My KH Spirit cranks shows unstreightness, the disc is moving left/right of about 2mm in one revolution.
I am using KH Spirit Cranks since they show up on the market many years ago and I have just spot some unstreightness to my new pair (I used 4 different pairs already). After investigating the problem, I found out that my older pair has simmilar problem but hopefully to only half extent.
How the story begun.
I bought new KH Spirit Cranks 117-136 as spares in May 2017. They were waiting in my store for use. Month ago I mounted them to 20inch uni and used for 3 sessions of hockey. Yesterday, the time come to put them on Schlumpf hub with brand new 180mm disc. I was very surprised seeing that disc does not seem to be straight. It was strange for the new disc not being straight (flat). I took the disc and checked it on the table, it looked OK. When eyes cannot see I had to proceed with some accurate measurements, so today I did.
I see the following problems that might cause that the disc is not rotating straight:
- Disc is bent
- Disc mount, flange, or in this case KH Spirit Cranks is not straight.
- Hub axle is bent.
I did several measurements to find out what part is causing the problem.
One set of measurements consit with distances between disc and frame at different angles of wheel rotation. The graphs of measured distances in function of angle are sinusoidal. I was changing relative positions between crank, disc and hub among sets.
Ad.1 “Bent disc”
I compared 2 sets of measurements, the second one with the disc rotated 180 degree in relation to crank. There is a good correlation between graphs which means that the disc must be straight.
Ad.3 “Bent hub axle”
I compared 2 sets of measurements, the second one with crank rotated 180 degree in relation to hub. There is a good correlation which means that the hub must be straight.
After all above the conlusion is that disc mount on KH Spirit Cranks is not straight (the axle of disc mount is not in line with ISIS axle).
In my particular case the distances between frame and disc varies of about 2mm in one full rotation.
I have never before thought that cranks could cause such a problem. In the past I had always disc going a bit to left / right and always blamed the disc straightness.
Does any of you had simmilar issues?