Bafang bbs02 / bent frame

[bono]

Hi,

My Bafang bbs02 is in service now (was making funny noises), so I could take better photos. As you see, the motor damaged the frame.

Is it because of incorrect mounting? What should I do to stop this when I install the motor back? Should I install some kind of metal plate between the frame and the motor?

thanks!

 

[opperpanter]

Are you sure you didn't hit anything with the motor, which also damaged the frame?

 

[friendly1uk]

install the motor back?

I wouldn't

 

[Arvicola Terrestris]

My guess is you have hit something, there shouldn't be enough moment in the motor to damage steel like that. Maybe if the motor is completely loose, and can accelerate around it's axis, before hitting the frame.

But your damage is much more fun to tell about then my crank shaft bearing problem :wink:

/philip

EDIT; now I see your frame is aluminium, but anyway sounds unlikely without some outside force.

 

[2old]

Aluminum is somewhat notch sensitive and that crack could precipitate catastrophic failure. I would trash that frame. You could weld the area, but might need some form of heat treatment afterward.

 

[bono]

I am 100% sure I did not hit anything. I believe the motor could have been a bit loose... So you think this is a serious damage? I am using the bike only on flat terrain, no jumps, etc.

 

[Arvicola Terrestris]

I am 100% sure I did not hit anything. I believe the motor could have been a bit loose... So you think this is a serious damage? I am using the bike only on flat terrain, no jumps, etc.

Okay if the motor has been loose AND the frame is aluminium, accepted.

Your frame is then probably an aluminium alloy called 6061-T6, which means it is very easy to weld (if you can weld aluminium). BUT the "T6" means that it is hardened by heat treatment AFTER the frame is welded to make the frame inclusive the welds MUCH stronger.

If you heat the aluminium now, by welding, the hardening of the frame and welds will disappear asap. You can't heat treat the frame yourself, unless you have access to an 300 degree Celsius oven the frame fits into.

So if you weld this damage you will get your bike on the road again but the lower part of your bike will be weak. The problem with aluminium is that it breaks quite fast, it snaps. Unlike steel frames like unhardened Chromium Molybdenum steel used for BMX-bikes which has 3x higher fatigue strength then 6061-T6.

That is the downside of aluminium bike frames, so my answar is: New frame :?

/philip

 

[samsavvas]

Hi,

My Bafang bbs02 is in service now (was making funny noises), so I could take better photos. As you see, the motor damaged the frame.

Is it because of incorrect mounting? What should I do to stop this when I install the motor back? Should I install some kind of metal plate between the frame and the motor?

thanks!

It would be impossible for the BBSxx unit to do that sort of damage unless you had it quite incorrectly mounted, most likely with inadequate tension on the 2 large threaded BB nuts and/or on the left-side mounting plate screws. These two parts of the mounting system operate together to stop the drive rotating around the axis of the BB and to prevent it twisting in line with the frame. The unilateral (left-biased) site of the damage to the lower surface of your down tube and the forward edge of the BB tube suggests to me that:
- the drive has been quite loose in the BB tube, allowing it to rotate around the BB with considerable force
- the heavy mass of the motor has been able to actually twist back and forth with respect to the longitudinal (fore-and-aft) axis of the bike - hence the damage to the down tube on the left side.

There are clear instructions available for mounting the motor, available in pdf form from most vendors. The motor should be snugged up tight against the lower surface of the down tube and should not be moving around the BB axis at all when under use. Use a proper BB hook spanner for the first notched M33 lock ring and then (if you have one) a notched BB ring spanner for the second lock ring (if you have the later version that has a hollow, 'wrap around' lock ring rather than a second notched ring, which just requires the hook spanner). Make sure that the 2 M6 screws that bolt the left-side mounting plate to the motor are tightened to the appropriate torque. I'd put some loctite on them given your past experiences. Also make sure that you have this mounting plate properly aligned - the small protruding bumps around the BB hole on one surface of this plate should face and engage with the end of the BB tube, not the other way!

As others have pointed out, you have an aluminium frame. It's probably heat treated and this dent and crack should be regarded as severe damage to a vulnerable and high-stress part of the frame. Unless you are just pootling to the shops or school and back and never standing on the pedals, it's my own view that you should ditch the frame (metal recycling bin) and find yourself a replacement. My personal (and quite biased) advice would be to find a suitable cro-moly bike or frame - new or second hand, it doesn't matter - in the bike style you are after and with a 68mm BB width, which is what the BBSxx is really designed for. A good cro-mo frame will make a relatively light e-bike and most importantly, it won't let you down or add unnecessary complexity. I know we think of aluminium as 'lighter' but mostly, by the time you turn it into a bike frame, especially one with rear suspension, it ends up the same weight as steel (or heavier)! People have installed the BBSxx onto super-light weight alloy and carbon frames, but I'd leave this to the engineers (and artists) amongst us!

Make sure you follow the instructions when reassembling the drive and get some informed advice from someone with mechanical experience if you feel you are not up to it. I don't mean this to sound presumptuous or like a put down at all, but please remember, a bike is a highly-developed road-going vehicle and your welfare may well be at stake if something goes wrong at speed. What very often doesn't come across in these discussions at ES is the high degree of care and consideration for safety that more experienced DIY home bike mechanics and e-bike riders put into their bike maintenance and assembly. Bikes are not toys and have some complexities of their own that may not be obvious to the inexperienced user. Adding an electric drive can make things even more complex. It seems that most DIY e-bikers - those that don't have engineering training anyway - make plenty of mistakes when starting out. The trick is to make sure that we learn from them. The great value of this ES forum is that we can all learn from (and build on) eachother's mistakes and experiences!

Ride safe,

Savvas.

 

[bono]

Thank you guys! A lot of good, valuable information. I think I will buy a new bike to install the motor (I am doing 25 miles every day on the bike) and I will keep the old one for a shorter, local trips. I will be looking whether the dent is getting bigger. Do you think that such dent could result in a sudden collapse of the frame or it would be creaking gradually?

In relation to the motor mount - somebody from this forum was helping me. I am not an expert in such stuff. Apparently, this installation was not perfect...

Thanks again!

 

[--freeride--]

Is the frame cracked on the outside of the dent?

if it is cracked, i would drill small holes at the ends of the crack, to stop the groth of the crack. Allthough I would glu a 5mm aluminum plate on the downtube the way that the motor can put pressure on that plate.

You got a dent there because your downtube is very wide and the nose with the thread from the motor is suposed to pas by the downtube. I did grind the edge of that nose away, so that Motor could swing up with the rubber against the downtube. At your frame that won't work because the downtube is to wide.

 

[bono]

Well, it is cracked by the dent (see the first photo) or you are asking about something else...

I have research a little bit for a replacement.

Diamondback Overdrive Sport 29er http://www.amazon.com/Diamondback-Bicycles-Overdrive-Mountain-29-Inch/dp/B00FFUAV90

I am not sure about the bottom bracket size - need to call a shop later this morning. However, I understand that even if it is 73 mm, it is workable solution? Do I need a piece of hardware to make the motor fit? How much is it? If it is expensive, I will buy similar bike I have now (68 mm) as I do not want to invest to much.

Thanks!

 

[2old]

Why not consider a frame (either aluminum or steel) from Bike Nashbar ($99, but frequently 20% off). I have purchased both, the aluminum for my wife and the steel as a platform for a 1000w ebike for myself. The bottom brackets on both were 68mm, so no problem there, and you could just transfer the components from your broken frame (didn't check your wheel size, but they have 29er and road frames for the same price). Before anyone asks, I'm not affiliated in any way with them, but have purchased many great productsfrom them.

 

[friendly1uk]

The damaged area is under tension. It holds perhaps half your weight, as you bounce around. The tube was probably round and squashed that shape at the bike factory. Weakening it where corners were formed, as shown by the rip. The tube is much more likely to fail in one go than bend to another shape and still be able to support you. I just can't imagine that happening at all. Failure will be a painful experience. Many members here wouldn't get to the shops once on it.

Remember they don't use any more material than they need to, and the strength that tubes bring has gone. Leaving a tearing edge. You got off this bike in time this time, but I wouldn't risk another go.

 

[sculptingman]

Aluminum frames can be problematic. The Bafang needs to be held as tight to the downtube as possible when you torque down the clamp that holds in in place... This clamp is steel and has raised ridges that are MEANT to dimple the Edge of the Bottom bracket, so that the Bafang won't shift position.... However... It's a steel clamp designed to crimp a steel BB.
Aluminum is soft enough that the sheer weight of the motor, when riding over bumps, can cause the clamp to gouge wider dimples in the BB... Which allows the motor to drop slightly away from the downtube... A sudden application of power...and the motor forcefully counter-rotates to smack against the down tube.

The next bump when power is off and the motor drops away from the tube...only to smack against it again under power...

In this way the Bafang can literally HAMMER an aluminum down tube to pieces.

So, number one... When installing on an aluminum frame, make sure the clamp is tight and check it frequently to make sure it stays tight.

Secondly... Improve the mating of the motor to the downtube. On my Spot Ajax, I sculpted a piece of epoxy clay to create a thin wedge shaped spacer between the Bafang motor and the downtube. It matched the contour of the tube... And fit against the rubber pad on the Bafang that is the motors' intended thrust bearing surface. In this way I was able to modify the thrust against the downtube to be more evenly distributed over a much wider area of aluminum tube...

Lastly... If you still find play in the motor... It's time to macgyver some zip ties into a Clamp, to hold the motor securely against the down tube... With perhaps an elastic spacer between motor and downtube.

 

[sculptingman]

PS- you can also run the controler cable between the motor housing and the BB... And folks also sometimes see this controller cable get damaged by the motor whacking against it repeatedly.

In the previous post I suggest modeling an epoxy putty spacer to spread the load between motor and downtube... Well, if you do this cleverly, you can model this spacer with channels in it that will allow you to guide controller, brake and shifter cables under the down tube, between the motor housing and the bottom bracket.... And yet prevent the motor from pinching the cables.

 

[mfj197]

Sculptingman, that's good information - thanks. I'm putting a BBS01 on an aluminium bike at the moment and like the idea of the epoxy clay so will go looking for something like that.

Michael

 

[Marc S.]

As a mechanic with a little background in aeronautics and three broken high quality aluminium frames under my belt, I'd say that frame is trash.
I wouldn't even use that thing for short trips anymore.

 

[speedmd]

Rather than throw it out, I would attempt bonding a well formed aluminum cap over the entire area and see how it goes for a few weeks. It is toast unless welded / repaired otherwise. Sand the paint away, peen down the sharp edges, and stick down a 1mm thick aluminum section, and overlap the damaged areas a good inch in all directions. Ugly, but should hold if its cleaned /prepped and clamped down tight while curing. You could also use fiberglass / carbon fiber /epoxy. Pile it on/ ride on!

 

[bono]

Thanks guys! This very helpful. I have ordered a new bike. Now I am riding without the motor and checking whether the creak is getting bigger. I know, I am risking, but I do not have much time to fix it properly. I will probably buy a new frame or will try the solution suggested by speedmd.

Sculptingman - please could you post a photo of the wedge shaped spacer you created? I am not that handy, so I would appreciate a little bit more guidance... As an alternative I was thinking about mounting a steel plate between the motor and the down tube. The solution with the epoxy clay spacer would look definitely much better.

thank you!

 

[sculptingman]

Here's a shot of my Bafang where it meets the downtube. The Ajax had an existing boss for a cable guide in this location, so I designed the Spacer to attach with a countersunk screw at this location... You can see that the spacer fits the contour of the down tube, and rests against the entire rubber pad surface on the Bafang... You can also see that I took advantage of the gap between the Bafang motor and the BB shell to rout the shifter/brake cable, and the controller cable under the BB... I sculpted the spacer to allow channels for these cables that would prevent the motor from pinching or impacting the cables.

 

[sculptingman]

Despite this,,because of the softness of aluminum versus the Bafang's iffy steel clamp design... The motor still works it's way loose over time and I need to regularly tighten it. For this reason, I am currently designing a similar, tightly fitting thrust spacer that will wedge between the Bafang motor housing, and the adjacent pletscher kickstand base.

In the photo here you can see that I currently use the pletscher to neatly wrap excess cable around... The spacer I am designing will allow for a neat cable layout... Yet press against the motor from the 'gravity' side to help isolate the motor and hold it more firmly against the down tube spacer. Transferring that load thru the kickstand body and into the kickstand plate...which should take the loading without issue.

 

[sculptingman]

To make one... First, set your frame upside down in a repair stand... Or however you can.

Loosen the Bafang if it's already tightened. You want to either apply Vaseline to the surface of the downtube... And the Bafang's rubber thrust plate... Or cover one or both surfaces with Saran wrap.

Model the putty in places... If you are routing cables as I did... Then you either want the cables Under the Saran wrap...or well greased... But before applying grease or plastic wrap... Use some oil based modeling clay ( plastilene ) to Fill in the under part of the cables so that the Putty can not wrap AROUND them...making it so you can't get the spacer off the cable ... ( in other words...make sure the profile of the cables are DRAFTED like the tapering shape of a paper cup )

Apply the epoxy putty and simply pull the Bafang to squeeze the putty against the downtube... If the bike is upside down, the weight of the motor will hold it in place until the putty cures... But while you still can, use a sculpting tool or whatever to reach around the putty spacer and press it firmly in place... Make it fairly smooth and control the shape.

if there is a cable guide boss... Like on mine... Then insert a longer version of the same type screw-- with its exposed threads filled vp with Vaseline or plastilene...and shape the putty around the screw to form a custom bolt hole. If not... Then make sure to sculpt a feature in the putty that will allow you to attach it firmly to the frame...like with a zip tie... Or, you could pull off the rubber pad on the Bafang... And mold the putty spacer to fill that spot...glueing it in place on the Bafang when the spacer is finished.

Once the putty has fully set... Remove it...clean up your bike... And use an ordinary File and sandpaper to dress up the edges of the spacer to look sharp. Some puttys come in colors you might like... Or you can paint the resulting part before Installation.

I will be doing a similar process to create the wedge spacer I intend to place between the motor and kickstand.

 

[bono]

sculptingman - MANY thanks! and wow - everything look like band new... I should care a bit more about my equipment.

Is my understanding correct that you attach the spacer with a countersunk screw directly to the frame? Can you drill the frame? Does it make the frame weaker? The rubber pad on the Bafang you mentioned - is this something what came with your motor? I did not have it?

 

[friendly1uk]

Sculptingman, that's good information - thanks. I'm putting a BBS01 on an aluminium bike at the moment and like the idea of the epoxy clay so will go looking for something like that.

Michael

I don't think you will do any better than this http://www.ebay.co.uk/itm/Milliput-Standard-Grade-Yellow-Grey-Cheapest-On-Ebay-Freshly-Made-/111539641849?pt=UK_Crafts_Cardmaking_Scrapbooking_Glue_Tape_EH&hash=item19f847ddf9

I like that A & B are mixed equally, allowing me to mix up very small quantities.
You could make a marble sized ball and squish it in place. Oil or clingfilm the motor and frame so the stuff don't stick. Remove your part once set, and cut away the edges to square it up.

You could forget the barriers and just glue the motor in place with the stuff. You may loose some paint, but it's not great at gluing things together. It's not wet enough. To really join things you want to massage a bit of freshly mixed stuff on to the surface. Make it smear. Then your golden. If it fails after that, it's perfectly fitting shape will aid another adhesive holding it in place.

Factory direct so it's nice a cheap. It's one of our better products. Something similar is £10 so it is well worth having. Comes in a range of colours. The white is hardest to mix as both parts are white.

It's one of my better discovery's. From a jeweler.

 

[sculptingman]

sculptingman - MANY thanks! and wow - everything look like band new... I should care a bit more about my equipment.

Is my understanding correct that you attach the spacer with a countersunk screw directly to the frame? Can you drill the frame? Does it make the frame weaker? The rubber pad on the Bafang you mentioned - is this something what came with your motor? I did not have it?

Well... First of all... I sure hope you did not think I was recommending epoxy putty to 'repair' your cracked frame... The damage shown in your photos can not be fixed with anything short of stripping the paint and TIG welding new aluminum.

The epoxy trick is a way to fairly quickly make add on parts... In this case, Custom molded spacers meant to offer a more even distribution of loads... Or cable clamps... Things of that sort. The advice was intended for whatever frame you get to REPLACE the damaged one. ( tho...if you get the frame properly welded... You could make a custom spacer to improve the contact between repaired frame and Bafang. )
Do not rely on epoxy to fix metal tubing... Especially not at a high stress location like the attachment of the down tube yo the BB.

Your frame , as shown in The photos is NOT safe to ride. Especially not with a 750 watt motor which can DOUBLE the torque you apply to the driveline.... And a down tube separation at speed is a potentially FATAL accident. So PLEASE... Do not ride that Frame ( sorry I didn't mention it in my posts, but I thought the previous posters had pretty well covered that the damaged frame is unsafe )

The rubber pad is on a flat spot on the motor housing... The flat spot that contacts the frame when you swing the motor up Against the downtube. Look and see if there is an obvious spot where it USED to be...it may have fallen off since its only held in place by glue. ( or perhaps you have an older model Bafang... And they added this feature because of the motor doing damage to frames like yours )
If it's not there... And you are making a spacer out of putty.. You can try adding one... Any self adhesive rubber material that you can cut to shape should work... Or, you can coat the putty spacer you make with Vinyl ( you can find cans of liquid vinyl for dipping tool handles in to make vinyl grips at most any hardware store ). OR... If Adventist, Make your spacer, itself, out of an elastomeric compound, There are silicone rubber puttys you can order online...