front mech - not reaching outer chainring

[hoogerbooger]

Background - should it be relevant
I'm transferring over parts from a 1983 Revell mixte road bike (that had a bent frame) to a late 70's Bob Jackson mixte frame. The Revell had a seemingly original Stronglite triple chainset. It was running with a 7 speed freewheel ( so rear stays must have been spread as was presumably 6 speed originally). I've spread the stays on the Bob Jackson that was presumably 5 speed originally.

The problem
The chainset inner ring bolts sit proud & just cleared the right stay on the Revell, but unfortunately just snags on the Bob Jackson. So I've added a 2 mm spacer on the chainset side, but the front mech now max's out and won't reach the outer chainring. (It's not the as adjuster screw preventing movement, it's max'd out)

I did have a look to see if I could find a granny chainring with recesses for the bolts - without luck so far.

The mech looks like an old shimano triple...but according to Sheldon Brown most doubles would have the same reach ?

So do mech's differ in reach ? I only need about 3 mm more reach and wondering if that might solve it.

( a more drastic solution might be to bash a recess into the stay and remove the spacer....but obviously I don't want to go there if avoidable)

If Mech's differ in reach any suggestions on ones that would have more range ?

Suggestions for a solution most welcome

[foxyrider]

The bash of the chainstay, if done properly, is the easy answer - many steel frames have been treated this way without issue. Find your local frame builder, he/she should be able to do the job sympathetically.

[NetworkMan]

You could try an FD intended for a 34.9mm downtube and use an eccentric shim. I presume your downtube is 1.125 inch.
e.g. https://www.sjscycles.co.uk/gear-spares ... hed-split/
No guarantees though and you probably need to hope that the FD allows more movement in the right direction as well as using the shim.
I'm pretty sure my TA 24T 74 mm BCD inner ring has recessed bolts but that is probably just because it is already rather thick

[9494arnold]

I believe that a "Triple" Front Changer is more likely to have a deeper cage than a double and the "throw" (lateral movement) will be similar.
Are the bolts straight through all 3 chainrings? Have you tried them the opposite way round?

[Brucey]

I would suggest that you use a thinner spacer in the BB. They are commonly needed to fit cassettes onto freehub bodies these days, so are available in 0.7mm thickness and up. If necessary trim the bolts or increase the depth of counterbore for the boltheads in the small chainring (Q; is the small chainring fitted the right way round?).

I note also that if this is a stronglight 99 type chainset, it won't have ramps and pins on the big ring and quite often the FD sees quite a lot of force when making an upshift. This (over time) often deforms the big ring such that it becomes slightly dished in shape, which means that the FD has further to go.

FDs do vary in reach but if you are struggling in the way you describe I would be fairly sure that the chainline is all wrong and that correcting that would be the first choice.

Any photos you have of your setup would be helpful of course.

cheers

[Norman H]

You say that you've cold set the rear end. By how much? And have you checked alignment using the string method?

Also what shifters are you using? Could a mtb front mech be made to work with friction shifters?

[hoogerbooger]

Many thanks all. I took photos but they're pants so I'll have to do again after I've tinkered a bit more tonight:

The inner 28T chainring is on the right way round (which is either way - as it is not an original and doesn't have recesses for the bolt head). The Chainset came with the Revell with 28T, 32T and 42T. It's now set up as 28T, 42T, 50T. The 32T tooth was obviously the original and is recessed ( but a bit worn) I will put it on as the granny and remove the spacer on the BB to check if the front mech will throw the chain to the top ring. At least I'll know something from that....although my missus would still prefer a 28T granny for these Welsh hills. I will no doubt come back and post after.

Some answers to the queries:

Frame was120mm OLN. Is now 129mmOLN (was close enough). .....The hub is a Campag Nuovo Tipo. Presumably originally 126OLN but had washers added to make up to 130mm OLN. Mid spread I tried the wheel at 126 without the spacers. It seemed too close to the drive side dropout to avoid chain rub ( and the rim was slightly off centre). I ended up using different width washers either side and re-centred the rim ( which was fun with 35 year old spokes ) However this will mean there will be just over 1mm offset to the alignment on drive side ( I think ?).

I checked alignment with the string method. It was very close.

Eyeballing the alignment on centre ring and sprocket it's fairly close. I reckon with the 2mm spacer off the alignment would look ok (by eye)

It's on drop bars and 7 speed sti levers

Bolts go all the way through. reversing the bolts might just be enough to clear as the heads are chamferred and the nut end not and the pinch-point is just on one edge....but it would look a bit naff. I reckon with the spacer off it needs less than a mm to clear. However until I've done my tinkering tonight (or tomorrow) I'm not sure if it would solve the reach problem.

Thanks again all.

[Brucey]

a simple way of checking chainline is to offer up a long straight edge to the side of a chainring and see where it falls at the back. This does however still hold the possibility that the BB shell is not set at right angles to the bike centreline.

A piece of string is a really good guide to the track of the frame but it isn't that useful for checking chainline. If the chainline is 5mm out (which is quite a lot) this is only ~0.6 degrees difference in the angle of you string vs the plane of the chainrings; difficult to spot this at all really.

How does the chainline measure from the seat tube?

Note that some frames are designed for a double (or even a single) chainring only; these can have chainstays that occupy the full 68mm width on offer. Frames that fit 'road triples' better tend to have chainstays that are a bit narrower than that.

A good improvment might be to have a machinist produce some counterbores in your chainring.

cheers

[hoogerbooger]

How does the chainline measure from the seat tube?

how do I measure this ? centre of middle chainring to centre of seat tube ? I'll do that as best I can with a steel rule for my report back...( if this is wrong ..say how?)

( not sure I have a long enough suitable edge to do the chain line ....will see)

[cycleruk]

Chainline:-
https://sheldonbrown.com/chainline.html

[hoogerbooger]

chainline to seat tube = 46.5mm ( my best estimate by eye) with the 2 mm spacer in.

I swapped the granny chainrings & removed the spacer . Also wedge the mech out a bit and removed the slack, on the presumption the sti's indexes would then push it out further

.......but not as helpful as I thought as the 32T recessed ring is wider & still jams on stay when fully tightened

So I tightened to just before it jammed and tried the front mech. It just changed up to the top ring, but wasn't enough clearance for it to run without rubbing on the outer face of the cage

Using a 1mm spacer at the BB might improve the chainline ? and just clear at the stay with the 28 mm granny ring.........BUT doesn't look like the front mech will reach the outer ring

Haven't found a suitable edge to check the chain alignment as suggested.

The seat tube is 1.125" .; Is there any chance of some other mech having more range ?

( the one I have looks a bit wobbly and worn, so it may be losing a mm or 2....but when I physically pull it out to its max I don't think it'd be quite far enough if it stayed there)

[Brucey]

if you are measuring 46.5mm chainline (from the bike centreline to the middle chainring) then this is about normal, and I'd suggest that a different FD ought to fix the problem.

cheers