May have damaged thread on new Bafang BBS02 motor. Any easy solution?

[Encantador]

As a complete novice, I thought I had done well fitting this kit. Unfortunately, not quite worked out how I expected.

Obviously all my fault, first problem was right pedal falling off, new crank arm, sorted.

Now the left crank arm has come loose where it attaches to the motor. When I got it back and remove the bolt there were metal filings on it, I am no expert but assume that means damage to the thread which is obviously part of the motor and not as easily rectified as a new crank arm.

I changed the bolt to the old one which I had taken off the bike when I did the conversion, added blue loctite and tightened it up. Today after about a mile and a half I tested it and it needed half a turn to tighten it fully again.

I will try it again before doing anything about it, but what options do I have if it keeps coming loose?

Thanks

 

[Fordulike]

I would highly recommend buying a torque wrench and hex socket set. I had problems with loose crank arms when I was tightening by guesswork. Now I use a torque wrench to tighten to 40 N-m and have never had a problem since.

 

[Encantador]

Thanks for the reply.

Are they best purchased separately, most 'sets' on Amazon only go to 20-25Nm?

 

[Fordulike]

Thanks for the reply.

Are they best purchased separately, most 'sets' on Amazon only go to 20-25Nm?

https://www.screwfix.com/p/magnusson-torque-wrench-1-2-x-18/6879v

https://www.screwfix.com/p/magnusson-1-2-drive-hex-bit-socket-rail-6-pieces/5207v

Might seem a little expensive, but worth every penny in my opinion. You can use the torque wrench on your bike, as well as a car.

 

[Encantador]

Thanks again, I will try that first.

being a pessimist, what other options are there if this does not work?

 

[peter.c]

The thread is damaged, a re-tap of the thread is a solution [but not for the faint hearted] if it cleans the damaged thread and holds with loctite all ok .But if not its deep fun fixed a tsdz2 with a a hole drilled in the pedal arm then tapped a thread and used grub screw down onto one of the flats on the shaft , the motor shafts costs mega£ and is wait from china

 

[Fordulike]

If the thread is damaged, as Peter says, a replacement axle shaft is an option. You can buy just the axle, but as you mentioned you are a novice, a complete axle/gear assembly may be the way to go. Replacing just the axle can be a PITA.

You can buy from Green Bike Kit, but may find UK vendors selling the assembly.

Here's the link for the one from Green Bike Kit:

https://www.greenbikekit.com/bafang-8fun-bbs-kits-and-spare-parts/8fun-bbs01-bbs0b-maintenance-repair-related-parts/bafang-8fun-mid-crank-motor-clutch-for-replacement.html

 

[Encantador]

Thanks again for the replies, plenty to think about. I have been reading about Helicoil, is that something worth considering?

Maybe I can find somewhere local with the tools and know how to do some sort of re-tapping if required. I am guessing if re-tapping is something you can do, what you are working on doesn't make much difference.

What sort of business might I find locally?

 

[peter.c]

The shaft will not have enough wall to helicoil the local engineering shop will have the taps /dies set
or an old school car mechanic , the sets are cheap enough to buy on ebay, i will check but sure i used 8mm finish tap

 

[Encantador]

Am I right in thinking that if it is the inside thread that is damaged and therefore the problem re-tapping would mean making the hole/thread bigger (needing a new bolt if there is one) and fitting a helicoil/time sert would keep it the same size so the existing bolt will still fit???

 

[peter.c]

The tap cleans the damaged thread i used a finishing tap and luck had it the hole was drilled deeper than the original thread so could take a longer bolt once re threaded
A helicoil needs a lot of material around the original hole as it is machined out to take a larger plug , in which has the original thread is in the centre most common use car /motorcycle engine block or spark plug repairs
But as it is a steel shaft will not work the total dia is to small

 

[xmakelucia]

Contact your supplier, always they can provide custom parts.

 

[KeithMac]

Helicoils are quite thin, I'd be surprised if you couldn't have one fitted?, local car garage or motorcycle shop maybe.

We use Wurth inserts which are a better repair but an M8 insert uses a 9.5mm hole iirc.

 

[KeithMac]

Other option is an imperial thread and allen bolt if one is marginal bigger.

 

[Encantador]

so far having been tightened properly it appears to be holding, but only done about 20 miles.

Thanks for the replies.