migrantwing

No matter how I set up my front DR, there was chainrub when in small front/large rear and large front/small rear. NOTHING I did to tweak the FD position would prevent the rubbing. After trying everything, even widening the FD cage slightly, I still got chainrub. It could only be one other thing...a less than perfect chainring.
I know that the bike hasn't fallen over or been in any kind of accident that would bend the chainring, so it must have been bent whilst in transit at some point or other. I have succeeded in sorting this problem out with square taper BB's with this method (video below) but is it possible with a Hollowtech II BB? The setup on HTII has it so the little 'pin' on the large chainring sits directly behind the crankarm and the little arrow on the smaller chainring lines up with the crankarm too. Would the front shift be as smooth if I rotated the chainrings to a different position to try and alleviate the run-out in the chainring , or does it require that the pin and arrow are ALWAYS set up to be behind the crankarm? It is not that there are a few bent teeth on the chainring, it's more like the chainring is not perfectly flat when placed on a flat surface making it run out for the distance of about a third of the chainrings circumference, hence the rub. It's more warped than bent per se.


View: How To Fix Chainring Wobble - YouTube

JohnDThompson 

I'd just avoid those gear combinations.

migrantwing

I hear ya. Just seems to defeat the purpose, doesn't it. It's not as if I'm cross-chaining or anything. May have to get the rubber mallet out.

cny-bikeman

Rotating the chainrings is not a logical solution. The fact that you have wobble on both the large and small chainrings (presumably at the same spot of rotation) means that it is an arm of the spider that is the problem, not the rings. Rotating the cranks may not work, so tweaking the spider would be the solution. A rubber mallet may not be enough to move it, plastic-faced dead blow hammer (used carefully) might do it, but I always pushed and pulled rather than hammered to straighten spiders.

fietsbob

are the chainrings flat? ( remove and compare on a flat surface) the arm may be warped, some how.

it may be just less perfect than you wish it were..

New bike? see if the retail seller, shopcan work thru their distributors in a QC warranty claim ..
parts, Other than tires, typically have a year for that..

Homebrew01

Can't you micro-adjust ("trim") the front derailleur to prevent the chain rub ?

Dan Burkhart 

Have you approached the limit screws with a screwdriver? I saw no mention of that.

AnkleWork

How much runout (lateral and radial)?

migrantwing

Yes, it may in fact be the spider, CNY, or maybe an amalgamation of the chainring AND the spider. I'll take a better look tomorrow and take the bike outside. Thanks for the info.

migrantwing

3 year old bike, fietsbob. I have placed the chainrings on a flat surface and if I put my weight on one side of the chainring(s) it lifts slightly, maybe 2-3mm. It's not much, but enough to cause intermittent rub when using 34/28 and 50/11

migrantwing

Nope, homebrew. No amount of trimming will help. It's probably a factor of a slightly bent chainring or chainrings and a slightly bent spider arm. IF they're both out a few mm, it's gonna throw everything off. It's not a huge problem, but it's annoying.

migrantwing

Limit screw settings are fine, Dan.

P.S I enjoy your YouTube videos

Dan Burkhart 

Thank you very much. I have a lot of fun making them.

fietsbob

If you can't mechanically flatten them, or turn the job over to someone who can, you just need to buy new ones .

migrantwing

Sorry, Anklework, I missed your post. Radially they seem fine, the lateral run out id probably a good 2-3mm. This is what is causing the rubbing on the front DR as it's intermittent.

migrantwing

You are most welcome. I thought I was subscribed to your channel, but wasn't. I am now

migrantwing

My friend has a press. I'll see if he can work some magic on them.

fietsbob

IDK about the new 3D outer rings . flat ones can be done with an adjustable wrench .. the hard part is
measuring the run-out, to know when its right . again.

machine shops use dial indicators for that , precision measurement.

AnkleWork

That definitely needs fixed.

migrantwing

I'll see what my friend and I can do.

migrantwing

For sure. It makes adjusting the hi and lo limits and cable tension adjustments so that the chain doesn't rub impossible. There's no rub at all, then there's rub when the chainrings get to a certain point near the FD.

jgcycle

I was reading this post since I was getting chain rub on the front der when high at the front and smallest 2 cogs, its an Ironman 6 to 7 speed conversion with Sora brifters. After what seemed like tweaking every possible thing, der alignment, height, bent it out a little, had the cable tighter than heck, chainrings ok, re-bent a spider arm at the screw hole since it seemed .5mm high when sitting on glass, check BB, ...then FINALLY loosening the cable wire and re-doing it did the trick. Must have allowed the der to move farther outward. Ha-ha on me. Took 3 weeks to figure that out.

hueyhoolihan

old Henny Youngman joke:

while lifting his arm, the patient says to the doctor, "It hurts when i do this".

Doctor says, "Don't do that".