I've got a creak in my cranks!

[Caph]

I decided to try and tighten everything at the weekend to get rid of a minor creak coming from my bottom bracket when pedalling but I've managed to make it worse.

I tightened the Shimano style bottom bracket on both sides so that's definitely not the problem, but I noticed that my chainring crank had slight damage to the centre of each of the four sides of the hole that fits on to the bottom bracket. I then realised that my crank removal tool is slightly bigger than the hole! It's been slightly deforming the BB bolt hole every time I've been removing the crank (which I've only done a couple of times to be fair). So I'm pretty sure the creak is coming from the crank.

The other crank is normal size but the chainring crank has to be smaller to leave room for the magnet disc that slides on first for the pedal sensor.

I thought tonight I would try and remove the magnet disc and use a standard Shimano Acera chainring that I have so I used a piece of metal that is about the right size to fit between the BB and the crank removal tool bolt. Unfortunately it pushed the crank removal tool bolt too far back thus not giving it enough bite and I threaded it. It looks terminal.

So, does anyone know of a crank removal tool that will fit an electric bike crank that is the smaller size to cater for the magnet disc? Or does anyone have any tricks for using a standard crank removal tool with this size crank? I'm going to have to buy a new one in any case. It looks like I'll just have to put up with the creak for the time being and if it gets worse I might see if I can get a replacement crank from Powered Bicycles.

It dawned on me that if the magnet disc didn't slide on to the crank and instead clipped on to the chainring then standard chainring cranks could be used. Does anyone know of any magnet disc that attaches in this way?

Sorry for asking so many questions, but any answers will be greatly appreciated.

 

[torrent99]

I decided to try and tighten everything at the weekend to get rid of a minor creak coming from my bottom bracket when pedalling but I've managed to make it worse.

I tightened the Shimano style bottom bracket on both sides so that's definitely not the problem, but I noticed that my chainring crank had slight damage to the centre of each of the four sides of the hole that fits on to the bottom bracket. I then realised that my crank removal tool is slightly bigger than the hole! It's been slightly deforming the BB bolt hole every time I've been removing the crank (which I've only done a couple of times to be fair). So I'm pretty sure the creak is coming from the crank.

The other crank is normal size but the chainring crank has to be smaller to leave room for the magnet disc that slides on first for the pedal sensor.

I thought tonight I would try and remove the magnet disc and use a standard Shimano Acera chainring that I have so I used a piece of metal that is about the right size to fit between the BB and the crank removal tool bolt. Unfortunately it pushed the crank removal tool bolt too far back thus not giving it enough bite and I threaded it. It looks terminal.

So, does anyone know of a crank removal tool that will fit an electric bike crank that is the smaller size to cater for the magnet disc? Or does anyone have any tricks for using a standard crank removal tool with this size crank? I'm going to have to buy a new one in any case. It looks like I'll just have to put up with the creak for the time being and if it gets worse I might see if I can get a replacement crank from Powered Bicycles.

It dawned on me that if the magnet disc didn't slide on to the crank and instead clipped on to the chainring then standard chainring cranks could be used. Does anyone know of any magnet disc that attaches in this way?

Sorry for asking so many questions, but any answers will be greatly appreciated.

I'm a bit confused by this one.

As you've worked out the creak is 99% likely coming from your crank.

And, your crank is now duff (due to the deformation of the bolt hole), so you'll need to replace it one of these days.

However the magnet disc bit confuses me.
My impression was that the magnet disc usually goes on the bottom bracket spindle rather than the crank. So an ordinary crank removal tool should have no problems.
Do you have a different sort of magnet disc?

BTW Theoretically you could make your own magnet disc on a chain ring by gluing magnets *in the correct pattern, polarity and spacing* onto a chainring. You can get the tiny magnets from Maplins.

 

[Caph]

I'm a bit confused by this one.

As you've worked out the creak is 99% likely coming from your crank.

And, your crank is now duff (due to the deformation of the bolt hole), so you'll need to replace it one of these days.

However the magnet disc bit confuses me.
My impression was that the magnet disc usually goes on the bottom bracket spindle rather than the crank. So an ordinary crank removal tool should have no problems.
Do you have a different sort of magnet disc?

BTW Theoretically you could make your own magnet disc on a chain ring by gluing magnets *in the correct pattern, polarity and spacing* onto a chainring. You can get the tiny magnets from Maplins.

I didn't think I'd explained myself too well!

You're dead right that the magnet disc goes on the bottom bracket spindle, thus taking up valuable room that would otherwise be used by a standard sized crank, thus requiring a smaller sized hole in the crank to make sure it doesn't crush the disc. Which of course means that a standard sized crank extractor bolt is too large to use. That was the problem I was trying to describe anyway. I could easily remove the magnet disc if I could remove the crank first, but I've threaded my crank remover and I'm loathe to use another one and make matters worse, which was why I was asking if anyone knew of one that fitted an electric bike crank.

I like your idea about gluing on the magnets, which I already have of course, in the correct order and with the correct polarity. Also, if I remove the magnet disc and use a standard crank, it will sit much closer to the magnet sensor and probably work. Thanks for the idea. The creaking was worse than ever today!

I'm surprised that no-one else has encountered the problem of removing a crank with an undersized BB bolt hole. Surely everyone with a magnet disc must face the same problem?

 

[flecc]

I'm surprised that no-one else has encountered the problem of removing a crank with an undersized BB bolt hole. Surely everyone with a magnet disc must face the same problem?

I was also a bit puzzled as I haven't had a problem to date with this. Last times were with two eZee models, Quando and Torq 1 when I also replaced the fixed crank/chainwheel on the Quando with a conventional spider and chainring, not any special type. Both of these have a magnet ring at the rear of the spider/chainwheel, the pedalshaft possibly a bit longer than standard. It seems as though your's is different.
.

 

[Caph]

It seems as though your's is different.

That was the conclusion I was beginning to come to aswell. I'm going to have another go at removing the crank this weekend along with the magnet disc to see if a standard crank will fit OK. I'm starting to think the BB spindle may be a non-standard size on one side. I'll report back...

And thanks for the replies.

 

[Andrew harvey]

I assume here that we are talking about standard taper shafts as opposed to Shimano splined shaft.
Square tapered shafts are nominally the same size, but I have had the same problem, but it's not major.

It is the bottom bracket spindle that is longer or shorter, not the crank that is thinner. These spindles come in a variety of sizes from 63/108 to 63/128 mm, 63 is the size of the frame (63 mm), the 108/110/113/115 ....128 figure is the width of the spindle. This figure relates to the offset of the chain ring when bolted up tight, and allows for different rear frame sections and different numbers of chain rings.
It is not uncommon for crank extractors to jam into the square taper, particularly on squeaky cranks. With repeated tightening of the crank bolts burrs sometimes form, were the taper pushes on the aluminum which is also tapered. Experience seems to suggest that the act of tightening further compresses the aluminum on the out side of the crank causing the hole to close slightly, squashed between the steel bolt and the taper section.
The extractor itself might also squash with repeated use, (shorten and hence expand radially), that seems extremely unlikely, but they do come in hugely different qualities.
To stop a squeaky crank squeaking the normal solution is to remove it and check for burrs or raising that could restrict the fitment in some way.
A gentle fileing of any burrs or raised sections before reassembly normally works. If you can not see an obvious cause try turning the crank arms 90 degrees before refitting, so that they are fitted on different faces of the shaft. Its an old trick of the trade given me about 30 years ago, but don't tell everyone, it still surprises mechanics who don't expect you to succeed in curing a creak, they very rarely see what you've done even though they have just watched you do it.

If the magnet disc is the standard spoked type, you can just cut the spokes with pair of side cutters, throw the middle bit away and fix the disc back to the chainwheel with tie wraps.

 

[Caph]

Andrew, there are some great suggestions in there, many thanks. I'll try the filing and 90 degree trick at the weekend.

I'd never thought about standard tie wraps, so simple and yet so effective. I'll size up this option too.

The BB is a standard Shimano square tapered, not one of their new Octalinks (I've never even seen one!). Regarding the size of the hole on the cranks, one is definitely smaller than the other. I can push the crank extractor bolt through the non-chainset crank without any problem, but it won't quite fit through the chainset crank. I'd much prefer to get my bike working with a standard crank on a standard BB though, purely for ease of maintainibility.

 

[Mussels]

Regarding the size of the hole on the cranks, one is definitely smaller than the other. I can push the crank extractor bolt through the non-chainset crank without any problem, but it won't quite fit through the chainset crank.

I get the feeling you are the only person on this thread who has seen this, both my cranks take the standard size extractor and I think so do most others.
I couldn't see it before, what type of bike do you have?

 

[torrent99]

I get the feeling you are the only person on this thread who has seen this, both my cranks take the standard size extractor and I think so do most others.
I couldn't see it before, what type of bike do you have?

Yea definitely seems unusual.
On my 07 Wisper the cranks are normal square taper, requiring no special tools unless you count the crank extractor.
The bottom bracket however is much longer than normal and asymetirical. This is primarily due to the width of the rear wheel/motor combination which requires the BB to be wider to line up the gears correctly.

BTW I'm sure you know already, but do remember to grease the BB spindle when you fit the cranks to prevent them welding up.

That filing and rotating 90 degrees trick sounds brilliant!

 

[Mussels]

The bottom bracket however is much longer than normal and asymetirical. This is primarily due to the width of the rear wheel/motor combination which requires the BB to be wider to line up the gears correctly.

Deviating from topic slightly but that isn't so much the case anymore, the 09 models have the chainring much closer to the frame. It's close enough to stop the chain coming off every 100 miles or so anyway.

 

[rog_london]

Deviating from topic slightly but that isn't so much the case anymore, the 09 models have the chainring much closer to the frame. It's close enough to stop the chain coming off every 100 miles or so anyway.

I think that modification took place a bit earlier than that - rather like the high/low power control. Mine is a late 08 model and the bottom bracket is symmetrical and about 3.5" wide. The chain clears the battery by barely 3/8" when in bottom gear and it has never come off.

I don't know for sure, but I think the longer Wisper BB was a bit troublesome. I base that opinion purely on the number of posts in here relating to problems with it. Anyway, it seems now to be fixed. As with most things to do with engineering, it's best not to buy the Mk 1 of anything, though sometimes it's hard to avoid if you really have to have a new model as soon as it appears.

Rog.

 

[Caph]

Fixed! Well almost.

I've deduced that the reason for the smaller hole in the drive crank is twofold. One is that the magnet disc will only slide up to the end of the square tapered section of the bottom bracket axle so the crank has to stop short of this, secondly I've got a three ring chainset on my front crank and the smallest inner ring sticks out thus requiring the crank to stop even further out from the BB.

I figured that if I got a longer BB (the one that comes with the bike is about 114mm) then I could use my Shimano Acera drive crank whilst still keeping the crank about the same distance out from the BB, so I bought the longest one I could find, a 127mm Shimano BB. I collected it today and it fitted like a dream. The crank now fits snug in almost exactly the same place as the old one did and leaves about 5mm between the inner chainring and the BB, just enough for the 3mm magnet disc. Perfect, or so I thought.

That was when I deduced the second reason for having a smaller hole in the original crank - to prevent it sliding all the way up the square taper. So although I have enough room for the magnet disc, it is on the larger untapered round section of the axle which is too thick for the magnet disc.

I've come too far now to give up on a fitting a standard drive crank but I'm off on holiday this weekend so I'll worry about fitting the magnet disc when I come back.

Oh, and the creak? After fitting my Shimano cranks to the old BB it was much better (I had definitely caused some damage to the original crank) but still there. Oh well, I thought, it must be the BB itself. Then I fitted the new BB with the Shimano cranks and it was still there! So I started looking for any other explanation. I eventually found it. My bike has rear suspension and one of the hinges (well more of a bolt which tightens with an Allen key) is about an inch back from the BB. I checked it and it was loose. I tightened it and the creak is gone. I should have twigged really because I only got the creak going uphill and that's when the rear suspension is working hardest.

Mussels, I wasn't ignoring you, I missed your post. My bike is the Powered Bicycles Galileo.