Attempting to fix a power assisted eneloop bike

Too Much Power

My home stay mom Kaoru-san’s bicycle was having some trouble and I agreed to take a look at it. It like many bikes in Japan has electric assist. It took some time for me to understand what was happening, mostly because of the language barrier (she speaks English well but talking technical things is another ballpark and I sadly still might as well speak no Japanese). After a few minutes and the help of Google translate I learned the assist was powering while breaking and turning (this is really bad, I personally like to be able to stop). I then took it for a spin and tried to feel it. Those things are incredibly zippy and turning with it powering you is really pretty scary. Having not worked on one of these before it was time for some exploration.

Bellow the bottom bracket is a cover under which is the controller. I figured maybe there were some adjustments that could be made (change the sensitivity of a sensor of something). Jin-san and I got the cover off after some trouble, ending up with a busted off bolt head. Galvanic corrosion plus soft steel is not a good combination. Luckily that bolt only holds on the cover so nothing that can’t be fixed with a zip tie. Saldy the adjusters I was hoping for did not exist.

Next step was to understand the sensor. The chain ring on these bikes is a bit complicated. The toothed sprocket is able to move ever so slightly with respect to the cranks. It is joined to the cranks with a set of heavy springs. As the springs are compressed under load there is probably a touch sensor that then turns the assist motor on. I can’t seem to find a good picture and we were not able to take it apart far enough to get one without a crank puller (I almost brought my little one but figured I never would need it, guessed wrong). Since we couldn’t take it the whole way apart we sprayed some carburetor cleaner (best thing he had) and worked it compressing the springs as much as we could by hand. A bunch of black fun came out so that was a good sign it was doing something.

After putting what we had disassembled of the chainring back together we cleaned and lubed the chain, tightened it, and checked the breaks. Kaoru-san says it is not powering when breaking or turning anymore but she may just be being nice. I do hope it is true though.

A few other fun things about the bike

• It uses 26 1/3 “ tires. I thought this was just an old Schwinn size but this bike is only 8 years old so yeah..
• It has woods type valves and apparently that is common here. I have never seen them before and still really don’t know how you can check the pressure in the without adding air. Anyone?