Bafang Mid Drive Tear-Down - Advice required.

[JohnnyBBadd]

Hi all

So, I've completed 500 miles on my bafang 750 having purchased it in December 2016. Most of my riding is pretty heavy duty off road and I think I've managed to strip the nylon gear!

Not being one to let others fix my stuff, I like to understand how to do it myself - I've got most tools and a reasonably mechanically minded attitude to things, so decided to strip it down myself.

Having familiarised myself with YouTube video's, I have embarked on my first strip-down, but I just want to check that I am right in thinking that the rubber seal (photo attached) can just be 'dug out' to gain access to the nuts and bearings requiring removal, prior to taking out the main shaft? This seal is not shown on any of the YouTube vids that I've seen as I believe that those are the 'BBS02a' Bafang motors, where mine is the 'BBS02b'.

Any help and advice on what else to look out for on this series of Bafang's would be gratefully received.

 

[Fordulike]

Out of interest, what symptoms are you getting that led you to believe a stripped nylon gear?

 

[JohnnyBBadd]

Well, as I understand it, it is a weak link in the bafang motor. There is no drive either from pedal assist, or throttle, just a high-pitched whirring from the motor when either engaged... It just seems that it is the most likely culprit.

The seal is, as it happens, a press-fit rubber seal with a metallic chassis, and does respond to 'digging out'! However, it will need replacing.

 

[Woosh]

after you open the gearbox, you can generally feel the cogs and even the rotor's cogging when turning the cranks slowly.

 

[JohnnyBBadd]

It would appear that my suspicions were right!

OK. I'm going to order two replacements, as I strongly suspect that I'll be getting through them at an alarming rate. Also, need a replacement crank seal as the BBS02b doesn't have the older style silicone washer between the two crank nuts behind it. Oh, and the two gaskets for the body of the motor!

I'd really like to buy these spares locally to the UK, rather than having to go via Luna Cycles or, even worse, an online Chinese retailer

Thanks for your help so far, Whoosh and Fordulike.

 

[Fordulike]

OK. I'm going to order two replacements, as I strongly suspect that I'll be getting through them at an alarming rate.

I've had no mechanical problems and I'm approaching 4k miles with a maxed out controller. What size chainring are you running?

Like you, I'm doing some nasty off road stuff, but I'm running a 42T chainring and I always keep the motor spinning fast.

 

[JohnnyBBadd]

I've had no mechanical problems and I'm approaching 4k miles with a maxed out controller. What size chainring are you running?

Like you, I'm doing some nasty off road stuff, but I'm running a 42T chainring and I always keep the motor spinning fast.

I use the standard 46T that comes with the kit, with no mods to the controller. I do live in the Cotswolds and in a valley, so there are always very steep hills to negotiate no matter where I ride. My natural cadence is pretty fast too and hardly ever use the small cassette gears, unless i'm going downhill on a road.

Upon taking the motor apart to reveal the nylon gear, I noticed that there was very little grease applied indeed, so I suspect that was the cause of the problem. In addition, you can clearly see that the nylon teeth are all a little frayed, which would further indicate that a lack of lubricant was the problem. I guess I got a Friday build!

 

[tommie]

you sure something didn`t come loose and jam in there and stripped the teeth?

just doesn`t look like wear to me

 

[JohnnyBBadd]

you sure something didn`t come loose and jam in there and stripped the teeth?

just doesn`t look like wear to me

There was no foreign object in amongst the housing, so yep, pretty sure. Everything else is tight, all the bearings and O-rings are as new...