Electric Bikes Conversion Kits EMTBS eRoad/Commuting What's New?

Cranks and pedals

W

winterdog

Pedelecer
Feb 22, 2009
168
0
Hi Wisperites,
any one know if i can slap on any type of crank arms I can lay my hands on on to my 905 se , or if they have to be special ones.

i managed to have a good slip the other week on a patch of ice and bent my left crank arm a bit and took a good chunk out of my pedals. I was a bit embarrassed but still made it in time for the train after i got my breath back. I have slapped the crank arm it in a vice and tried to hammer it back a bit but it just dose not feel quite right. any thoughts /experiences ?

thanks
davidk
 
S

Straylight

Esteemed Pedelecer
Jan 31, 2009
650
2
Any square taper compatible arms will be fine, but beware of the really cheap ones. I made this mistake when swapping to a larger chain-ring, the replacement was not a good fit and it creaked/clicked from day one.

If you want to replace both sides then you'll need to get a new chain-ring to go with it, as the Wisper original right-hand crank is an all in one design without a removable ring. It takes a bit of research, first determining the chain-ring size i.e. the number of teeth you require, then what BCD (bolt circle diameter - also known as PCD) your favored ring is, and finding a crank to fit it (with right number of arms).

Personally, I went about this completely the wrong way round, by first buying a cheap crank-set, then a ring to fit it, only to find that the cranks were rubbish, then discovering that square taper cranks with a BCD of 110mm were as rare as hen's teeth. Finally found this one after much searching.

Oh, and the other thing to consider is the length of the arm - I just measured the old one as I was happy with it.

Alternatively, you could always ask Norman (Wisper service) if he'll sell you one :) .
 
Last edited:
1

1967geezer

Pedelecer
Oct 9, 2009
36
0
Maidenhead, UK
I think contacting Wisper spares would be the best solution (providing they keep them in stock).

Last year I had a similar problem, two tumbles in one day on black ice bent not only the crank arm, but the bottom bracket as well.

I did encounter two very minor problems, the threaded rings on the new bottom bracket would not allow the pedelec sensor to sit as it did before, I had to make a thin aluminium washer to pad it out.

But that should not be a problem for you, if you only need to replace the crank arm(s).

which leads to the second problem I encountered. The square on the new bottom bracket did not quite fit the square in the crank arm, with the result that the left crank came loose. Loose enough to come right off over bumpy ground, which meant the retaining nut was gone, lost in the long grass. Luckily I was able to make a replacement at work. But nothing I did would keep the crank on the square, it kept working loose every couple of days. In the end I had to take the bottom bracket spindle out and carefully file the square smooth. Once I had done that all was OK.

Which is all a very long-winded way of saying when you fit your new cranks, make sure they fit good and tight onto the bottom bracket spindle :)

Chris.
 
C

CeeGee

Esteemed Pedelecer
Feb 4, 2009
328
0
Weybridge, UK
When I used to ride a normal bike (many years ago), I always rode with slightly bent cranks. I found I got used to them after a few miles.
When, after months, or years, I replaced a bent crank and spent a few miles getting use to the straight one, it was a certainty I would drop the bike and bend the crank again.

Colin
 
M

Mussels

Esteemed Pedelecer
Jun 17, 2008
3,207
8
Crowborough
Straylight said:
Any square taper compatible arms will be fine, but beware of the really cheap ones. I made this mistake when swapping to a larger chain-ring, the replacement was not a good fit and it creaked/clicked from day one.

If you want to replace both sides then you'll need to get a new chain-ring to go with it, as the Wisper original right-hand crank is an all in one design without a removable ring. It takes a bit of research, first determining the chain-ring size i.e. the number of teeth you require, then what BCD (bolt circle diameter - also known as PCD) your favored ring is, and finding a crank to fit it (with right number of arms).

Personally, I went about this completely the wrong way round, by first buying a cheap crank-set, then a ring to fit it, only to find that the cranks were rubbish, then discovering that square taper cranks with a BCD of 110mm were as rare as hen's teeth. Finally found this one after much searching.

Oh, and the other thing to consider is the length of the arm - I just measured the old one as I was happy with it.

Alternatively, you could always ask Norman (Wisper service) if he'll sell you one :) .
Click to expand...
My '08 bike has a removable ring and is 110 BCD so in my case the crank you linked to would be all I'd need.
I think asking Norman is the way ahead, he can supply just the left hand crank which will be much easier and probably cheaper to fit.
 
S

Straylight

Esteemed Pedelecer
Jan 31, 2009
650
2
Hmmm, maybe they'd run out, or beeen in the middle of changing supplier when they built my bike - oh well...

BTW, the Sinz cranks are great, no creaks, no clicks, and as they're made for BMX, I'd guess pretty strong too. Oh, and the anodised finish is as good as new after several months' use, including being dropped a couple of times. The only thing I was concerned about was that the logos looked a bit ott in the photo, thankfully in real life they're not as flourescent, due to the matt finish.
 
Last edited:
W

winterdog

Pedelecer
Feb 22, 2009
168
0
thanks
i think a straight one for one from Norman would be mu best plan.
may be i should get a few spare as this bad weather has not let up here yet :)

davidk
 
You must log in or register to reply here.

Advertisers

Top Bottom