bottom bracket wobbling effect

[fabieville]

After I installed the bottom bracket, the chainring and the crank arm, I turned the chainring by turning the crank arm. I found that the chainring was wobbling from side to side and this will cause the chains to come out of the chainring sometimes. But when I just turned the chainring by spinning the chainring only (crank arm not moving), the chainring was not wobbling. I guess this is because the spindle of the bottom bracket is warp (not straight). Am I correct? Or is this normal for all bottom bracket conversion with freewheel capability? How can I prevent this?

 

[Bike Xing]

On new freewheels I see a little bit (~1 mm) of side to side movement when the cranks spin. On very old beat up freewheels that have been in sand and mud I've see as much as 3 mm. It has never been enough to cause a chain to derail though. How much side to side motion are you seeing?

 

[boostjuice]

If the BB you have is an aysmmetric long spindle, square taper, 'First Components' branded unit as is sold by Cyclone/Sickbikeparts etc. then it is unsurprising you have a bent spindle. The spindles droop during the process of case hardening/heat treating them after machining, and it's luck of the draw as to how bad the one you get is, but Jim at Sickbikeparts confirmed all this.
It's poor form that they let these out the door with such bad tolerancing IMHO.

 

[eyukon]

Hi Fabian,
After fitting a new GNGE rev2 kit I also had a few (too many) mm of runout on the chainring, most obvious when spinning the crank backwards in the freewheel with the chainring stationary. I tried the crank in all four positions on the axle and found one where the runout is minimal. Did you find a solution?
David

 

[outofsquare]

Boostjuice is right on the money with his explanation, I was told by a toolmaker that parts that are heat treated need to have the effects of this treatment taken into account with heat treatment tolrences, I had exactly the same issue, he machined a shaft for me which he then had nitrite treated in liu of heat treatment and I have a great set up now.

Tom

 

[tmho]

I got the same problem with my GNG kit. Finally, I can only solve it by replacing the BB spindle.
For details, please see my post at http://endless-sphere.com/forums/viewtopic.php?f=28&t=54585.