Hardy Boys Solve The Mystery Of The Nylon Gear Failure On The BBS02

In the past, I’ve told people when they replace the nylon gear (instructions are here) to use heavy axle grease on it as the Lithium grease that it ships with is incredibly light and tends to just spin-off the primary reduction gears when they are spinning at around thousands of RPM. After 5 minutes of Internet research, I’ve found that doing this is a terrible idea and can actually CAUSE your nylon gear to soften and fail prematurely (it was really a ploy to help sell more nylon gears for Bafang).

This takes me back to my original nylon gear failure about 6 months ago and I distinctly remember that the gear was 1/2 white (toward the motor) and 1/2 black grease (toward the drive unit) leading me to believe that this heavy axle grease had seeped through the bearing and possibly caused the nylon gear to soften and fail prematurely. For a video that proves my point check out this video from our favorite Aussie speed freak Bruno where he takes apart a BBS02 with 6000km on it. SPOILER ALERT : It has totally turned to the dark side.

Do I know for sure that this is what caused my failure? Absolutely not. Am I sure beyond a reasonable doubt? The more I research it, the more it looks to be true. The gear failed at high RPM under not-that-much load on a slight 5 degree grade hill going about 15mph in a very low gear. Considering how hard I usually thrash on my drive units there is no way this should have failed under those conditions.

IMAG2924

This is the nylon gear fresh out of the drive unit with the nasty black axle grease side facing up.

I’ve sorted through my photos of my nylon gear replacement and the more I look at them the more clear it seems to me that the axle grease is getting through the bearing. Is there any way to prevent this? When I lube up my secondary reduction gear on the other side I use a lot of black axle grease. Using too much grease and using the wrong kind might be allowing the grease to seep through the bearing.

In the future I plan on only using lithium (white) non-petroleum based grease on both the nylon gear side and the secondary reduction gear (axle) side. This way even if the grease seeps through the bearing it will not cause the nylon gear to fail. The grease I am going to use is Mobil Grease 28 which is safe with nylon and aluminum and should last about 10 years. You can get about 14oz online for ~$12 right here.

Clean this chamber out with a toothbrush, then clean off the toothbrush and carefully return it back to its owner without getting caught.

You can see the grease on the back side of the unit is a much darker grey color, almost black. It must have seeped through the bearing. Egads, that drive unit is FILTHY.

Will the BBSHD have a similar problem? It’s hard to tell, but from now on when I take it apart I’m not going to clean the black grease off the 2ndary reduction gear and replace it with my axle grease. I’m also going to be extra careful to never get any black grease in the nylon reduction gear. Use only white lithium grease when you have to replace this gear after failure. I found this very informative tidbit by “callpocket” on this post here.

Back several years ago when I rebuilt a few VCR machines, all the manuals had big notes written in red telling the techs to only use white lithium grease to lubricate the plastic gears because petroleum grease would cause damage to the gears. I found this to be the case also (from experience) to use this white lithium grease on the plastic or nylon rollers used in window mechanisms for many older vehicles. Owners and shade tree mechanics had used vaseline or axel grease to lube these and the nylon or plastic rollers came apart. I always replaced them and used the white lithium after I saw the damage from the other lubricants.

Makes me hungry just looking at it.

The side of the nylon gear that faces the rotor is almost entirely Lithium grease. It does kind of look like a VCR gear.

Thanks to Dieter Spiller for pointing out the blatantly obvious to me. I told him to use KY Sex Lube in his Nylon gear and he rightly refused to. If only everyone was smart enough to ignore my great advice. There is a special place in hell for people who use petroleum-based grease on their nylon gears, and I’ve already got my one-way ticket.

Ride On.

19 thoughts on “Hardy Boys Solve The Mystery Of The Nylon Gear Failure On The BBS02

  1. I’ve had good luck in the past using automobile high-temp synthetic disc brake axle bearing grease on a wide variety of jobs. I wonder if it would work on the type of plastic in these gears? Google: “Typically, lubricants based on silicone, PFAE (perflourinated), most synthetic hydrocarbons (SHC or PAO), or mineral oils work well with plastic gears. Lubricants based on esters or polyglycols are generally not compatible with plastics”. Also, do we know that the gears are definitely nylon? or has that been assumed?

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  2. Great article and entertaining as always, Karl! The more I think about this whole grease issue, the solution might be to get somebody like Eric or Paul who seem to have good relationships with Bafang to start supplying the different greases as repair parts along with the gears. Or, if that is not possible, at least get Bafang to clarify and recommend appropriate compatible greases that can be sourced locally.

    I have had some issues with a new BBSO2 750W motor becoming noisier after only 200 km of light use. Inspection revealed that a minimal amount of light, white grease was used on the metal reduction gears instead of the typical heavier black grease seen in most disassembly videos. That raises the question – did Bafang recently change to a lighter, lithium grease because they have concerns about nylon gear deterioration? Somebody else recently posted a video on Endless Sphere about a very similar situation with a new 750W motor where only a minimal amount of white grease had been applied. Makes you wonder what’s going on?

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    • When I took apart the BBSHD it had white grease in the nylon gear and black grease on the axle side. It had very little black grease. I’m thinking a lot of lithium grease on the big gears is the way to go. That is what I plan to do from now on.

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  3. Generally speaking, nylon gears require no grease, they are self-lubricating.. That, in fact, is the reason nylon gears are designed into the unit. If the unit was designed to run with grease then a steel or bronze gear would have been used. The unit would be able to handle more torque, but require more maintenance.

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  4. I think that when Bafang designed their bicycle motors they built in a few failsafes. The nylon reduction gear is one of them. It will fail before other parts in the motor will because it was designed to do that. Sure, the introduction of incorrect lubricants will speed the process by breaking down the nylon. Nevertheless, the motor will continue to fail in that specific place until you upgrade the material used for the reduction gear. And then it would fail somewhere else that may not be so easy to repair.

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  5. After some diligent browsing, I think I may have found a grease that appears to match all the required criteria: GENUINE DOW CORNING MOLYKOTE EM-30L Full Synthetic Polyalphaolefin (PAO) Base Lubricating Grease w/PTFE, Developed Especially for Plastic Components. It is a high-performance white synthetic grease with solid lubricants for extreme pressure, for use with plastic/plastic, plastic/metal, plastic/rubber and rubber/metal combinations involving slow and medium-fast movements and medium to heavy loads. White Color. NLGI #1.

    APPLICATIONS:
    – Suitable for lubrication points with medium to heavy loads and low to medium speeds.
    – Switches: Lubrication of plastics and electrical contact.
    – Actuators: Lubrication at wide temperature and various materials.
    – Micro Motors: Lubrication at wide temperature and various materials.

    TEMPERATURE RANGE: From -49ºF to 302ºF (-45ºC to +150ºC)

    SOLVES THESE LUBRICATION PROBLEMS:
    – Plastic Gear Wheels in Enclosed Gears
    – High wear and short life owing to high temperatures or heavy loads.
    – Swelling, range shrinking, stress cracks, change in strength characteristics due to inadequate lubricant.

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  6. Pingback: Mobilgrease 28 & BBSHD/BBS02 : Because A Good Mid-drive Is Better Seen And Not Heard | Electric-FatBike.com

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  9. I used black moly grease on secondary reduction gear within 30 days the internal plastic gears we’re basically disintegrated is the mobile 26best for secondary gear?

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