Chainline Question (not enough?)
 

I'm working on this Peugeot mixte. I have fitted a very nice Sugino road triple (74/110 BCD) with 30-40-50 chain rings. I don't know the spindle length in the bottom bracket, but I've converted it from the factory cottered spindle. The bottom bracket cups tighten down nicely on this spindle and preload is set appropriately. I like how closely the crankset snugs up to the frame, but I think my chainline (distance from rings to seat tube) is too small, and I'd like clarification/guidance before I change any parts. I have visited Sheldon Brown's website on chainline, and I definitely have less chainline than he notes there. I am measuring about 35mm in the small ring (picture 1 below) and about 40mm in the middle ring (picture 2 below). Sheldon Brown sez I should have 45 from the middle ring, with a road triple.

My issue is the very old (and cheap) Sun-Bow derailer will not move the chain to the small ring. It will bind on itself before moving far enough left (picture 3 below). This seems consistent to me with a chainline measurement that's too small. It appears that I will have to replace at least one of my current pieces of equipment (derailer, crankset, spindle).

My question: is any nicer or more modern derailer going to move far enough left to work on a ring with a 35mm chainline, or am I going to have to switch to a longer spindle to move the crankset out a little bit? I want to be able to use the small and middle ring on this crankset, and swap the large ring for a chain guard (either find one or make one myself out of another chain ring), and I like the 30-40 small-middle size for this bike so priority #1 , if I can, is keeping the current crankset. If I can just swap the derailer for a more modern one, that would be my desired move, but I'm hoping to hear from those more experienced to know if that's just a dead-end road due to my current chainline.

Thanks in advance for ideas and comments.

https://farm5.staticflickr.com/4819/...f28041a6_b.jpgpug_cl_1 by jnjadcock, on Flickr

https://farm5.staticflickr.com/4831/...d9efbe75_b.jpgpug_cl_2 by jnjadcock, on Flickr

https://farm8.staticflickr.com/7822/...6c6d1be5_b.jpgpug_cl_3 by jnjadcock, on Flickr

How is your alignment fore to aft with the chain on the middle front ring and the middle of the cassette?

I think it's dead-on. The middle ring on the front and the middle sprocket on the cassette (7-speed) results in a perfectly straight chain.

Context: this bike originally came with a 5-speed freewheel and hub spaced to 120mm if I recall correctly, and I currently have a 7-speed cassette/hub spaced to 130mm in the frame.

You probably don't want to buy another bottom bracket, since it's a French threaded one you will need and they can be hard to find. You can move the right crank outward 2-3 mm with bottom bracket spacers (aka freewheel spacers) behind the the drive side cup flange. The non-drive side cup will recede into the bracket shell a bit, but that's no biggie. Check that this won't bring the non-drive side in so far that the left crank comes uncomfortably close to hitting the chainstay. You need a bit of clearance for safety and for the crank to settle a bit onto the axle over repeated tightening. Maybe this will bring your front derailleur into range. Don't worry about your cranks being off-centre a bit, as long as there is chainstay clearance. Also don't fret about chainline as long as you are within a few mm and the whole thing works reliably and smoothly.

Spa Cycles in the UK has a variety of chain guards for those 110/74 Sugino cranks, and an amazing collection of chainrings of all qualities too. Making a triple into a low double is a standard trick "over there", and the chain guard will really look like it belongs on that Peugeot. I say go for it. BTW, that bike deserves metal fenders and nice tidy little rear rack.

I'll bet that a cheap used Suntour ARX front derailleur will do that shift without issue. Go to a bike coop or look on-line. I haven't, but I cannot imagine it will cost you more than $10-15.

Ben

Maybe it's the angle of the pic, but it looks like the FDER is mounted way too high?
How much clearance above the large ring when in that position? Should be about 2-3mm.

I do not believe I have ever seen cables pass on top of the bottom bracket. No answer, it's just odd. :foo:

Thanks -- that's a good idea. I'll need to check that the NDS cup won't thread so far into the shell that I can't get the lock ring on (I think it would be close). I will have plenty of crank arm clearance on the NDS. Else, I could just get one of the "insert" bottom brackets designed to install a sealed cartridge bottom bracket into a French shell, and fit one with a slightly longer axle. I don't read wonderful things about them in terms of quality or durability, but this also isn't a bike on which I'm putting thousands of miles a year.

Thanks for the link; I'll check them out. I was planning on finding a used ring with a pattern that I liked and just grinding the teeth off and smoothing/polishing that surface. That would certainly be more labor-intensive than just buying one, and probably not worth it if they're available for a fair price.

Thanks; I'll check it out. I do have a spare FD or two around here that I could try to mock up. The trouble is, none of them have the integrated cable stop that this bike needs. Else, I could fit one of those clamp-on cable guides with the curved tracks that would allow me to ditch both of the short cable sections.

Yes, it's just the angle of the photograph. The derailer is over the small ring in that picture. When moved over to near the large ring (that I won't be using anyway), it just barely clears the teeth. Treating this as a small double, it probably is too high relative to the middle ring, but I can't go too much lower with it, or the bottom of the cage will conflict with the rear shift cable.

Yes, it's somewhat common with older bicycles, though I do think they typically used clamp-on or brazed-on cable guide "tracks" under which the bare inner cable would slide. This is the first one I've seen that uses short sections of cable housing over the bottom bracket shell. It seems to work well, but it does require a front derailer with an integrated cable stop, which is not necessarily very common, at least with modern derailers.

Just remember that if you move the crankset in either direction it will affect the fore to aft alignment. It obviously doesn't have to be perfect, I just wanted to make sure you were considering all the variables. Cool classic color on the bike by the way!

Yes, my 1985 Bridgestone 400 routed the rear derailleur cable above the bottom bracket just like that and it also came with a short section of housing covering the inside the braze-on guide.

The only downside to that routing became apparent when I switched the OEM 52T big chainring for a 46T. When I lowered the front derailleur to have the correct clearance the tail of the derailleur just cleared the cable. A smaller "big" chainring wouldn't have worked.

Right -- which is why I want to leave it where it is if at all possible (reference crankset position and chainline). At this point, I think I'm going to try fit a few different front derailers and, if one of them works, I'll just need to put one of the clamp-on cable guides on it and run it without those short cable sections. This Sun-Bow derailer has a narrow cage with completely straight sides to it. I imagine a more modern cage, with the various shift-enabling contours to the cage, would help push the chain far enough inboard to make that shift to the small ring.

Because there's at least one response that said a different derailer would probably work with the current chainline, I'll give it a shot. One of my local bike shops has a pretty good selection of used parts in boxes in The Back, so I may hit them up at lunch today and see if I get lucky.

https://www.spacycles.co.uk/m2b0s210...nguard-110-BCD

Wow -- about 11 USD for a very handsome chain guard! Thanks for the lead. Once I get this thing sorted and set, I'll contact them to see if they'll ship to a yankee.

how old are you?
 

It was how it was done in the 70's and earlier.. Built a frame like that , myself,, in 75

Housing stop is on top of the back end of the chainstay, then..






...

I definitely cannot re-space the bottom bracket cups with a cassette sprocket spacer inside of the DS cup, because it would pull the NDS cup too far in for the lock ring. So I want to keep that stuff as-is.

Fortunately, it looks like I'll be able to. I think I have lucked up with some parts. I scored a pair of 105 derailers that look nice on this bike. The yellow "105" on the RD matches my yellow outer cable housing. It's an FD-5504 and an RD-5500. The FD looks to be designed for a triple, as it has a fairly large cage with lots of shifting contours in it. My chain sits in the lower sections of the cage on the small ring, where the cage is pretty narrow, and it looks like I'll have to trim it with every couple of RD shifts. The middle ring puts the chain up in the wider section of the cage. I know these are the types of compromises that I have to take when working with older equipment that doesn't really go together, and I'm okay with that. I don't have a cable guide yet, but shifting it by hand demonstrates to me that this will work just fine. It pulls the chain off the middle ring with a quickness.

The RD is nice, but the B-pivot spring seems rather weak. I had a 12-28 cassette on the hub and I couldn't adjust the B-pivot tight enough to keep the upper cage wheel out of the large sprocket. It was fine on the next smallest (a 24T), so I just rebuilt the cassette using that as the largest sprocket. It's now a 12-13-15-17-19-21-24, and all of the sprockets are from the same S/T family except for the 24, which is an E/G from an HG50 mountain group. The close spacing seems to shift GREAT, and the derailer stays out of the sprockets.

I bought an inexpensive Campy dual downtube cable guide on eBay today, so that should be in the mail soon. It seems that Campag and Shimano are the only ones to make a dual cable guide, and the Shimano ones were usually pretty pricey. I paid $20 delivered for a parts box of 5 cable guides (including the dual Campy that I wanted) plus about a dozen smaller chainstay-sized clamp-on cable guides. Once I get that, I should be able to complete this drivetrain project and have the bike ready for spring. I appreciate this discussion on chainline!

https://farm5.staticflickr.com/4914/...027f11ea_b.jpg
pug_cl_4 by jnjadcock, on Flickr

https://farm5.staticflickr.com/4833/...480d267d_b.jpg
pug_cl_5 by jnjadcock, on Flickr

https://farm5.staticflickr.com/4905/...62fa1e96_b.jpg
pug_cl_6 by jnjadcock, on Flickr

Does the spindle have an offset? Many (most?) do.
Maybe you can flip it to get a few extra mm to the DS?

Yes it does, and it is already such, where the "long end" is on the DS.