I opened my hub motor and found this....

[madnomad]

Hi guys. I've just taken my motor apart to tap some new threads for the cover plate as all the old ones had been stripped. When I went to put it back together, there was a grinding sound in one direction so I took the motor out of the casing and found this:

The magnetic ring has broken.

What does this ring do? Does it make much difference if I remove it? Is it possible to get a spare one from somewhere? It's a BMC V4C.

 

[madnomad]

As it had shattered I decided it definitely had to be removed before any more broke off and got caught in the gears. But it turns out its not actually a magnet. I dont really know what it is but it looks important. Does anyone know what it is and if I can get a new one? I've contacted BMC who have told me that they dont sell spares, but does anyone know anyone else that does? If its not possible to buy spares for BMC motors then I definiely wont be buying a new one, especially as they seem to be so poorly made. This motor is less than 18 months old.

 

[izeman]

Go to em3ev.com. Paul sells MAC clutches/freewheels that should fit.

 

[teklektik]

That ring is the plastic retainer for the sprags that are the heart of the V4 freewheel clutch. It is held in place by a bunch of little cylindrical legs with blobs on the ends that poke straight down in between some of the sprags and click into mating holes so the ring appears as a roof supported by pillars that sandwich the sprags in place.

This ring sometimes fractures when the clutch is pounded with too much torque very suddenly (voltage>60V or so, CA ramping not set low enough). However, since it it is a fraction of a millimeter from the side plate (you can see the 'rub marks' in your photo of the clutch rubbing the plate), it can't go anywhere and the many legs hold the individual fractured pieces in place. I've run countless thousands of miles with multiple breaks in this retainer and each broken piece continues to retain the sprags underneath it.

Unfortunately, by removing this part you have broken the clutch and need a whole new one.

The source of the grinding noise you heard is unclear but is unlikely it was related to the clutch or this part. It may simply have been the clutch rubbing the side plate - which is unsettling, but not a terrible thing.

You can get these from ebikes.sf. As izeman said, a MAC gear cluster will also work at a fraction of the price. You can get one of these from EM3EV. The MAC clutch is slightly different so you want to also get new MAC gears to assemble an entire gear cluster. It's also a bit thicker and you may need to omit the outside circlip near the cover plate (I use a thinner inner/outer clips so they fit okay - you'll just have to see what fits in your case). You will want to email and get Paul to include a 17mm wave spring washer to stick on axle shaft under the side plate to help space the clutch away from it. While you're at it, request a new shaft key - I'm guessing yours may be beat up from some rough clutch engagements.

There's a few posts here on ES about the teardown/assembly process for MACs - which are essentially the same animal, so no problem there.

 

[izeman]

Yes. As teklektik wrote: get some new gears as well. Wanted to add that but was too fast with hitting 'send'

 

[madnomad]

I only removed a couple of the sprags, and have now put them all back in place, which was pretty fiddly, but its now missing the plastic retainer in places. The motor seems to work, at least for the time being, hooray! The grinding noise I described in the first post was just one of the cylindrical blob things which had come out and was inside the casing, which prevented the motor from going back into the casing as far as it should. I'm going to buy another one and hope my motor lasts until it arrives. I think with my level of expertise it would probably be wiser for dish out the extra cast for a BMC one so I dont have to change the gears? Is it really so much cheaper to get a MAC one if you have to buy new gears as well, especially with the cost of time taken into account?

Another question... sometimes if I accelerate too quickly, my motor makes a horrible grinding sound. Would this be because this plastic retainer was broken? Or could there be something else wrong?

 

[izeman]

the grinding noise is most probably the clutch/freewheel over loaded and slipping. you should dial down your controller's phase amps.

 

[DAND214]

Clutch from EM3ev fit fine in my wife's BMC V1. Yeah you need new gears with the clutch but the are better than the old ones.

Dan

 

[teklektik]

Is it really so much cheaper to get a MAC one if you have to buy new gears as well, especially with the cost of time taken into account?

C'mon - I gave you links to the pages with prices - $50 vs $200. If you buy from EM3EV, I would recommend picking up a spare if you can afford it, since the second will ship just about for free.

The choice is not clear cut - I find the BMC clutch to be slightly better at holding high torque. The composite grey MAC and blue BMC V4 gears are of equivalent strength with the MAC gears slightly wider and very slightly noisier (the really old white BMC V1/eZee nylon gears are like butter by comparison). Both Ilia and Paul give great support. Ilia at Ebike SF is certainly closer and the shipping and delays are greater from Hong Kong. With the Chinese new Year thing happening shortly, there may be long delays shipping from China, so... (?)

Another question... sometimes if I accelerate too quickly, my motor makes a horrible grinding sound.

As izeman said, too much torque.

• If you have an EM3EV or Lyen 'Infineon' (Xie Chang) controller, then it's recommended that the phase amps be about 2x the rated amps - not the 'standard' 2.5x. 'Block time' is for smaller DD motors and for gear motors you should set it to 0.0 (the programmable amp limiting is disabled off the line for 'block time seconds', so if this isn't Zero, you will pound the clutch with essentially no limit on controller amps regardless of your amp settings).
• Since you have a CA V3, adjust the UpRate to a lower number so the throttle is applied more gently. See the Guide. I run 65V, 73V HoC (silly for a BMC 8T) and smoked a few clutches getting this adjusted properly (not too much WooHoo!). Once figured out, though, it runs rock solid.
• It seems to help if you accelerate and 'engage at speed' gently for a hundred miles or so to work-harden the faces of the clutch before you slam the dickens out of it. Once your clutch has chattered, it generally seems that some deformations are formed in the face and it will be more likely to chatter in the future (slow degradation to uselessness as damage builds up). If a clutch is never pushed to break free and chatter, it generally seems to run forever - that is, it doesn't seem to naturally degrade over time if not abused...

As another thought, if you had to really beat the crap out of the side covers to get them off, you may want to replace the bearings and seals while things are apart. There's some stuff about that in my build thread. If you dressed the burrs off the shaft shoulders and the covers just slid off nicely - don't bother. In any case, grease the seals and be careful during re-assembly so they don't tear.