Bafang Ultra RH crank arm - Resolved

[AHicks]

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

 

[linklemming]

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.

 

[harryS]

I'd cut some shims out of a aluminum can, and see if that holds the pedal on tight.

 

[smorgasbord]

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.

 

[D.Unwin]

Lekkie Buzz Bar offset crank arms (pair)

Lekkie Buzz Bar offset cranks for Bafang BBS01/02/HD motors. Precision CNC machined and a cut above the rest.

www.brightonebikes.co.uk

 

[MartsEbike]

Maybe check the threads... Possibly over-tightened at some point?

 

[AHicks]

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]

Sourcing 30mm offset ISIS crank arms is proving to be a challenge. Need the 30mm offset for fat tire clearance.

 

[AHicks]

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]

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]

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.

Amazon.com

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]

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]

We're not only the same size, we think an awful lot alike. Thanks for the new seat ideas. -Al

 

[Escoozeh]

Did you ever find after market crank arms anyways? I have a Frey Hunter (M620 + 26x4.5" tires) and am trying to get some shorter crank arms. I just have no idea what to make of q-factor and the required measurements. Biketrix and Backou both sell 150mm crank arms and I know they make very similar fat bikes so I'm tempted to just pick those up but I want to make sure I get the right size

 

[greeno]

Miranda is a good source for crank arms I have purchased from them in the past. There over in the UK so a weeks wait for those to show up and they don't stock the 160mm size that I prefer.
Another company is up in Santa Cruz Cal. and they are called PRAXIS.
They make the 160's that I like using and their E-cranks have the correct "Q" factor that I need for my Ultra motor and Exess frame.
Shimano makes cranks but they might not offset enough for a bafang motor.

Whatever you do make sure they don't interfere with your rear chainstay.

My cranks have almost an inch clearance from the crank arm to my chainstay.

I think the cranks were like $70. Great quality and good customer service to boot.
Good luck.

 

[Escoozeh]

Miranda is a good source for crank arms I have purchased from them in the past. There over in the UK so a weeks wait for those to show up and they don't stock the 160mm size that I prefer.
Another company is up in Santa Cruz Cal. and they are called PRAXIS.
They make the 160's that I like using and their E-cranks have the correct "Q" factor that I need for my Ultra motor and Exess frame.
Shimano makes cranks but they might not offset enough for a bafang motor.

Whatever you do make sure they don't interfere with your rear chainstay.

My cranks have almost an inch clearance from the crank arm to my chainstay.

I think the cranks were like $70. Great quality and good customer service to boot.
Good luck.

I'm a bit confused as to how I can make sure they clear. I know it has something to do with the q-factor. Can you explain or give me a guide as to how I can measure to make sure

 

[greeno]

Sure sure.
Q Factor is the distance between the outside of one crank arm to the outside of the other crank arm.
How much offset outward from the crank bolt to spin free of the motor as well as not hitting your rear chain stay ( lower rear frame support the cradles the rear wheel.
The last Pair I got from Praxxis was Bosch/Yam 160mm Alloy E-Cranks.

Google is your friend.

Type in pedalchile.com What is q factor on a bike.
Select Q Factor Explained 7 pictures.
And now your Bob's Uncle.

 

[Escoozeh]

Sure sure.
Q Factor is the distance between the outside of one crank arm to the outside of the other crank arm.
How much offset outward from the crank bolt to spin free of the motor as well as not hitting your rear chain stay ( lower rear frame support the cradles the rear wheel.
The last Pair I got from Praxxis was Bosch/Yam 160mm Alloy E-Cranks.

Google is your friend.

Type in pedalchile.com What is q factor on a bike.
Select Q Factor Explained 7 pictures.
And now your Bob's Uncle.

So is finding the correct crank arms just a matter of measuring the distance been the outside of one crank to the outside of the other?

I was a bit confused because I've seen q-factor referred to as q0 pr q16. It makes more sense if it's simply the mm distance been the outside of each crank arm

 

[greeno]

Larger Q factor more distance between cranks.
I think what they mean is lets just say your bottom bracket measures 150mm from inside to inside of your cranks and say a Q16 set of cranks will give you an additional 16mm per side for a total distance of 150+16+16 =182mm between inside faces. Q factor of zero is a perfectly straight crank arm.
My bike has boost dimensions. 110mm in the front and 148mm in the rear.
So my chain stays don't stick out a whole lot to interfere with the crank arms in the backend. Like I said I have almost an inch from the chain stay bar to the inside of my crankarms.
My buddy has a fatter rear end which is 197mm spacing and my crank arms on his bike hit his chain stay. So he needed a larger Q factor crank from what I can use.
The closer the better as long as everything spins free.

 

[TPEHAK]

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.

What is the proper specs for Bafang m620 crakarms?