Bikebeast

I recently brought my bike in for repair. The problem is that the main pedal crank won't stay put due to stripped threads. The bike mechanic advised the unmentionable, a new crank hub, but there are no parts available for this Chinese made bike. Meanwhile, he is investigating ways to secure the crank. Any suggestions? (Welding, rethreading)? This is an ebike that I purchased over a year ago for $700. I am still awaiting the worst scenario from the bike shop.

operator

So you stripped your crankarm pedal threads? How badly is it stripped? You can probably chase it if it's not too bad or helicoil it.

Is the crank steel?

old and new

Probably not steel .. as heli-coil as operator stated. JB weld would work, depending
Myself ... I can't imagine going for a crank if .... I've taken radical, more extraordinary measures on auto engines so ....

davidad

You need to go to Sheldon Brown's site and learn the proper terminology for the parts so that we might be able to help.

old and new

WE think he needs a pedal, that site is apt to confuse him.


TO THE OP, Do you meen the pedal itself ? as davidad pointed out, you seem to be confusing the terms.

Bikebeast

Sorry for the confusement...what I'm attempting to describe is the big sprocket (containing the chain, right side arm/pedal). That whole sprocket got loose and began to wobble while I was pedaling the bike. I went to the bike shop and the bike mechanic discovered that the nut holding the sprocket in place was missing. He installed another nut and found out that the threads were stripped. He's not even sure if he can fix it and will give me a call/estimate early this coming week. He suggested contacting the manufacturer and obtaining a new part(?) to replace the worn out threads, but parts/support for this ebike is not available in the USA (Kysmo made in China). I appreciate everyone's input and will keep you posted.

old and new

Thankyou for the re-reply .. Good Luck !

JohnDThompson 

Pictures would be very helpful. Perhaps you have a cottered crank and have lost/damaged the cotter pin? This is not a part often found in modern boutique shops.

Bikebeast

OIC TMB, you're referring to the cotter pin on my VDub....lost a wheel once without it!

w98seeng

Do you mean this part?
bottom_bracket.jpg

I would figure it is easy enough for your LBS to get a replacement spindle.

You might even be able to put in a cartridge bottom bracket.

Bikebeast

The enclosed attachment depicts the large chain sprocket that came off. The female threading on the hub is worn out so that the sprocket bolt won't tighten up. Hate to get stuck in TimBukTu in this situation! Fortunately I was able to throttle a block back home with the loose sprocket hanging by a thread.....literally speaking.

SJX426 

A picture IS worth a thousand words.
No suggestions. If your LBS can't replace the BB and crank with a common unit, there isn't much recourse. Good Luck!

thenightrider

Without having an up close picture of the thread it's hard to determine how much you have to work with.

If your stuck between a rock and a hard place and can't find a replacement aftermarket spindle or a sealed bottom bracket that will fit you could try a few "handy man" attempts. To do all of these you'll need to have the spindle removed

If you have enough thread on it to hold the nut on but not enough to have it lock you could try drilling a hole through the spindle as close to the nut as possible. After this use some red locktite to hold the nut on the thread as best as possible and place a cotter pin through the hole. If your not too handy any local machine shop could do this for you as you'll need a drill press and and a good clamp/press. If you do try it yourself remember to take your time with the bit and use plenty of oil so you don't change the temper of the metal.

The next two solutions involve re-threading.

The first solution is take it to a local welder and have them build up the end near the thread again and then re-tap afterwards. This should work pretty well and provide most of the original strength of the spindle back.

The next solution which is not as desirable is to re-thread the entire spindle at a smaller size.

Hope this helps...

Bikebeast

thenightrider, thanks for your input....all very excellent ideas. i was able to find a slightly larger bolt and tighten it snugly over the worn threads. it's tight and snug, and i rode my bike several miles without incident. i feel that the issue has been resolved, at least for now, anyways.

thenightrider

Glad to hear you found a solution....

Though have to admit that I'm a tad bit confused. Did you mean that you used a larger nut which would make no sense. Or, your bottom bracket uses a bolt to hold the crank set on? Unfortunately your picture makes it a bit hard to tell as well as your postings LOL

If it is the latter and you used a larger bolt to do your fix then what you've essentially done is re-tapped the spindle using the new bolt. If you used a large enough bolt you'll have hopefully created a fresh new thread which will be a permanent fix. Meanwhile if it was only slightly bigger it will have just expanded the existing thread slightly and will hold. But, the expanded thread will be weak and may cause an issue again in the future.

If your crank set comes loose again due to a stripped thread the proper fix will be to ream it out with a drill bit which is slightly bigger then the diameter of the thread of the current bolt used. This can be done with a cordless drill/electric drill without even having to take it off the bike if you are careful.

After that tap it with a course metric tap which should help prevent the thread from getting stripped again in the future barring any defect with the steel used to make the spindle.

In the meantime use some blue loctite on it. It's weaker then the red loctite and can be loosened using hand tools but is strong enough to prevent the bolt from coming loose again due to vibration.

Anywho... Enjoy riding your bike again

Homebrew01

That picture is only worth 200 words.

Bikebeast

"If it is the latter and you used a larger bolt to do your fix then what you've essentially done is re-tapped the spindle using the new bolt. If you used a large enough bolt you'll have hopefully created a fresh new thread which will be a permanent fix."

thenightrider,

That is exactly what I did, retapped the spindle using a new larger bolt. It appears to be a permanent fix. Thanks for the additional info . This is quite a learning experience!

Bikebeast

"That picture is only worth 200 words"

And a penny's worth of input....

sivat

Considering that 95% of the bikes sold in the US are made in china, i would be surprised if you couldn't find a bottom bracket that will fit. It may have to be a beach cruiser or bmx part, but i bet you can find one.

wrk101

+1 Almost all bikes are now made in China. So finding parts for a chinese bike should not be difficult at all. Probably would be harder to find parts for a bike NOT made in China.

And most bikes use common universally sized parts. So I can't see the parts being anything unique. I would find anothe bike shop, or start reading up on the Park Tool site or similar and do the work yourself. It really is not tough!

rs1101

what i dont understand is how one would even fit another bolt into the spindle?how hard was it to install? crank spindles are usually a very hard metal and if that one stripped , id ask myself if i trust riding that bike? Ive never seen a stripped spindle that wasnt the result of some horrendous abuse.

efetch

i'm guessing it has bsa threads. if so you can tap out to Italian threads which are just slightly larger. you should have enough metal thickness on that bike to do this without any problem. really Italian are created by reaming out the old threads, only the threads are removed and then you cut new threads into smoothed inner shell

Bikebeast

Thanks everybody! This has been an informative thread and continues to be so..... As stated earlier, I secured the crank with a slightly larger size bolt, thus retapping the spindle (see thenightrider entry). I did not use any loctite, and as of 40 miles later, am still pedaling to far away places. The new bolt was first hand threaded, then 97% torqued until firmly seated. It can possibly be unscrewed/rescrewed (if absolutely necessary) using the new threads. I do not know how the threads were initially damaged unless someone beforehand carelessly crossthreaded it or it was damaged in transit. Will keep you posted at the 100 mile mark!

Bikebeast

Hit the 100 mile mark today on a self repaired crank set. I also removed the rear (cable) disk brake assembly and adjusted the inner pad. The bike now stops on a dime without the squelching wake-up call. Overall I am pleased with this bike and it's reliability when traveling afar.