Pedal crank alignment

Jonda500

Member
May 10, 2014
82
2
8
Canberra, Australia
I am currently making a motorized Northern Star ATB with a jackshaft shift kit.
It had a one piece crank which I am converting to a three piece unit.
What has me totally baffled is that the crank on the chain wheel side is half an inch further out than the other crank????
The crankshaft is offset like all that I've seen are. I have the longer side on the chain side - I think this is how they always go... I even pulled apart another bike to check!
The frame appears symmetrical where the crank goes through.
I am using a conversion kit from SBP's.
My other motorized one piece crank bike did not have this issue.
I use 125mm crankshafts to keep the stock width.
I tried reversing the crankshaft, but that puts the chainwheels too close to the frame.
What could I have done wrong?
 

Jonda500

Member
May 10, 2014
82
2
8
Canberra, Australia
This is my other bike with the crank conversion that I am trying to replicate.
Yes, I know the chains are swapped - I like to do this so the derailleur chain is easy peasy to remove, the stock crank width can be retained and some other reasons too.
20171231_155439.jpg

I use 11 loose ball bearings of the correct size (per side) - I wish I didn't now as I am gonna have to pull the crank back out to figure this out!
 
Last edited:

Jonda500

Member
May 10, 2014
82
2
8
Canberra, Australia
Well I just measured the difference and it's actually closer to a quarter of an inch, and the inner chain wheel is very close indeed to the conversion kit part on that side... so I really should just ignore it!
I would really love to know why this happened though... hmmmmmmm!
 

Jonda500

Member
May 10, 2014
82
2
8
Canberra, Australia
Okay - it's fixed!
So I pulled out several more crankshafts from my spare bike collection and found one that's the same on the short side, but several mm's shorter on the long side- strangely it was installed with the short side on the chain side??
I pulled apart the cranks and installed this ~122mm crankshaft. The balls all stayed in the cups so that was good and easy, unfortunately the removal threads in the left SBP's crank mysteriously went bad so I had to use a spanner to screw the removal tool in and now my tool has slightly damaged threads - bummer! :( -In the future a ball joint separator will be used to remove this crank!
The clearance between the inner chainwheel and that side conversion kit part is now around zero - depending on the crank angle it either just clears or lightly rubs. I am not concerned as both parts are coated black so I think once the paint rubs off it wont touch any more..
I am just happy both cranks clear the frame by 25mm now! Symmetry restored! :)