How to solve chain derailment on BBSHD and BBS02

[73Eldo]

Lekkie has a 42 or 46 with 18.3 so you would have to use spacers which I would think 4mm is pushing the limits. The Lekkie 40 can be 20.8, 18.3, or 15.8 depending on how you use the included spacer, not sure if you could us another spacer with the included one or not. How much threads you have left ? If you have 4mm there maybe sticking a BB spacer in and going with the Lekkie 42/46 would be the way to go?

[Ken Reich]

Currently i an running a 44 tooth 9 mm negative offset on my BBSHD trek caliber 7- would like to tidy up the chainline in lowest gear, are there any 12-14 mm negative offset rings out there? In 44 tooth?

[Dshue]

I know that I have my chainline written down somewhere but with these mid drives all that does is give you a reference to aim for. And if you get lucky you might hit it. But for the most part you just try to get as close as you can. I have found that on the two builds I have done with a BBSO2 (one with a 68mm bb and 7sp freewheel and one with a 73 mm bb and 8 sp cassette)that as long as you can get the drive side to clear and not use any spacers then the stock Bafang 44t chainring will give an acceptable chainline for 7 and 8 speed rear cassette/freewheel.

[Retrorockit]

I came across this which may offer a way forward. It looks like they used just the BB portion of a BBS including the pawl clutch. Without the gear case the chainrings can be smaller and sit in more. I could see this in the stoker position with 2 chainrings on it.
Another way if making your own parts is an option is to put a simple roller clutch in there. They look like and function as needle bearings but lock up in one direction. TSDZ2 uses one inside the drive pinion of the motor. With 2 riders and a BBSHD it would have to be a much higher torque capacity part than that one.
Actually the only torque through the roller clutch would be the 2nd riders out put. I have no experience with tandems so it takes me a while to get it straight in my head.

[Retrorockit]

They're going to be mechanically connnected anyway AFAIK. The driver is steering and should have the throttle . Simplifies the wiring. No photo of the front BB so I can't say. But the BB can probably be adapted. The rear suspension looks like there's no good solution there. I don't think offset 40t will help because the diameter will keep it from moving the chainline in anyway.

Oh I see no one way clutch between the stoker and the motor. The opposite of ghost pedaling I suppose.

[ncmired]

... mount the mid drive 'vertical' on it's own BB clamped or welded in the middle so the motor is not hanging under.. Still can go that way with an 02/750.

You mean, via a kid-back or child-stoker mount, maybe on the diagonal between the seat tubes? If so, you could probably use the bottle mount screws to help stabilize it. I'd then be concerned about clearing the chain through the shock/rear triangle gap - hard to visualize second-hand.

I considered using one of the stoker mounts to slow down the sky-high BBSHD cadence (2:1 chain rings) on one of my builds, but it just seemed like a mechanical mess especially if the motor broke down on the road.

[edllorca]

Retrorockit and Ncrkd Looking at a front mount indeed. Have to think through what the stoker will feel clipped in when the motor kicks hard. I do not have E-bike experience (except for 1 ride on a bbs01/250 that I built for my stokers single bike). Agreed that the bbs02/750 or even a pair of 01/350 is closer to doable than the bbshd. So much to consider. Ground clearnce has to be checked too before I venture in that direction. The genesis of this project when I bought the bike was to mount the mid drive 'vertical' on it's own BB clamped or welded in the middle so the motor is not hanging under.. Still can go that way with an 02/750.

As for where this bike will go the answer is, everywhere. Will build a second set of wheels with road rims/tires so one bike does it all with simple wheel changes.

[ncmired]

Dunno ... put a motor up front on a tandem, and hit the throttle - "Whoa Nelly!" goes the stoker. The frame also has a side-adjust eccentric BB on the front - another problem to tackle.

[Retrorockit]

My thinking is get 2 chainrings going on that rear BB and put the BBSHD in the front BB. 40T is the smalllest inset chainring. But the one you add in the middle doesn't have to be the same size. Probably should be if both riders want the same cadence, or if timing is a thing with tandem riders.

[ncmired]

Oh my ... you were hoping to run a dual chainring on the right, too (because of the BBSHD motor housing interference)?

Tandem, full suspension, mid drive ... yikes is all I can say. 73mm stoker BB? I'm thinking 750 watt BBS02B is a much better starting point with a standard left side timing chain setup, with the Lekkie 42T (or better the 40T) on the motor. Will the BBSHD vendor trade?

Are you riding road, gravel or dirt, down in the parks south? 30T to 40T is 6 gear inches (approx. 17 to 23), or 2MPH (6 to 8), at a cadence the BBS02 should be able to handle.

[edllorca]

Thanks for your interest fellas. Here are some shots. bike is a Ventana Conquistador. 73mm shell but unshaveable as the suspension linkage is right there. I don't think I need spacers for the BBSHD to clear the swing arm but I might as it is certainly right there with no spare space. The drivetrain is SRAM eagle GX 1x12 10-50T (not my choice) and is not rebuildable. The chainring is a 30 T at 50mm off of centerline. The chain line cant be any less or it will rub on the current 3" tires though I may go to skinnier tires. I included three pics, 1 on the lowest cog 1 on the highest and 1 where the chain is parallel to the frame centerline more or less and it lands on the 6th cog. According to my measurements the stock ring was at 63.5mm. I have not found out what the smallest chainring I can buy that envelops the final drive housing but I know if I go too large it will strain the chain too much for steep climbs.

So that is the story for the drive chain. The timing chain would have to move to the right side but that chainline is so bad too I suspect it will derail often and would probably wear gears out quickly

My latest thought is to run twin BBSXX 350W which lets me runs the timing chain on the left but I am not sure about the drive chainline yet with this scheme.

[Retrorockit]

Another suggestion for IGH chainline issues is to use narrow 8/9 speed chainrings, and narrow rear cogs so you can use the more flexible derailer 7/8/9 speed chains. These are designed to run out of line to a large extent. Not as strong but with proper lube and replacement schedule good enough for a BBSHD.

[ncmired]

Yep, a picture, along with what chain ring (28 or 36). If 36, would you be willing to go Lekkie 40, with a 45-46mm chain line (before spacers)?

Or lop the BB shell down as Retro mentioned, if you have the room.

Otherwise, you can only make your lowest current gear ratio functional by losing gears, as Paxtana said.

[Retrorockit]

Could you post a photo of the driveline so we can see how the tandem is set up. It will help avoid wasting time on suggestions that won't work.
I have cut down BB shells with a BB facing tool to be narrower on one side. Had my LBS do it. Said it was a PITA but worked. I also removed the gasket from under the drive side cover and used silicone sealer and gained another mm that way. Potentially this will get you down to 59mm chainline. Theoretically you could take a whole 5mm off of one side for an offset 68mm shell, and with no gasket hit about 57mm. I did the BB mod on a 73mm Trek TSDZ2 IGH project, and the gasket mod on a 73mm gary Fisher BBSHD. Didn't need to do both at once.

[paxtana]

Maybe you should look at reworking the cassette, as mentioned on this page