jim319

I've been gradually upgrading my 1987 Trek 560 to Dura Ace 7400, and it's going really well. However, I'm trying to perfect the shifting and I'm having some chain line issues. I have a 600-series bottom bracket (original) and a 1050 series 105 front derailleur. I've upgraded to a FC-7400 Dura Ace front crank.

I adjusted the derailleur to be as parallel as possible to the chain line, but as I adjust the upper limit screw it doesn't quite have enough clearance to stop rubbing the chain before it starts to rub on the crank arm. I can think of three possible solutions, and I was wondering if any of you all might have some insight:


1) Less torque on the crankset. When I installed this, it seemed to push really far onto the BB spindle as I torqued it to spec. That does seem to have affected the chain line. I could disassemble and try to go easier on the torque setting (I used a torque wrench).


2) Dura Ace bottom bracket. This appears to have a 600 series BB. Any thoughts about whether a 7400-series Dura Ace BB would fit more snugly, pushing the crank further out?


3) Dura Ace front derailleur. I could get the FD-7400 front derailleur in hopes it would fit better.


Any thoughts? Thanks for the insight! It's a great bike--I happened upon it at a thrift store years ago and have loved it. I tried to include pics but I'm a new user so I don't think I can.

Piff 

Just to make sure, what position was your rear derailleur in when you adjusted the front derailleur to be parallel to the chain line. Smallest rear cog? Largest? Middle?

plonz 

I’m going to guess the 600 BB uses a different spindle length and if so, #2 is the solution I’d try.

jim319

The rear derailleur was in the smallest cog, front was on the large chainring.

Plonz--I've been reading Shimano's excellent tech docs and it appears in the 68mm shell (which I have), the Dura Ace spindle is shorter by 1mm (112mm for DA, 113mm for 600), but I'm with you--the fit may be different and I think the DA BB is much more likely to have the correct chain line even though the spindle is shorter.

jim319

By the way, it's awesome that Shimano has all the manuals posted, even for these 1987 products.

plonz 

I doubt the 0.5mm difference will change anything. Is the chain hitting the cage at the front, rear or entire length? I’m thinking maybe your derailleur shouldn’t be parallel to the chain in the gear combo you were using.

rccardr 

I’m confused. Just checked the chainline on a half dozen bikes, including several,with 740X, amd cannot for the life of me figure out how the FD could hit the inside of the crank arm.
Yes, the cage should be parallel to the big ring.
It should only have to move far enough away from the seat tube to clear the small cog in big/small.
What’s the size of the spindle? ‘600’ doesn’t tell us enough.

jim319

I have a bunch of pictures, but I can't upload them until I hit 10 posts--I'm sorry. I believe it's the standard spindle length for a BB-6400 on a 68mm shell--113mm. It's the bottom bracket that came with the bike.

jim319

It's hitting the cage at the front towards the top, so I may try rotating the derailleur to make it a little less parallel. The problem is that when the chain is on the big chainring (front) and smallest cog (back) the chainline is SLIGHTLY angled outward. That prevents me from rotating the cage too far inward, and increases the risk that it doesn't clear the crankarm.

Piff 

I think we really need pics. Based on a little reading, I also think that the 7400 crank has a slightly different taper profile (JIS low profile), but there are anecdotes of people using both JIS and ISO spindles with it.

Prowler 

Just to be sure that your "aperture " is open enough, do not over focus on just the BB. VERY odd that the crank arm hits the FD cage. Check that the FD is OK. I've seen some "field modified" FDs - either modified by owners or rocks or logs or limbs kicked up. Straight cage, twisted, etc?

Also study the DS crank/rings - straight, installed correctly, etc. Did some ancient wizard put a few spacers between the big ring and the arm for some wizard only reason? Anything bent? Compare to other DS cranks. IIRC Sheldon Brown promoted a chain line measurement of 43.5mm from center of DT to midpoint between the rings. Check that. It's worked well for me but I've also seen considerable variations that work OK too.

Looking forward to the photos, especially looking down from the TT.

mechanicmatt

When you finally get a chance to take a pic, the best views will from the crank side and a view directly above the derailleur looking down. It sounds like the derailleur may me mounted too low or the cage not parallel to the chainring line.

Retoocs

You don't align the derailleur to follow the chain line. Align the flat portion of the cage to be parallel with the chainring. Set the gap of the cage to clear the chainring teeth by 1-2mm.

SJX426 

jim319 check your chain line. Which sprocket does the the chain have to be on for a straight shot at the chain ring. If you don't understand chain line, google it. It is critical for effective shifting and FD adjustment.

dddd

Dura-Ace tapers are closely compatible with other JIS tapers, but this does not sound like a chainline problem at all.

Is the outer plate of the front derailer straight/flat?

Is a very wide chain perhaps being used here?

Chainring good and straight/true???

Seems like a crankarm bent inward would be obvious with the pedal rocking.

jim319

Please excuse a few extra posts as I try to get to 10 so I can get pics up here. Outer plate looks straight, as does the chainring.

jim319

Looks like about the third sprocket (from the smallest) for a straight shot at the chainring.

jim319

I'll take a look at the cage. Also, I'll get a picture uploaded as soon as I hit 10 posts.

jim319

Just FYI, the bike originally had a 105 biopace crankset.

jim319

Let's try for pics after Post 10.

SJX426 

One like this would help but with the chain on the large ring
P1020194, on Flickr

jim319

jim319

There we go! Pics worked this time. I tried to get the right angles.

rccardr 

This is not a bottom bracket or chainline issue. Your small ring clears the chain stay and that’s the most important functional consideration.

My best guess is either the arm is bent or the chainring is wrong-or at least incorrectly mounted. On the 7400 crankset sitting in front of me, there is 7.5 mm of clearance between the face of the big ring and the inside of the crank arm. The chain peg hidden behind the crank arm is maybe 2mm from resting on the inside of the crank arm. At full extension, there is 4-5mm of clearance between the outer cage and the inside of the crank arm.

Your arm/big ring assembly appears to have MUCH less clearance than that.

Is the outer ring a DA SG series part, or at least a Shimano ring? What is the size? While that series of FD is the ‘slanted travel’ design (the cage travels both forward and outward when shifting to the big ring) instead of the DA ‘straight travel’ design, it should still work. Just not enough clearance, Clarence.

jim319

Outer ring is a SG B53 Chainring, and there is 7.27mm of clearance between the crank arm and the face of the big ring. I'm pretty positive the crank arm is straight.

The pictures showing the lack of clearance between the chain/FD are with the chain on the smallest rear sprocket. Based on what you mention, rccardr, I'm wondering if the front derailleur might be the problem after all.

Ok--just realized what might be the problem. I'm running a 6-speed chain. I just measured the links and they are 7.76mm. I dug out my backup Sedisport chain and it's measuring between 7.02-7.1mm. This bike was originally 6 speed 105. Should I swap chains?