Chain dropping between TA chainrings

[NHAero]

I'm using an 11s chain and cassette with a SunXCD crank that mimics the old TA Pro 5 Vis (Cyclotouriste) and using TA chainrings with the 50.4mm BCD. The TA Zephyr rings I've used on 110mm BCD cranks are marked 9/10 speed, and have not had this problem; the Pro 5 Vis are unmarked. After a lot of finicky work I have the CX70 fd working fine, but it occasionally drops the chain between the rings on a downshift (44T to 28T).
I've looked around the Web and there are differences of opinion about the cause, but I know the 11s chain width is narrower than previous chains. The inner ring is bolted to the outer ring, and they are separated by spacers (like fat washers) on the bolt body. My inclination, based on one person's solution, is to try to reduce the spacing using some stainless steel 1/4" flat washers instead of the TA spacer.

Comments? Other solutions?
Thanks, as always

[oldpotatoe]

Originally Posted by NHAero

I'm using an 11s chain and cassette with a SunXCD crank that mimics the old TA Pro 5 Vis (Cyclotouriste) and using TA chainrings with the 50.4mm BCD. The TA Zephyr rings I've used on 110mm BCD cranks are marked 9/10 speed, and have not had this problem; the Pro 5 Vis are unmarked. After a lot of finicky work I have the CX70 fd working fine, but it occasionally drops the chain between the rings on a downshift (44T to 28T).
I've looked around the Web and there are differences of opinion about the cause, but I know the 11s chain width is narrower than previous chains. The inner ring is bolted to the outer ring, and they are separated by spacers (like fat washers) on the bolt body. My inclination, based on one person's solution, is to try to reduce the spacing using some stainless steel 1/4" flat washers instead of the TA spacer.

Comments? Other solutions?
Thanks, as always

Look to where the front der cage touches the chain when shifting from big to small and gently bend that part inwards a wee bit. If you don’t want to do that adjust pitch of front der nose in or tail out just a smidge and when shifting from big to small, minimal pedal pressure and smaller cogs in back(helps chain angle)..

[NHAero]

Thanks, Peter, will try. Not much wriggle room on the in/out pitch I think, but the bending sounds possible.

Originally Posted by oldpotatoe

Look to where the front der cage touches the chain when shifting from big to small and gently bend that part inwards a wee bit. If you don’t want to do that adjust pitch of front der nose in or tail out just a smidge and when shifting from big to small, minimal pedal pressure and smaller cogs in back(helps chain angle)..

[bicycletricycle]

thinner spacers would be my first guess as well. If you want I can turn down those spacers on my lathe. Mcmastercarr also has a lot of spacers like that in the standoff section.

Originally Posted by NHAero

I'm using an 11s chain and cassette with a SunXCD crank that mimics the old TA Pro 5 Vis (Cyclotouriste) and using TA chainrings with the 50.4mm BCD. The TA Zephyr rings I've used on 110mm BCD cranks are marked 9/10 speed, and have not had this problem; the Pro 5 Vis are unmarked. After a lot of finicky work I have the CX70 fd working fine, but it occasionally drops the chain between the rings on a downshift (44T to 28T).
I've looked around the Web and there are differences of opinion about the cause, but I know the 11s chain width is narrower than previous chains. The inner ring is bolted to the outer ring, and they are separated by spacers (like fat washers) on the bolt body. My inclination, based on one person's solution, is to try to reduce the spacing using some stainless steel 1/4" flat washers instead of the TA spacer.

Comments? Other solutions?
Thanks, as always

[NHAero]

What might be the downside to thinner spacers?

And thank you for both the machining offer, and the tip on MMCarr

Originally Posted by bicycletricycle

thinner spacers would be my first guess as well. If you want I can turn down those spacers on my lathe. Mcmastercarr also has a lot of spacers like that in the standoff section.

[bicycletricycle]

more rubbing on the big ring when in the small / small combination. perhaps more chain drops onto the bottom bracket when down shifting but if the inner set screw is adjusted well than I doubt it.

Originally Posted by NHAero

What might be the downside to thinner spacers?

And thank you for both the machining offer, and the tip on MMCarr

[El Chaba]

Are the T.A. chainrings and spacers old? If so, the spacing was anticipated for 5 or 6 speed width chains and that is just a generation or two too far...at least for that size difference in rings, etc....So, I'll chime in with the others that a little off the spacers would be a good solution...That setup has to be the easiest to re-space as you are just narrowing spacers rather than the crank mounting interface as on most cranksets...

[NHAero]

The rings and spacers themselves aren't old, but it doesn't look to me that they differ from ones that ARE old, so yes, my first set of these cranks and rings was on a 2x5s set-up in 1972.
And yes, the experiment to change the spacers isn't hard to do.

Originally Posted by El Chaba

Are the T.A. chainrings and spacers old? If so, the spacing was anticipated for 5 or 6 speed width chains and that is just a generation or two too far...at least for that size difference in rings, etc....So, I'll chime in with the others that a little off the spacers would be a good solution...That setup has to be the easiest to re-space as you are just narrowing spacers rather than the crank mounting interface as on most cranksets...

[NHAero]

Because this setup gives me a low gear of 44/30 (2nd biggest cassette cog and big ring), so I only need half the cassette, at most, for the small ring.

Originally Posted by bicycletricycle

more rubbing on the big ring when in the small / small combination. perhaps more chain drops onto the bottom bracket when down shifting but if the inner set screw is adjusted well than I doubt it.

[NHAero]

I'm close to giving up on this. I had the idea that one way to narrow the gap was to flip the inner ring, because the teeth are asymmetrical and in the right orientation are biased inward. I did this and no chain drops between the rings. However, in the first half mile of riding the chain over-shifted past both the outer and inner rings. I can't restrict the fd travel more without the chain rubbing in some gears, even after I worked on reducing the runout of the TA rings. I think this is an artifact of the improper gap between the fd chain guide and the chainrings - it was 10mm and now it's zero - combined with the non-ramped and pinned TA outer ring.

I don't need this low gearing in my day to day riding on MV, it's a want for riding in places with real hills. I should have had Dave Anderson move the braze-on tab down when he had the frame back for painting last winter.

I'm reluctant to throw more $ at this, given the starting point of fd chain guide location. I think the 44-33 on the old Sugino AT 110mm BCD crankset, which I had set up at the 10mm gap, works because the rings have almost zero runout on a crank with a spider and the outer ring is ramped and pinned.

I'm open to suggestions. It's too bad, because the SunXCD crankset and TA rings is a reasonable cost solution and looks good on the bike. Likely the whole package is going back onto eBay....

[oldpotatoe]

Originally Posted by NHAero

I'm close to giving up on this. I had the idea that one way to narrow the gap was to flip the inner ring, because the teeth are asymmetrical and in the right orientation are biased inward. I did this and no chain drops between the rings. However, in the first half mile of riding the chain over-shifted past both the outer and inner rings. I can't restrict the fd travel more without the chain rubbing in some gears, even after I worked on reducing the runout of the TA rings. I think this is an artifact of the improper gap between the fd chain guide and the chainrings - it was 10mm and now it's zero - combined with the non-ramped and pinned TA outer ring.

I don't need this low gearing in my day to day riding on MV, it's a want for riding in places with real hills. I should have had Dave Anderson move the braze-on tab down when he had the frame back for painting last winter.

I'm reluctant to throw more $ at this, given the starting point of fd chain guide location. I think the 44-33 on the old Sugino AT 110mm BCD crankset, which I had set up at the 10mm gap, works because the rings have almost zero runout on a crank with a spider and the outer ring is ramped and pinned.

I'm open to suggestions. It's too bad, because the SunXCD crankset and TA rings is a reasonable cost solution and looks good on the bike. Likely the whole package is going back onto eBay....

Pinned and ramped outer ring that will 'grab' the chain w/o having the fder overshifting the chain to get it onto the ring.

[El Chaba]

The reduced spacing should help, but I'm thinking that there may be a couple other factors. These are small rings and they might be pushing the limits of compatibility with your front derailleur....and the height of the derailleur might be on the long side... The other factor is that the chain doesn't want to catch the small chainring because it is shifting with a pretty severe chain line on the smaller cog side of the cassette. I think it might be the combination of factors...This is the sort of thing that is pretty tough without looking at it right in front of you...

[zap]

edit

Originally Posted by El Chaba

These are small rings and they might be pushing the limits of compatibility with your front derailleur....and the height of the derailleur might be on the long side...

I wonder if shimming the front braze on derailleur (to move tail closer to the rings) would help.

I did this to my wife's custom Serotta with a step 76.5 st angle and that helped prevent over/under shifts.

[NHAero]

That's an interesting suggestion, thanks.
Right now the derailleur is right down on the rings, because I'm using the Wickwerx adapter. I could raise it again and try the shimming.
I'm using the CX70 fd because I thought that would be the one most adapted to smaller chainrings. I have a new R8000 fd in the box, but feel that is only a trial and error opportunity - there's nothing that clearly indicates that fd would be an improvement.
And yes, OP, a ramped and pinned ring would help - only SunXCD makes that, and I need both rings because of their proprietary BCD for the inner ring, so would like to have more confidence before i drop even more $ into this experiment :-(
Maybe shoulda bought the White Industries VBC system, but wanted to keep silver vs. black

Originally Posted by zap

edit



I wonder if shimming the front braze on derailleur (to move tail closer to the rings) would help.

I did this to my wife's custom Serotta with a step 76.5 st angle and that helped prevent over/under shifts.