MB33 

I have an SR Apex triple with a 28 tooth granny. I built the bike last year, it shifted fine for the first 100 miles or so but as the chain and rings got dirty it would occasionally not shift all the way to the granny but sit on top of the rings. This year, after a thorough cleaning, it still does it occasionally. Only moderate wear on the rings and chain. How should I file the granny to prevent this from happening? Would filing the inside edge of the middle ring help force it over to the granny? Any advice would be appreciated.

genejockey 

The chain appears to be engaging the teeth on the bottom of the ring but not the top. Any chance you need a new chain, rather than to take the drastic step of removing metal you can't put back? Have you checked the chain for elongation?

steelbikeguy

I've had a similar issue on my Sugino AT crank set up as a half-step-plus-granny, although it happens between the 46T and 49T large rings. If I'm not making a quick shift between the rings, the chain can sit between the two rings. If I'm not paying attention, the chain can sometimes jam between the rings and get stuck.

The basic problem in my case is that I'm running a 8 speed chain, which is narrower than what the Sugino AT was designed for. I suspect that the problem would go away if I used a wider chain. I guess I haven't tested this hypothesis because I've adapted my shifting method to quickly/firmly/decisively shift and avoid the problematic mid-zone.

You might have some luck with making fast shifts to the granny ring, and maybe even adjusting the derailleur's low limit screw to allow the derailleur cage to move a bit further inboard.
Or... put a wider chain on? You haven't mentioned the type/width of chain that you are using.

Steve in Peoria

for reference, here's a token photo of my Sugino AT and bike:

70sSanO

I would never file aluminum teeth. My guess is the FD is not set up properly. From the top view, it doesn’t look right.

Not sure of the number of cogs you are running, but if you are shifting when in the smallest cog, the angle may not allow it to drop into the inner ring.

John

Edit Added: I can’t honestly say whether it is the angle or where the chain is hitting the FD outer plate. I suspect the 28t might play a part in this.

smd4

I would definitely stay away from the file.

MB33 

Previous posters have stated they've had good luck with filing teeth on these SR rings for better front shifting. I'm pretty sure dddd was one of them.

I am using an 8 speed chain. It has about 150 miles on it, I don't think chain wear is an issue. The slightly narrower chain width might be adding to the issue, but I don't think it's the main cause. I don't want to go to a vintage 5 speed chain because I want the ability to use quick links on this bike.

I'm pretty sure the derailleur is aligned properly but will doublecheck when I get home. I'll also try adjusting the lower limit a little more in to see if that helps.

Trakhak

The photo taken from above the chainrings shows that the gap betwen the leading edges of the derailleur inner and outer plates is too great. (I've seen bikes where the bike owner has deliberately bent the front of the inner or outer plate because he doesn't want to have to trim the front derailleur position while shifting around in back. Bad idea.)

I suggest using a ViceGrip to squeeze those plates so that they're somewhat closer together. Use photos of new derailleurs as a reference to get the gap right. Take your time - there's an art to shaping the front of the derailleur cage for optimal shifting performance.

Also, small inner chainrings are cheap, and that one appears to be quite worn, judging from the size of the trough between adjacent teeth. Might as well buy a new one.

smd4

I just said *I* would stay away from the file.

If your shifting suffers to the point where you need to take a file to your chainrings, then to me your problem has just gotten way out of hand, and you're looking for shortcut solutions. It's very easy to remove metal; far too difficult to put it back.

MB33 

I loosened the lower limit a bit and that appears to have mostly eliminated the problem. The chain was already rubbing on the outside of the cage in small/small before so I had it loose enough. Now it rubs on small/2nd cog a bit but I'm fine with that. It appears the only time the problem happens now is when shifting from big ring/small cog to small ring/small cog, which I'll have to train myself never to do. Thanks all.

79pmooney

Needing to trim the FD outboard a little to eliminate chainrub in the small-small is just about a given. I doubt I've ever had a triple that didn't and I've been riding them 50 years. Small to 2nd smallest usually ribs. I consider it a given that after shifting, I have to pull the cage back a little depending on where on the freewheel/cassette I am.

It looks to me like the inner ring is too far inboard for the width chain you are using. Hanging up like your photo is a nuisance but if it jams between chainrings, you've got a bigger problem. (I'd look at the outer and middle rings too.) The solutions - a narrower crankset for the chain you are using or make deflectors to kick the chain inboard to the next cog. I don't know any site that will give you good ideas on how to do that. I drilled holes in the chainring spiders, inserted SS bolts and ground them to a ramp-like shape. Very much a Mark 1 prototype. Works but not ready for publishing.

repechage

Shift with Authority.
make sure the mechanism is clean and well lubricated.
might even reduce the cable tension a tiny bit.
with most front mechanisms ,it is the spring doing the work.

finally, the cage can be finessed a bit to encourage downshifting. Look at the region of the cage where the chain passes when in the smallest ring- manipulate that toward the center line of the bike.

seypat

The FD doesn't look in line with any of the chainrings, particularly the back of the cage plates towards the rear cluster. It's not going onto the 3rd ring because the rear of the plate cages is not aligned along the chainline. The rear of the outer plate is too far away to do it's job.

mech986 

I would suggest the following:

1) Get to a local bike shop and have them measure the chain for elongation or stretching as mentioned above. Thinking (or guessing) is not the same as knowing unless the chain was NOS or new within the last 100-200 miles. If the chain is stretched, the small cog may not engage well anymore.

A chain like the SRAM PC-870 or the KMC Z8.1 (formerly the Z51), all master link compatible would be a very inexpensive solution. These two have been mentioned as quite compatible with 5 and 6 speed ultra freewheels.

2. Similar question for the inner cog. Closer inspection suggests some of the granny cog’s teeth appear nearing a shark fin like shape which to me suggests heavy wear to the point of needing replacement. In itself, could be the cause of the problem. If budget is really tight, some might suggest flipping the ring around assuming the chainring bolts still clear. Otherwise, a new alloy (or steel if you really need longevity) compatible BCD and chainring bolt chainring would offer as new performance from the ring and chain perspective.

3. I agree with the above posters about checking FD cage width, cage depth (some early 70’s FD cages are not really meant for deep small rings/chains like later purpose built triple FD. Same with adjusting height and angle of the cage to give best case clearance in your most commonly used ring/cog combinations.

4. If possible, re-examine your chain lines with each front ring. This will tell you how much lateral movement your FD and chain would have to tolerate should you go to extremes. Chain length and rear derailleur cage height and chain take up may need to be optimized.

For example, on my Campagnolo Nuovo Record triple with a custom 74BCD 28T small ring, it wasn’t shifting correctly into small/big 34T without without the top pulley contacting the big cog. This was because the drivetrain had been set for Big/big combo using all 116 links of a new KMC Z8.1. Consequently there was too much slack and not enough rear cog clearance. Realizing a big/big 53/34 combo really wasn’t efficient (middle 42/28 is almost the same), we took out a link and now it shifts great for the climbing gears I’m most likely to use. I also tend to live in the top 3 cogs most of the time so I worry less about the chain line in the big 53/18 or 53/14 and optimize the inner rings’ chain lines if possible.

bamboobike4

No clue. My granny was pretty shifty, as was her husband.

MB33 

LOL!!!
Thanks all, a nudge inward on the lower limit has been the solution. Yeah it was a bit out of alignment also (but some of you might be confusing the dt cable guide with the fd cage). Now all is well in Pro Tour land. I might even do an amateur tour on it soon.

ThermionicScott 

Glad to see the issue get resolved before the files came out.

The smallest ring of a double or triple usually doesn't need or get very much tooth-shaping. The chain either gets dropped down onto it, or pulled away from above. It's the bigger rings that had more room for improvement.

verktyg 

MB33 et al:

When installing or adjusting the front derailleur, the gap between the arc of the derailleur cage and the outer chainring should be about 1mm to 3 mm, maybe a little larger on a triple.

Looking down from the top, the cage should be parallel to the large chainring. It cage is misaligned in the right picture.



verktyg

oneclick 

Some cages do not have parallel plates. What I look at is my estimate of the midline of the shape - set the front mech there and run through the gears, adjusting the angle slightly if my guess is wrong.

rumrunn6

used a small grindstone on a power drill to remove a cpl small "tags" or "burrs" on an old worn/damaged chain ring, to try to reduce chain suck. eventually cleaning the chain helped reduce/eliminate the chain suck. but recently had a shop replace the whole drive train which the tech said would completely eliminate the chain suck, & it has. regardless I found it very difficult to work on the chain ring while it was attached to the bike, w/ the drill & grindstone. also I was disappointed at how not smooth my work was. I got the tags off but ultimately that wasn't the best answer to my problem

https://www.bikeforums.net/bicycle-m...ring-burr.html

the burr

bamboobike4

I thought the lettering looked like a Centurion. I saw a fully kitted ProTour of that color at the Hilly Hundred in Indiana. Beautiful.

JohnDThompson 

It may just be a camera artifact, but it appears that the front derailleur could be tweaked (rotated slightly clockwise) to be more parallel with the centerline of the frame. I'd look into that before attacking the chainrings.

JohnDThompson 

In those cases, I've found setting the outer cage plate parallel with the frame centerline to help shifting performance.

branko_76 

Yes, that looks strange

branko_76 

......something is not right

MB33 

It's like that in the picture because I spun it a few revolutions while riding to try to get it on the granny, then took the picture. When it initially happens it's above the teeth all the way around the ring.