Exchange 120mm BBSHD for 100mm (chainline concerns)?

[ColinC]

OK, so I'm doing a BBSHD build on a fatbike model with no prior builds for guidance. I measured carefully, posted some threads, got some advice, and ultimately decided the 120mm size was the 'best bet' due to concerns about clearing the chainstay. Good news is there's no issue with the chainstay (using just one narrow spacer on the drive side). Bad news is that I've got at least 15mm of unthreaded tube on the nondrive side. Don't the BBSHD lock rings need to butt dirtectly up against that bottom bracket to be secure, rather than butting up against spacers? Problem is if I put those spacers on the drive side I've got an even worse chainline situation. These pics show the chainline with my Luna Eclipse 36T front ring and chain on the 37T ring of my Shimano XT 11-46 rear cassette.

Should I exchange this 120mm for a 100mm? I assume I'd still have plenty of 'thread' on the nondrive side to tighten down everything correctly? Or maybe I'm wrong about being able to tighten the lock rings up against spacers on the nondrive side rather than directly up against the edge of the bottom bracket? Obviously my 'Q factor' or whatever would be lopsided to that nondrive side, but with the kind of off-road riding I do with this bike, I'm not thinking that would be an issue.


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[Fiddlerwill]

The lock nut needs to be next to the body to grip although luna has an extension torque bar . But maybe the spacers could go after the lock nut then the main nut ? I have a similar problem. I have the 120 kit to put on a 100 bb
There are 2,spacers frpm 100 to 120 forcthe 2 nuts right?

 

[ColinC]

I see what you're saying. Yes, that spider-looking bracket that bolts to the motor obviously has to go up against the BB. But then after that spacer(s) enough to reach the threads and then the two nuts. Not enough spacers in the Luna kit for this, however...I think I need to make my own from a single piece of pipe/cylinder...looks like the inner diameter needs to be about 1 1/4"...with enough wall thickness for that main lock nut to get a good "bite".

The lock nut needs to be next to the body to grip although luna has an extension torque bar . But maybe the spacers could go after the lock nut then the main nut ? I have a similar problem. I have the 120 kit to put on a 100 bb
There are 2,spacers frpm 100 to 120 forcthe 2 nuts right?

 

[Fiddlerwill]

Yes , that sounds like the best approach . Tell me , you have a steel or aluminium frame? Its possible with ‘A ‘ frames for a motor to tear out . Hence a torque bar could be a good investment, just to be sure