Bicycle Mechanics - Chainring spacers in Ultegra cranksets?

Pulled apart my OEM FC-6500 crankset the other day. There are thin spacers between the spider and the inner chainring. I believe they were put there by Shimano, but these spacers don't show up on any exploded drawing.

I pulled apart another FC-6500 because the inner chainring had been assembled "backwards" - Shimano specs that the side with the lettering face the frame. There were no spacers in this assembly, but I also noticed that the cogs are offset slightly to one side of the ring. By flipping the chainring to the "backward" position, one moves the cogs toward the frame from the spider, just as the spacers do.

Anyone know anything about this?

Are the cogs directional?

Don't know the specifics of this crankset... but there are a lot of chainrings which have the teeth slightly off-center, as you describe, so that you can flip the ring over to tweak the chainline. I've used this a couple times in building fixies to adjust the chainline by 1 mm or so.

It sounds to me as if someone added the spacers because the chain was dragging on the side of the big ring when the inner ring was installed backwards causing the spacing to be too close. But it doesn't sound like something Shimano would do intentionally. You are correct about the tooth count spacings facing the frame on the inner ring.

Al

If those spacers are ~ 1mm, send them here :P

It sounds to me as if someone added the spacers because the chain was dragging on the side of the big ring when the inner ring was installed backwards causing the spacing to be too close.
You got that reversed. The one assembled correctly (and apparently by Shimano) is the one with the spacers. Besides, the way the cogs are offset, it looks as if flipping the inner ring increases teh spacing.
Both show chain scarring on the inside of the big ring, though. Is that abnormal?


But it doesn't sound like something Shimano would do intentionally. As I say, the bike was newly assembled from an OEM kit. The builder didn't care enough to get the crank arm lengths right, so I seriously doubt he took the trouble to rebuild the crankset.

If those spacers are ~ 1mm, send them here :P
No, they are quite thin, <0.5mm. I intend to change the crankset today and I'll mike them to see.

Btw, you know you can build up to 1mm with thinner spacers? ;)

No, they are quite thin, <0.5mm. I intend to change the crankset today and I'll mike them to see.

Btw, you know you can build up to 1mm with thinner spacers? ;)

Yes but uh, I prefer one stack of 1mm than 10 x .1mm's :)

[QUOTE=DMF]You got that reversed. The one assembled correctly (and apparently by Shimano) is the one with the spacers. Besides, the way the cogs are offset, it looks as if flipping the inner ring increases teh spacing.
Both show chain scarring on the inside of the big ring, though. Is that abnormal?

QUOTE]

You're right, I missread your post. I don't remember ever seeing spacer washers on Ultegra 9-speed cranks, my wife has had 2 9-speed Ultegras.
Don't know about scarring.

Al

Spacers are 0.2mm.

And they are between the spider and the outer ring, not the inner ring as I said first. (Not that it makes any difference, 'far as I can see.)

When I took apart my RX-100 crank, it had the spacers. I have an ultegra crank of a similar vintage that doesn't have them. I don't know if they are necessary, but they don't hurt.

I'm leaving mine in. I just wonder what in the assembly is sensitive to a 0.2mm difference in chain line?

I am using Stronglight chainrings and I get a slight audible rubbing when the chain is on the small chainring and on the 2nd and 3rd smallest cog. I bought the .5mm spacers and I'm going to use them to get a little wider chainring to chainring spacing but wait! Which way are the Stronglight chainrings supposed to go on? I always thought that the imprinted tooth count number should be on the outside (facing out) so that you could read it from the right side. But now someone is saying it should be on the outside for the large chainring and the inside for the small chainring. Is this right? I can't tell visually which way would give me the wider spacing. I guess I could install the rings and mike it and then install them another way and mike it again. Any opinions?

Outside out and inside in is true for Shimano. I can't attest to any other brand.

As to whether flipping the rings is a valid way to adjust chainline, I'm still waiting to hear something definitive. But if it works, fine. If not, you can always change it back.

One thing I've noticed, though, is that the Shimano intermediate ring has hooks to grab the chain during shifts. If those aren't on both sides (and I didn't check yet to see if they are), flipping the ring would screw with shifting. (Also waiting to hear whether the cog pattern is directional.)

I am using Stronglight chainrings and I get a slight audible rubbing when the chain is on the small chainring and on the 2nd and 3rd smallest cog.

If you mean the chain is rubbing on the side of the big ring the normal cure for this chainline problem is to move the entire cranset out with a 2mm bottom bracket spacer, goes between the bottom bracket cup and the bike frame. You sould be able to pick up one of these from your LBS.
I don't know which way Stronglight rings face.

Al

Flipping the rings can work to adjust chainline but it may degrade shifting performance on chainrings with ramps/pins and irregularly-shaped teeth. So when chainring performance will be just what it was before ramps/pins and irregularly-shaped teeth. Which is, plenty good unless you've got front indexing.
I've flipped some chainrings because they were worn out, so you basically get a brand-new chainring that way.

I took off the chainrings (Stronglight) and examined them. I do not have modern bikes so this is going to be a cure only for pre-brifter folks. I layed the chainrings on a flat shiny table one way and then flipped it over for the other view. The difference was less than 0.5 mm (a very small difference indeed). I determined to flip the inside chainring which by itself would give me a wider spacing between the big and small chainring which might have been all I needed to prevent chainring rubbing, at say a .75 mm wider distance total. I added to that distance five 0.6 mm spacers between the spider arm and the inside chain ring. This gave me a total of about 1.3 mm wider spacing. I then put the bike on the stand and victory! No more annoying rubbing. This is a good thing because I have almost crashed in the peloton at plus 25 mph because like a moron I was listening for the rubbing sound. BTW, putting a spacer under the fixed cup is not an option for (as others have suggested to fix the rubbing problem) because I am already using a Campy bottom bracket in place of a Superbe Pro Suntour one which I either couldn't afford or couldn't find. This substitution spaces me out about 2mm by itself which throws off Q factor.

Garth

I replaced the shimmed crankset with an unshimmed one of the same model (with longer arms). Nothing else changed. I threw the chain on a vigourous front upshift, so maybe the 0.2mm spacers do make a difference!

I'm leaving mine in. I just wonder what in the assembly is sensitive to a 0.2mm difference in chain line?

Those little spacers are added to the crank to accommodate a wider chain. They have little to do the chainline, however that is an end result of adding spacers.

I have a 9-speed Chorus crank with a 7-speed chain. The 0.4mm spacers add the necessary width to facilitate shifting from the big ring to the small ring.