Bmc hub motor runs but won't spin..

[Jsblastoff]

Need help,

My bmc hub motor has a problem. I went for a ride. I turned off the bike for an hr. When I tried to start it back up it wouldn't spin the wheel. I could here the motor spinning in the hub but would not engage the wheel. I turned on and off and unplugged / replugged all connections. Started to work then stopped. Started heading home. Motor cuts out. Still can hear it spinning in hub. Then starts working again, then stops. Always I can hear the motor working in the hub, but sometimes won't engage the wheel. Usually when I turn on the bike the throttle doesn't work until the screen exits the startup screen, a few seconds. I notice when the motor won't work it doesn't have this lag the motor spins as soon as lights on but won't engage the wheel.
Any help appreciated.

 

[wasp]

welcome to es
probably stripped gears
wasp

 

[d8veh]

When you hear the motor spinning, but there's no drive, there's three main possibilities. First, it might be going backwards. If you lift the wheel off the ground, it might turn slowly in the direction of the motor. Secondly, the clutch might not be engaging properly because avroller is stuck. Thirdly, broken teeth in the gears. You can normally hear that and it jumps a bit.

If it works sometimes enough to drive the wheel some distance and then won't engage, I'd say it's the clutch.

 

[Jsblastoff]

Thanks for fast response!

Sounds like it must be the clutch because When it does engage I can drive it a ways. "Avroller" don't know what that is, gonna do some research. Is this something I can fix myself? Thanks!

 

[d8veh]

Some clutches are rivetted, so not serviceable. You can get replacements though. It's time to open the motor.

 

[cycborg]

"Avroller" don't know what that is, gonna do some research.

“avroller” is a thumb hitting the “v” key instead of the spacebar. Probably don’t want to spend too much time researching that. :wink:

 

[teklektik]

When I tried to start it back up it wouldn't spin the wheel. I could here the motor spinning in the hub but would not engage the wheel.
...
Started heading home. Motor cuts out. Still can hear it spinning in hub. Then starts working again, then stops. Always I can hear the motor working in the hub,
...
Usually when I turn on the bike the throttle doesn't work until the screen exits the startup screen, a few seconds. I notice when the motor won't work it doesn't have this lag the motor spins as soon as lights on but won't engage the wheel.

Questions:

• How old is this motor and controller?
• What kind of controller do you have? Sensorless?
• What do you mean by "Motor cuts out"? Was it running along and just stopped working or did it fail on a getaway or after a power cycle?
  (Related: Do any of the failures suddenly occur while running the motor or only after a power-up?)
• Does the motor ever make a chattering machine-gun sound when you open the throttle?

Here's the thing - the BMC clutch is a sprag clutch and it's hard to believe they all are slipping - I've never seen that failure mode except when the clutch has been greased with moly - regular grease won't make it slip. The BMC or MAC gears are pretty indestructible - the clutch usually gives up before the gears are harmed so I tend to discount them.

The business of the 'startup screen' and odd behavior on powerup makes me wonder if this is a sensorless controller that is a little neurotic and starting in reverse occasionally. As posted above, the silent running without engagement and absence of chattering sounds like the motor is in reverse.

When this failure happens, lay the bike over or lift the wheel and try turning the wheel in reverse. If the clutch engages you will feel drag rotating it in reverse but no drag rotating it forward. If you do this and keep finding the clutch engages properly by hand then I might turn a little attention to the controller if it's sensorless or has a reverse switch that might be wonky.

Just a thought....

• If it is the clutch, you can get replacements from Ilia at EbikesSF or use a MAC 500 clutch from Paul at EM3EV- they are interchangeable. See this post about BMC cluster replacement. There are other posts on ES about MAC teardowns (see SM's thread with lot's of PICs - here) - getting to the clutch on either is essentially identical.
  
  The BMC and MAC clutches cannot be opened or serviced and removing the gears without damage is problematic. BMC clutches come with new gears as a cluster. For the MAC, you buy the clutch and gears separately and assemble the cluster (recommended over trying to reuse the old gears).

 

[Jsblastoff]

Motor and controller are 3 years old. They have been run hard.

CONTROLLER - IMMEDIATE START 24-72V 25A

First time it happened was on a startup.
I unplugged and replugged all connections and then it started working normally. I was crusing along and it cut out. Cut out meaning it stopped engaging the wheel. The lights are on the throttle spins the motor, I can hear it, but not the wheel. Motor won't engage the wheel, not sure how else to describe it.

There is no chatter to speak of. It sounds slightly different when the motor spins in the hub without engaging the wheel but it's not a bad sound. The motor has no resistance so i hear it spin very fast in a short time.

On my way home when it happened I was riding along and it stopped spinning the wheel. Started pedaling home trying the throttle now and then. Then it engaged and worked for half mile, then stopped spinning the wheel again. It always spins the motor in the hub but won't always engage and spin the wheel.

Tried the reverse thing. No luck. Doesn't want to spin in reverse even when I spin it that way. I have anther controller I can try but plugs are all differnt so I'm gonna need to make some diy wire adapters.. O fun!

Thanks for all the help and ideas

I have taken it apart to remove some metal bits introduced when I used to long of screws installing the disk break on the hub. That was over a year ago. Been working fine Ever since..

 

[teklektik]

• The fact that there is always drag turning the wheel in reverse makes it sound like the clutch may be okay.
• The fact that this happens spontaneously while underway (not exclusively on power up) and 'cuts out' means 'stops engaging but motor keeps running' instead of 'motor stops turning' or 'controller turns off' makes it sound mechanical.
• The absence of chatter typical of clutch failure seems to point to some other failure...
• You still didn't say if the controller was sensorless or had a reverse switch capability, so any controller-initiated reverse rotation looks questionable.

In short: no smoking gun to point clearly to a failure. In fact - somewhat contradictory symptoms...

With another controller on hand I'd swap it in, but frankly it's probably a mechanical (clutch) issue even though the failure symptoms appear atypical.

It may be possible that some grease you used when re-assembling the motor after your cleanup of metal shards has contaminated the clutch. This seems like a very remote possibility but the symptoms of a 'greased slipping clutch' are almost exactly as you describe. Did you force any grease into the black plastic ring thingie in the gear cluster? Did you use the recommended MobileGrease 28 or some other more conveniently available grease?

 

[d8veh]

I think the probability of vlutch fsilure hoes right up whrn you menyion filings in the motor. It only takes one grain to compromise the clutch. It needs all three rollers to grip. One bit of dirt to jsm one roller and you're out. It's worth trying another controller just to be sure. It might even give it a faster jolt during start up to help the clutch grip.

 

[neptronix]

It's about 95% likely to be either the clutch or the gears.
Pop that baby open.

 

[teklektik]

I think the probability of vlutch fsilure hoes right up whrn you menyion filings in the motor.
...
It needs all three rollers to grip.

Agree it's likely the clutch - but BMC clutches have sprags not rollers - and there are a bunch of them...
Both old and new styles make it difficult for debris to enter the clutch. Not saying it's impossible, but the large aluminum flakes that split out from bottoming the brake screws have no reason jump in the tiny crevice in the assembly face - which typically has grease blocking the opening...

It is possible to extract the sprags and springs from the new style for cleaning, etc, but it's a bit tricky and there is no meaningful way to evaluate or refurbish the sprags or clutch facing. This goes directly to replacement as the repair option.

If the controller does not address the problem, there's not really any reason to open the motor until a replacement gear cluster is in hand since the clutch cannot be serviced - at least you can still ride a bit until the new one arrives and you can overlap the delivery time to get any necessary tools/supplies for the repair.

 

[Jsblastoff]

Thanks for everyone's help and thoughts!

I'll try my other controller. Then I'll look inside. Not gonna ride her till she's fixed. She's a heavy cruiser, with no power it's slowwww goin. And I have lots of hills around

I'll let y'all know what I learn

 

[jateureka]

When you hear the motor spinning, but there's no drive, there's three main possibilities. First, it might be going backwards. If you lift the wheel off the ground, it might turn slowly in the direction of the motor. Secondly, the clutch might not be engaging properly because avroller is stuck. Thirdly, broken teeth in the gears. You can normally hear that and it jumps a bit...

A fourth possibility is the press fit ring gear slipping inside the motor hub case. This happened on an old MAC motor that had a hard life and the slipping didn't normally happen until the motor warmed up a bit and expanded. I think Ypedal also had this happen on an early eZee hub motor and fixed it by drilling and pining the ring gear.

 

[teklektik]

A fourth possibility is the press fit ring gear slipping inside the motor hub case.

Whoa! That's a very interesting failure mode that exactly fits the symptoms.

Now there is very good reason to crack the case and take a look. Easy fix as well.
Good post.

 

[Skiyrround]

Just curious if you ever solved this one. Just happened to me today. Exactly all the same symptoms/characteristics. Any guidance is super appreciated. Thanks!

 

[pullin-gs]

The motor could be running BACKWARDS?
Check controller programming to make sure it did not auto-configure the motor to spin backwards.