Bafang Ultra RH crank arm - Resolved

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Guys, new issue starting on my fairly new Ultra powered Rize RX Pro at 150 miles or so. The RH crank arm is making noise, and when checked, the attaching bolt will be loose. When tightened, it will start making noise again within just a few miles. I've marked the bolt to see if it was unscrewing and it is not. This has to be a failure of some sort. At about 175 miles, I've tightened it 4 times, and this last ride it only made it a couple of miles before starting the clicking again.

Tonight I've done some homework, and it appears that this is not the first time the problem has surfaced. Less clear is the permanent solution. I can buy replacement Bafang (or more likley, knock offs) crank arms on Amazon, but the question is, will I be throwing good money after bad?

Thomas offered an opinion regarding Lekkie Buzz Bars in a post a few years ago. I located a set of those at EM3EV, but they're 90 bucks (Amazon was 22.)!

Any experience you'd like to share?

Thanks! -Al
 
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linklemming

Well-Known Member
Well the good news is there is a ton of ISIS crankarms available, the only issue will be finding the correct offset/q-factor.

Im confused how its getting loose if the bolt isnt coming loose unless they are just cr$p arms.

Easiest first thing would be to get a set of bafang arms from a known bafang dealer (i.e. california e-bike) and make sure to torque them down to proper specs.
 

smorgasbord

Well-Known Member
Region
USA
The first thing I'd do is remove the crank - if you can - then clean everything and then apply grease to the splined shaft and inside the crank arm. Then tighten the crank bolt to the specified torque (use a torque wrench!).

If that doesn't help, then there may be a mating problem. @harryS 's suggestion of using shims is interesting, but feels somewhat problematic to implement to me. The question would be whether the splined shaft of the crank arm hole is machined incorrectly, and how to best compensate or replace. But yes, some kind of very thin yet durable shim might be able to be inserted to stop the crank arm from "bottoming out" before the proper tension is achieved.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
An update for anyone curious. The Ultra motor use an ISIS type crank, kind of a course spline with 6 or 8 teeth maybe. It is NOT the square or diamond taper you see more commonly used on crank arms. Until taking this thing apart, I'd never seen this setup.

So let me ask those that might be more familiar with this design a question. Is this RH crank arm supposed to draw down on some sort of taper built into these splines, or is it supposed to draw down on the E-clip located just inside the arm - like mine is doing? I'm very suspicious of the idea that even though the crank end of the arm appears very beefy, it's stretched or was machined incorrectly to start with.

I had it all apart, cleaned it and gave it a close inspection. There are no visible cracks, and no "fretting" apparent anywhere, indicating something is moving around, 2 parts working on each other. So I lubed it all up with grease (including the bolt threads), and reassembled, setting the bolt with 40nm of torque. 2 miles later it's clicking again.

BTW, this is a 4" fat bike, and the arms have 30mm offset - probably adding to the stress placed on the crank arm. -Al
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Sourcing 30mm offset ISIS crank arms is proving to be a challenge. Need the 30mm offset for fat tire clearance.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
As it turns out, it was the seat making the noise. Not the crank arms as I had suspected.

I shifted my weight just right on a ride today and noticed a noise similar to the clicking I had been hearing when pedaling. So I REALLY shifted my weight, the seat let out with a big squawk, and then silence. The clicking was gone! Back to the big grin I was riding with prior to the clicking.

How frustrating! Geez, I'll bet it took me 10 rides and that many hours of going over nuts and bolts, installing zerk fittings into the pedals, etc. All due to a stupid click coming from the seat.

Will now look into the source of the noise in the seat and eliminate that.

Silence IS golden! -Al
 

theemartymac

Active Member
What are you running for a seat? I have a cheaper Daway spring cruiser seat that clicked whenever my weight shifted as well. Seems the problem was the double spring system was rubbing together at the ends of my pedal stroke. I swapped it for a spring/elastomer Serfas E-Gel because it was a nice upgrade anyway, and I was too lazy to mod the other one. Mom's ebike got it.

And just an FYI, I did have recurring loose cranks on my Rize X with the 750 Bafang hub drive. Had to overtorque a little to get it to finally stop, but it's been fine for 800+ kms now.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
This is the seat. It's one of those oversize seats that are supposed to support you a bit better, though the jury is still out on that. I don't remember seeing a lot of metal underneath it, but I haven't looked closely with this noise in mind. That'll be happening soon.


I've used Cloud 9 seats extensively in the past - and they're always creaky. One of the reasons I was looking for something different. -Al
 

theemartymac

Active Member
If you want to try a new one, I can't speak highly enough about the Serfas Cruiser line, or the E Gel line. Love them immensely. Comfy and quiet. I use a super cruiser on my hub bike, and an E-gel Cruiser on my ultra-mid.

But before sinking new money in, those wings scream "easy leverage" to me. I would take the time to disassemble and clean all the clamping surfaces including the rails, tube, seat clamp, etc, and reassemble with some anti seize or assembly lube to a decent/proper torque spec. Could be as simple as less than ideal surface seating and torques.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
We're not only the same size, we think an awful lot alike. Thanks for the new seat ideas. -Al