[nowlan]

This isnt a DH specific question, but I was wrenchin in the garage and im scratching my head.
I have a BB mount Lopes guide on a Tracer, with Stylo cranks and a Chromag CR. I dont think the parts or the frame matter. Its an External BB.
Heres the issue, my top guide rubs a bit with the chain and I thought, hey if I can bring that chainring out a mm id be golden. So I put a 1mm BB spacer, between the BB and the BB mount boomerang which gave me the correct spacing. When I instal the cranks and torque it down the cranks wont turn at all. Without the spacer its fine.
Why is this?

 

[Racebike]

The Truvativs are very sensitive to spacing like that.

The reason is that the small stepped bit on the axle (non drive side) needs to contact the bearing on the non drive side.

If you space the drive side out so the stepped part doesn't make contact you will put a boatload of stress on the bearing and things will seize up.

Try solving it another way, can you move the chain ring and space the guide plate/roller out instead?

 

[nowlan]

What do you mean by stepped bit? The part that links into the removable crank arm?

 

[Schneidie]

What do you mean by stepped bit? The part that links into the removable crank arm?

The spindle on truvativ cranks has a step the is meant to seat against the non drive side bearing. If it does not, the bearing is preloaded by the crankarm and you have a bad day.

 

[MichaelT]

Nowlan,
From what you have described, I will forgo a lot of other preliminary questions and I would start with this trouble shooting process:
1) I would measure your BB shell width. If you do not have a set of calipers then check the website. I think it is a 73 mm, but don't quote me on it. Is the face of the shell clean and free of paint?

2) Check Truvativ's website and see if your BB / crankset combo is compatible with 73 mm shells and etype deraileurs / chain guide mounts. Some Truvativ cranks, including Stylo, ARE NOT compatible with 73 mm shells and bottom bracket mounted chain guides. Bottom Brackets | SRAM

3) If item #2 shows you that the set up you have is not compatible with a 73 mm shell, sandwich mount, then depending on the age of the BB and crankset, you might be able to get a bb assembly with a longer spindle. If item #2 shows you that it is compatible then let us know. We can go from there.

When in doubt, hit the reset button. Clean all parts, inspect for wear, double check chain ring hardware & chain ring mounting position, grease where appropriate, install, double check fitment. Also make sure all slider parts are installed correctly.

If the BB shell is measured to specification, the alternative is to directly contact the components regarding this matter.

Michael