Not MH related, need help with re-tapping, helicoiling my ebike motor. (1 Viewer)

[Encantador]

I appreciate this is not MH related but I know there is a lot of talented people on here, so hopefully someone will understand the above heading more than I do.

Having fitted a Bafang BBS02 kit to my bike the left crank arm became loose. When I removed the bolt there were metal filings on it which I suspect means the thread may have been damaged. The thread is part of the motor. It has been suggested that I should have used a torque wrench and tightened it to 40Nm. If I can confirm that is correct, that will be my next step, with some blue Loctite.

Planning ahead with my pessimistic head-on and with few skills in this area I am planning ahead should the above not work......

Although I would rather not, removing the motor is possible. It has been suggested that re-tapping and/or helicoiling may be an option.
I know that both of these options are not in my skill-set, just wondering what sort of small businesses would find either of these options a simple task. I am assuming that if you know how to do these and have the tools, what you are working on doesn't really matter, but I could be wrong.

Any suggestions of the types of businesses I should contact or any other suggestions/ideas would be most welcome.

Thanks

Steve

 

[Taran_Las]

A small engineering shop would be able to perform the work. (If they are interested that is.) Would a retap and a larger diameter bolt be a possible solution? That is dependent on the larger diameter bolt being able to pass through the current access and sit at the correct level.

 

[Jamesh]

Larger bolt with an Allen key head if a larger hex head won't fit any more.

Cheers James

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[Encantador]

Thanks for the reply.

I think they are pretty much a standard size, so dont think a larger bolt would pass through the end of the crank arm. The arm fits over the taper, the bolt just holds it in place, as I understand it at least.

 

[Clivefog]

Mobile mechanic should be able to helicoil it quickly and cheaply.

 

[Googlebot]

I don’t mean this to sound patronising but have you tried a bike shop?

I say this as it’s the last place I would look for a helicoil, a mate cross threaded his pedal last week and it failed mid ride. He popped in a local bike shop who sorted it there and then with a tap and helicoil. £26.

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[Jamesh]

Yes agreed but you could drill out the crank larger.

Another option would be to epoxy the crank and bolt in place so long as your not chris Hoy it should be ok. Is it drive side or non drive side.

If drive side the torque will be considerably higher and probably fail.

Cheers James

 

[Landy Andy]

A “timesert” is better than a helicoil if you get a choice. I’m not too sure how happy an engineering shop will be with working on the entire bike, would be nice if you could at least remove the motor, if not the crank.

I would start by checking the length of the bolt you have, and measuring the max possible depth/bolt length you could us. You may well find that a 20mm longer bolt will have plenty of decent thread to grip on, especially if you are planning on using thread lock. I’d also run a tap through the hole before putting any bolt, but especially one that has thread lock on, into the hole.

 

[Just smiffy]

An helicoil is where a hole has been enlarged to accept a larger thread but a helicoil (looks like a little spring) is threaded into it so the existing size bolt fits back in the hole…. Simples… Any good bike shop…

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[daveandsan]

Encantador is the crank tapered? If it is like most bikes you should get away with torquing it up but I would suggest you do this with a new bolt, not the old one.
The actual cranks are usually toughened so I suspect it may be the bolt that is suspect.
When I fit new cranks I usually torque them up and then after a week or so of use I re-torque them back up as being tapered they tend to bed in.

ps. As suggested a good bike shop will sort you out if you don’t feel confident.

 

[busbuddy]

A “timesert” is better than a helicoil if you get a choice. I’m not too sure how happy an engineering shop will be with working on the entire bike, would be nice if you could at least remove the motor, if not the crank.

I would start by checking the length of the bolt you have, and measuring the max possible depth/bolt length you could us. You may well find that a 20mm longer bolt will have plenty of decent thread to grip on, especially if you are planning on using thread lock. I’d also run a tap through the hole before putting any bolt, but especially one that has thread lock on, into the hole.

Like he said
Timesert every time....helicoil is stone age tech

 

[Itsmcb]

Yes the crank is tapered. You could try tapping the crank arm firmly back onto the shaft with a nylon hammer rather than relying on the bolt to pull the arm onto the shaft. Maybe lay the bike on its side with the other pedal bolt on a block of wood so as to not damage the motor when tapping. If the bolt thread is stripped that's a different matter. It should be obvious if the crank arm is starting to come loose as it will creak as you pedal.

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[Itsmcb]

I should have said you should also need a crank removal tool to draw the crank arm off the spindle, if not the arm definitely wasn't on tight enough.

 

[Encantador]

Thanks for the replies.

I replaced the bolt with the original bolt that I took off when I did the conversion. Not sure what the motor is made of and whether the filings I saw are more likely from the bolt of inside the motor.

been doing some research on the ideas mentioned. I think crank bolts are a standard size, am I right in thinking that if it is the inside thread that is damaged and therefore the problem re=tapping would mean making it the hole/thread bigger and fitting a helicoil/time sert would keep it the same size so the existing bolt will still fit???

Sounds like a visit to a couple of car mechanics and bike shops may be where I need to start (assuming the torque doesn't work.

 

[glenn2926]

Mobile mechanic should be able to helicoil it quickly and cheaply.

I was just going to suggest that.

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[Encantador]

I should have said you should also need a crank removal tool to draw the crank arm off the spindle, if not the arm definitely wasn't on tight enough.

I have done about 50 miles since installation, seems strange that it should stay on that long and then become loose.

 

[Ridgeway]

Plan A) establish if the either of the threads have been damaged at all, maybe even get a replacement bolt as a just in case.

Plan B) if the motor axles thread has been damaged (not the bolt) then you might be able to salvage it by passing a tap through it

Fingers crossed.

 

[daveandsan]

I have done about 50 miles since installation, seems strange that it should stay on that long and then become loose.

If they are not torqued up correctly they will work loose, that’s why I re-torque mine after a bit of use.

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[Ridgeway]

I have done about 50 miles since installation, seems strange that it should stay on that long and then become loose.

How much did you tighten it the first time ? (40mn is standard on cranks but it's a lot and unless you used an extension on that 7mm allen key then i'd doubt you tightened it that much by hand)

 

[Encantador]

I tightened it by hand and the stupidly rode it back when it came loose stopping every 300 yards or so to finger tighten it, guessing this is when any damage was done.

As per Plan A, having it torqued correctly might be enough (hopefully). I will get the bike shop to do that first and will chat with them about other options should that not work.

 

[Toady]

You are worrying me now as I will be fitting my Bafang motor on bike tomorrow. I will ensure I torque up cranks properly.

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[Itsmcb]

As above it's important to check the crank tightness occasionally. I also found with mine that I have to tighten up the big nut holding the motor to the frame a couple of times as the toothed washer which holds it to the cycle frame was bedding into the aluminium cycle frame. Again the slight 'creaking' sound as you pedal along is a clue that something isn't right any longer.

 

[Encantador]

You are worrying me now as I will be fitting my Bafang motor on bike tomorrow. I will ensure I torque up cranks properly.

Nothing to worry about, kit works fine, all of my troubles are self-inflicted.

Which kit have you gone for and where from as a matter of interest, may be doing the wifes next.

 

[Toady]

Nothing to worry about, kit works fine, all of my troubles are self-inflicted.

Which kit have you gone for and where from as a matter of interest, may be doing the wifes next.

I have bought the 250w kit with a 36v 20amp battery fitted on the pannier. Ordered by Amazon and it arrived 2 days later. Strange!

I have also purchased a new ebike chain and Lekkie bling ring (research) so now hoping I have everything.

I am in the same position. If it all works well then the wife will order the same. If not we will pick up an electric bike for the boss on our travels through Europe.

Luckily, my mate is a great bike mechanic so I am leaving the bottom bracket and cranks for him.

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[Toady]

Picture of the bike conversion.

 

[Encantador]

Looking good, have you tried it yet?

 

[Encantador]

Changed my mind about bike shop and purchased a torque wrench which arrived today. Hopefully get it done when the rain stops and see if that does the trick.

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[Toady]

Looking good, have you tried it yet?

Took it out for a spin yesterday and all went well. Running a 42 teeth Lekkie Ring on the front but may neeed to change the rear cassette as not suitable for hills