My Crank Fell Off!

Chuy

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I come to find out after-the-fact this is a common issue on BBSHD motors, maybe also the 03 units - the crank arm bolts can loosen and if you don't catch it on time, like it happened to me, the crank can come off.

About a month ago my cranks started squeaking a lot. The bolts were a bit loose and I retorqued them to 25 ft-lbs. I didn't give them much thought - I thought parts were still settling down as my build had less than 100 miles.

Last weekend I went on my first off road ride, a 12-mile steep-hills, rutted, rocky, old fire road (Sheephead Mountain Rd). With two miles to go on the return ride, my left crank fell off and I could not find the crank arm bolt. Once at home I installed a new bolt with gobs of blue thread locker. If it loosens again, I will switch to red thread locker. I’m glad I saved a handful of crank arm bolts from previous crank replacements - I now carry an extra crank arm bolt in my rack bag.

Anyone else finding loose crank arm bolts? I assume this is more prone to off road riders.
 
Yikes! Thanks for letting us know, one more thing we never think about that should definitely be thrown in the ditty bag.
 
Don't forget an allen wrench. No doubt I will check the bolts when I ride now.
Screenshot_20240518-193045_Chrome.jpg
Every time I order from aliexpress I throw another set of these in my basket. They fit in any 1/4 inch bit holder, go up to 12mm and take up almost no room. Of course, if I keep reordering them, they will eventually take up room but they are great to have in each little gear bag.
 
@Annieolnie That seems overkill for a bike kit. You would need the impact driver. Unless you have a compatible hand driver. I carry a multi tool kit that includes a chain breaker. I’ve had it almost ten years and has served me well. I recently added a cordless air pump. I had it on my motorcycle, but it is now on the eBike.

Multi Bicycle Tool (19-Function, Silver) https://a.co/d/7R8KB33

Nulksen Tire Inflator Portable Air Compressor for Car Tires-150PSI Cordless Air Pump Bike Tire Pump with Pressure Gauge for Car Bike Motor Ball,Orange https://a.co/d/8BIEC26
 
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@Annieolnie That seems overkill for a bike kit. You would need the impact driver. Unless you have a compatible hand driver. I carry a multi tool kit that includes a chain breaker. I’ve had it almost ten years and has served me well. I recently added a cordless air pump. I had it on my motorcycle, but it is now on the eBike.

Multi Bicycle Tool (19-Function, Silver) https://a.co/d/7R8KB33

Nulksen Tire Inflator Portable Air Compressor for Car Tires-150PSI Cordless Air Pump Bike Tire Pump with Pressure Gauge for Car Bike Motor Ball,Orange https://a.co/d/8BIEC26
Actually, these fit in a small screwdriver style bit holder. They also fit any 1/4 inch driver or multi-tool that can handle standard bits. They have saved my bacon more then once because these were in the pouch on the bike and my multi-tool was in my pocket. Perhaps the picture makes them look bigger then they are. They are the width of a standard hex bit just longer, so they can get around spokes or wiring and can be used at a right angle if you need more torque. They are around 1/3 the weight of any bike tool I have owned, which always seem to have gargantuan hinges at the ends, anyway, I like them.
 
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I haven't had that problem on our e-bikes but I have better quality aftermarket cranks on all of our e-bikes and keep them torqued pretty tight. The stock bafang cranks aren't the best and square taper cranks have always had problems especially with hard use and heavier riders. I used to ride mountain unicycles and before ISIS splined cranks existed, square taper cranks were definitely the weak link that and snapping spindles.

If your crank doesn't stay tight with blue lock tight you don't want to use red lock tight it really means you need a new crank arm. Once a crank comes loose and if you rode it until it fell off it may have wallowed out the tapered square hole in the crank and it will just keep coming loose. If you did damage it that is. I don't know if you have any experience with red lock tight or not but it requires I think 500 degrees to break its bond and I wouldn't want to use a torch on my motor spindle and you would get your crank arm way hot. You really don't want to use red lock tight on anything that you wouldn't heat with a torch or that you intend to ever take apart again.
 
What I'm using are mountain bike or bmx cranks with a removable spider on the right drive side. I have a couple of pairs of Kookas and a pair of Rock werks, these are both cnc cranks the Kookas are my favorite because they have very little Q factor (offset) The are getting really pricy on ebay and hard to find. here's a drive side for $125 https://www.ebay.com/itm/276452882223?itmmeta=01HY7CMZZDYG9Q8XNYVSE11FHF&hash=item405de0372f:g:xo4AAOSwNG9mN6rZ&itmprp=enc:AQAJAAAA8JLOWpiBbh10nACU06tcgnjv9mKxdH6XyGzXc/XZuU1SgfVB5iNDwu42biYuANc6tKBSbarNEEjE2mUJRF5orKTra2iH9T+OYDXGfePncCD2Aw3iUNl0tXqDzLmxXhbE4Y3MbBzhY2wiXFAoa0VKrIWP0FNT2IOg0KBe/83EZudsVfT7FBTa5AdTDv2oeH1WxbtD4qOV/SqatpVxoUHi2hLPHyTVXnPLrwEpf/nlvWRztHItgNG6vqrWoNs3ZJtS6T4sHsaX+fWXfC3ayhqIkjOo+qoza7OFlgO15jxa+U6PThd48jMksebmfs4y8IR7kA==|tkp:Bk9SR-j_0-zxYw

I didn't pay much more than that for either set new. I think around $150 a set but I've had them for probably twenty five years.
 
Links to eBay may include affiliate code. If you click on an eBay link and make a purchase, this forum may earn a small commission.
I haven't had that problem on our e-bikes but I have better quality aftermarket cranks on all of our e-bikes and keep them torqued pretty tight. The stock bafang cranks aren't the best and square taper cranks have always had problems especially with hard use and heavier riders. I used to ride mountain unicycles and before ISIS splined cranks existed, square taper cranks were definitely the weak link that and snapping spindles.

If your crank doesn't stay tight with blue lock tight you don't want to use red lock tight it really means you need a new crank arm. Once a crank comes loose and if you rode it until it fell off it may have wallowed out the tapered square hole in the crank and it will just keep coming loose. If you did damage it that is. I don't know if you have any experience with red lock tight or not but it requires I think 500 degrees to break its bond and I wouldn't want to use a torch on my motor spindle and you would get your crank arm way hot. You really don't want to use red lock tight on anything that you wouldn't heat with a torch or that you intend to ever take apart again.
Yes, as a DIY auto mechanic, I’ve used the red stuff many a time. Heat and solvent can be used, but if you control how much red stuff you use, you can use regular hand tools to break the bond.
 
Actually, these fit in a small screwdriver style bit holder. They also fit any 1/4 inch driver or multi-tool that can handle standard bits…
That’s what I meant by the hand driver. I have several in my bike tool box. But for on the bike, I like the compact multi tools, otherwise, I will lose them.
 
I had one of my crank bolts get loose a few weeks ago, I also tightened it up and it happened again.
I used a few drops of the blue locktite and it's staying in place. When the weather starts to cooperate I will take the bikes off the rack for a maintenance and also add the blue to the other crank bolts.
 
For big fat bolts the that with a lot of thread area you might actually want purple instead of blue. Blue can set big bolts pretty firmly.
I know purple is really for smaller bolts but when I just need a little security the purple can be handy.
 
@Chuy. Same thing happened on my BBSHD. On mine, the rt side worked itself loose with relatively few miles on it. It was probably within 150 miles. I caught it before the crank fell off. I could feel something was off. It didn't make any noises. I thought it was a problem with something inside the motor slipping at first. The crank arms are part of my regular tightning check routine now. I suppose I may have not tightened it enough when I placed the motor on, but I haven't been having the same problem on my other regular bikes. Not sure if it is the BBSHD or mechanic error. I am using Lekkie Buzz Bars.

The people from Lekkie had me send them some pictures of the inside of the crank arm where it connects to the spindle of the motor. They were checking to make sure the corners weren't rounded out from the bolt working itself loose. They told me if the corners were rounded, I would always have an issue with the bolt working itself out, and I should check it regularly.
 
@major masingil I torqued mine to 25 ft-lbs twice - when I first put the bike together in January, and two weeks before the crank fell off. The bolts turned quite a bit the second time around but I dismissed it as the parts settling in. My corners are not rounded. Either the spindles or crank arms are poorly made. Other than a Schwinn tandem with one-piece cranks, all the bikes I ever owned have had square spindles and none have ever loosened. And I’ve never had to apply thread-locker before.

This same mtn bike I’ve been riding about 17 years and put thousands of miles off-roading through three bottom brackets and three cranksets before the eBike conversion and I never had this loosening crank arm issue before. I too will have to get used to checking the crank arm bolts periodically.
 
welp.....super glue and baking soda...just sayin.

can be released with heat..
 
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