Technical > Transmission
BUILDING AN ELECTRIC BICYCLE AKA PEDELEC
Andre Jute:
Here we have a Bafang 8FUN QSWXK motor leaking oil.
What do you reckon. Should I panic? Rebuild it -- the dedicated tool is pretty expensive? Ignore it?
All input welcome.
Andre Jute
Danneaux:
Wahohhhhh. Wow.
Andre, based on my own experience, I would figure one or more of the following have occurred:
1) The motor has overheated, likely through some increase in resistance of an internal component, perhaps in a field winding or an internal lead, thus leading to elevated temperatures and lubricant migration.
2) A seal has given way, allowing lubrication to escape.
3) Both 1) and 2) above.
I take it all the side-plates are stationary wrt to the axle until we reach the interface that is leaking oil?
Aside from the leak, is performance as before and as expected?
This looks Big. And Bad.
Is it under warranty? Why would you need to rebuild it or invest in tools if it is?
Best,
Dan.
Danneaux:
Andre,
Giving it further thought and looking again at the assembly diagram on your website ( http://coolmainpress.com/BICYCLINGbuildingpedelec1.html ), I think more than ever the grease you see is the result of excess temperatures cooking the grease in the motor's bearings, rather than any grease present where the plastic gears are housed.
I've seen a very similar-looking exudate coming from the dust shields on kitchen and bathroom fans as well as an older attic fan. The culrit in each of those cases was prolonged, excessive heat causing the grease to break down and go beyond its temperature rating. The result? It could no longer be contained behind seal tolerances designed for a higher viscosity.
I hope this is not the case for your unit, Andre, but if the hub is still operable, I would be interested to see if it becomes warm or hot after a typical period of your use (be careful; you don't want to burn a finger). That assembly shows the hub shell serving as a heat sink and there are no cooling fins; the thing probably depends on airflow from normal forward movement and the heat-dissipating qualities of aluminum to cool the motor.
My second guess -- also prompted by a close look at the diagram -- is a slipping clutch as a source of overheating, also causing loss of lubricant.
Or, it could be they just over-packed the hub with grease or left off a seal. You're going to have to fix it; to leave it spewing oil is not only antithetical to your values and the bike it is mounted to, it is Anti-Andre. I think ignoring it is "out" for the same reasons. What if the internal gears are grinding themselves to bits, even silently? Y'gotta know. Heck, I'm dying to know how this comes out, so please let us know what you find if you disassemble it and how it progresses to conclusion. Photos would be good. All part of your documented experience with the hub to date.
I'm sorry you're having problems with it; such a pity.
Best,
Dan.
Andre Jute:
I'm not overly concerned, Dan. I bought that electric motor kit for an inexpensive experiment, and I live in atrociously hilly countryside, and weigh pretty near the stated limit. My Rohloff when I first got it leaked enough to form a puddle on the floor, and members here had to talk me through a black mood, but it came to no harm. Surprisingly, the electric motor is one of the cheaper parts of the kit. A Rohloff costs a thousand Euro and then some to replace, an electric motor built into a rim about a quarter of that after carriage, import duties, and taxes are added on.
This may be a hint that I should order that BPM high-torque motor I've been lusting after...
I'll send that photo to the suppliers and see what they say. We'll take it up again when I've heard from them.
Andre Jute
Andre Jute:
--- Quote from: Hobbes on July 18, 2012, 11:01:11 pm ---I'm not overly concerned, Dan. I bought that electric motor kit for an inexpensive experiment, and I live in atrociously hilly countryside, and weigh pretty near the stated limit. My Rohloff when I first got it leaked enough to form a puddle on the floor, and members here had to talk me through a black mood, but it came to no harm. Surprisingly, the electric motor is one of the cheaper parts of the kit. A Rohloff costs a thousand Euro and then some to replace, an electric motor built into a rim about a quarter of that after carriage, import duties, and taxes are added on.
This may be a hint that I should order that BPM high-torque motor I've been lusting after...
I'll send that photo to the suppliers and see what they say. We'll take it up again when I've heard from them.
Andre Jute
--- End quote ---
Today I cleanded up that hub and discovered the outlet for the oil, a breather hole of under 2mm in the thin edge of one of the ridges on the hub.
I've been using the bike meanwhile and noticed no great increase in the concentration of oily matter, and there probably was none, and the small breathing hole seems clogged. There is no degradation of the motor's function.
This I read as partial confirmation of a suspicion that has been growing with thought. On the two really warm day this summer, I rode to Kilmacsimon Quay and uniquely didn't return on the flat, but up two steep, long hills, about 100m elevation in each case.
It seems to me possible to likely that some hefty quality of grease inside the hub was thinned enough by heat to leak through the breather, and then recovered its viscosity and blocked the breather.
I'm therefore going to do nothing -- always a good course when you don't have enough facts! -- and see what happens.
The question is, should I open the breather hole, with a toothpick, say? Or not?
Andre Jute
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