not clear if it is the same size. I will investigate that more.

The coating actually feels like rubber, but I could believe it was some sort of metal coating. and I agree it is worn off the teeth.

@Shea N Encinitas what do you think the crank nut is made of? It was so light that I almost thought is was synthetic. (I assume I'm wrong, but if I'm correct, Loctite could be a bad thing as it reacts with various synthetics)

Yes I have torque wrench both, analog and digital, and I only trust the the analog ones!