Merida Crossway / Bafang 750 watt conversion - drivetrain wear

[Andrew_M]

Hi guys
I just signed up to this forum and I hope I can get some good advice here.
A year ago, I bought a Merida Crossway 20 that had a Bafang 750 watt mid drive conversion. I've had a lot of trouble ever since and it's probably because the motor is too powerful for a lot of the original components.
I have had to replace both wheels with heavy duty ones as they both buckled at different times. I had a new chain and rear cassette put on after about 3 months of ownership. I recently took it back to my LBS mechanic after they had fitted another new chain (a heavy duty ebike specific chain this time). when it came back - it was unrideable. It was shaking and shuddering all over the place and felt like the gears or motor were slipping.
I took it back to the LBS and they have said that the rear cassette is cactus again so it will need to be replaced. It is an 8 speed Shimano Altus I believe.
I am looking for some advice as to if there is a more heavy duty cluster and rear derailleur set up I should look at to get better longevity from these parts.
I keep the bike clean and lubed and regular gear and brake adjustment etc - it's just the massive parts wear that's killing me.
Ay ss greatly received!!

[stts]

Dang. what a mess. it sounds like the freewheel inside the hub could be busted. Replacing the cassette would not fix that freewheel unless the whole rear hub was replaced too. But there is also a freewheel inside the motor. That one could have failed. You have to remove the right hand crank and then remove the motor cover under that crank to get to that freewheel. Those would be the first things to check. These motor can be hard on those freewheels.

[Andrew_M]

thanks STTS
A query though - I just had the back wheel replaced and they put the old cassette back on. If the rear hub freewheel was wrecked, that would have been picked up wouldnt it?
I will check the motor freewheel though.

[stts]

When you get service and it all works great, then there's not much to check out. But when you get service and get handed back a pile of junk, your pretty much stuck with assuming than nothing is right. So check the motor first, as that's the logical starting place. But it's not the easy starting place if you don't have the crank removal tool. Somebody already beat theirs off with a hammer and messed things up. Get the removal tool that works on that motor crank. Then it comes off easy and nothing is damaged. There's youtube videos to guide you and service postings in the BBS threads. I assume its a BBS02 but it could be a lower power BBSHD that has the bigger cooling fins.

[AZguy]

I run nothing e-bike specific

11sp M8000 derailluer on sunrace 11-51t all steel cog cassette with $30 hg701 chain fed by race face narrow-wide ring

Got >3000mi on the last chain and still using the same cassette and ring

Clearly, YMMV

[Andrew_M]

thanks very much AZguy - as a newbie, I had to google what YMMV was but now I get it.
I will have a look into those things once I rule out any other failures through the drivetrain.
It's a shame - the bike is great fun and really practical when its up and going but it does have far too much downtime

[AZguy]

Yes - once you get things straightened out it is quite practical to get plenty of mileage on everything

A proper controller tune and good riding habits (keep the rpm up!!!) make a lot of difference too

[Retrorockit]

8 speed is not a bad place to be. Chains and cassettes wear together. it's not uncommon for a new chain to skip on an old cassette.
First thing is get a bottle of Squirt chain wax and use it often. You can use something else if you want. But Squirt stays where you put it and has a good reputation. Every 30-40 miles is not too often.
Just wipe any loose dirt off with a rag, and put a drop on each chain pin. You might do this after a ride so it can dry.
2nd get some kind of chain wear checking device. if you replace the chain early you might get some more mileage out of your cassette.
Sun Race makes some very affordable 8 speed cassettes. Keep a spare chain and cassette on hand at all times.
I'm running 1500W and just replace chains and cassettes in pairs. It's just the cost of doing business at that level.
With a chain whip, and a cassette socket you can change them yourself. Less work than patching a tire. At 750W the tool less chain connectors should work OK. Don't re-use them. Keep some spares. You can use the LBS if you want to, but this can be DIY if you want.