Yamaha ebike motor: Chain seems to skip on the forward sprocket.

[Tintinmilou]

We bought an MBK (Motobecane) ebike for my wife. It has a Yamaha motor on it. It's European spec, so PAS only. Whenever I start pedaling on it, it seems like the chain is slipping off the motor sprocket for maybe a half turn of the crank, and then the motor kicks in and it smooths out. Every time I coast a bit and then start pedaling, it does this, making an awful noise. Has anyone encountered this? I'm thinking it might a problem with the torque sensor?
Full disclosure: we bought it at a discount house, so no warrantee. It was a new bike, but perhaps it ended up there because of this problem.

 

[Rotos Aerial]

Hi There,

Just solved chain skipping issue on high-power mid-drive home-built Bafang e-bikes such as fat tire or full sus. This universal problem seems to be due to the gear mechanism on a spring-system that adjusts chain tension. This works fine for normal pedaling, but by adding power it causes the chain to be dragged over the gears. You don't need that many gears anyway, so I finally took 4 links out of chain and eliminating top and bottom gears minimum. Now the lower idler gear is pointing straight toward front sprocket at low gear. Adjust limiting screws on rear derailleur makes sure chain stays within this range. This removes much slack and now there is no skipping, and allows for high speed and good climbing. I use a large front sprocket for speed and have a smaller right behind it I can switch on trail if needed with crank puller. One could also try just locking in one gear and eliminate shifting or the idler wheels. New chain and cassette can help, but this is finally a great solution for me at least. Will make video today of this mod on my Giant Stance Full suspension Bafang BBSHD mid-drive with large front sprocket I think 42 teeth.

 

[HumanPerson]

Hi There,

Just solved chain skipping issue on high-power mid-drive home-built Bafang e-bikes such as fat tire or full sus. This universal problem seems to be due to the gear mechanism on a spring-system that adjusts chain tension. This works fine for normal pedaling, but by adding power it causes the chain to be dragged over the gears. You don't need that many gears anyway, so I finally took 4 links out of chain and eliminating top and bottom gears minimum. Now the lower idler gear is pointing straight toward front sprocket at low gear. Adjust limiting screws on rear derailleur makes sure chain stays within this range. This removes much slack and now there is no skipping, and allows for high speed and good climbing. I use a large front sprocket for speed and have a smaller right behind it I can switch on trail if needed with crank puller. One could also try just locking in one gear and eliminate shifting or the idler wheels. New chain and cassette can help, but this is finally a great solution for me at least. Will make video today of this mod on my Giant Stance Full suspension Bafang BBSHD mid-drive with large front sprocket I think 42 teeth. View attachment 16170View attachment 16171

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