Front mech chainring clearance problem

I bought a road frame off here a few weeks ago and have started building it up. I’ve got one issue I’ve not encountered before which is that the front mech can’t be set low enough on the braze on to be within the proper height above the big ring - it’s about 7-8mm above. My outer ring is 50t, which is obviously a variable affecting the clearance over the mech, but even with a 53t, it still seems too high, based on pix of the previous owner’s build. I’d be grateful for any suggestions for resolving this one. I thought initially maybe a band-on mech below the braze on would work but that would put the mech too low, unless you removed the braze on completely, and I’m not sure that’s a good idea on a Ti frame even if I wanted to do that. Another way could be to get a much bigger outer ring – this may have been a custom frame built for a monster - but this would then affect the rest of the gearing and probably not be the set-up I want, so I am reluctant to go down that route. Is there any kind of adapter to fit to the braze on that could drop the mech 5mm, or some other solution, other than giving up and selling the frame?

Pix:
With a 50t

With a 53t

you get compact-specific mechs these days, I think they are longer to compensate as well as having a different shaped flange (ooh er)

How would that help with the clearane between outer cage and ring?

Well it's designed specifically for bikes with compact chainsets so takes the smaller ring into account, so when I said 'longer' i meant that they are 'lower' from the braze-on.

Oho. I did not know that. I shall make enquiries.... Thank you very much for the lead...

To be fair, most bikes don't need them-I've used compact chainsets without a compact-specific one-so the braze-on on yours must be quite high or just not have a big amount of adjustment.

Coudl well be a factor. It doesn't seem higher than on some of my other bikes but the braze on on my carbon 'Nag gives way more room for adjustment.

There's a couple of threads on YACF about this very problem ... https://yacf.co.uk/forum/index.php?topic=80656 and https://yacf.co.uk/forum/index.php?topic=80928. They drift a bit, but a good few ideas.

I reckon that your easiest and cheapest bodge is to create an extender out of something like an offcut of plumbing copper - might want a couple of thicknesses to keep it stiff enough, but should be able to get close enough to the curvature of the braze-on. Drill a couple of holes, bolt one end to the existing braze-on and the mech to the other.

If that would put the mech too low, then file the braze-on to extend the slot downwards. I reckon you'd defintely be OK if there was 2 or 3mm of metal left at the bottom, and might be fine with less.

Curious: never seen that before.

The only thing that occurs to me, is that the frame pre-dates the introduction of compact chainsets, so the mount is designed for 52/53 tooth rings. It looks to me as is the FD could come a little lower in the second pic: compare the position of the plate and nut on the front of the braze-on.

You do need a compact specific FD, although to the best of my knowledge it is the depth of the inner cage plate that varies, which won't help here. Campag introduced a single STD/CT FD around 2008: I'd be surprised if Shimano didn't also now just have one.

If you were to try an extension, I think you would need two bolts through the braze-on to keep lateral play in check. However, it does look as if the FD would be too low if you sat the bolt below the mount.

I sit a two pence coin on top of the ring to set the FD height: if you do this, where does this put the mounting bolt? Is filing the slot an option?

I've measured a couple of frames and from the centre of the BB to the bottom of the slot is 140mm: what's yours?

Thanks very much for your thoughts and suggestions - much appreciated.
I was thinking of filing down the slot, but the ideal position would mean taking the spot between the bottom of the slot and the bottom of the braze on thus compromising the braze on totally, but I suppose if a bodge as per ^^ was done then it may not affect the strength of the braze on, however, I may as well then get the whole thing removed and stick a band on instead.
It is about 14cm from the bottom of the braze on slot to the bb centre so it doesn't seem abnormal.
I am going to see if I can get a cheapo 53t off ebay and see if that makes for an acceptable arrangement - but then I guess there may be a problem with switching to a 34t inner. Gah.

with my (campag) mechs, I'm pretth sure the compact one has a larger front plate too, I can mosey to the shed to confirm this if you like.

it would seem silly if it didn't anyway, but who knows...

right, all the modern mechs I have are marked as both regular and compact compatible. Drop from center of braze-on bolt to bottom of front face plate is 40mm. from center of braze-on bolt to bottom of the clamping area is 17mm.

the old mech I have that isn't designed to be compact compatible has a drop of 45mm from center of braze-on bolt to bottom of front face plate. from center of braze-on bolt to bottom of clamping area is 17mm.

As Scilly suggests, the difference is in a deeper rear-plate, an older style mech actually has a 5mm advantage for your needs, although I'm wondering if it would be the same if you were looking at touring/mtb or cx mechs that would be designed to go even lower, say 46t?

You've got compact cranks, no? 50t is the largest you'll get on 110pcd.

Speak to your friendly, local framebuilder: as the mount-to-BB distance seems to be standard, my guess is that the move back to band-on FD was prompted by the introduction of compact chainsets....

Personally, I wouldn't bodge some sort of extension; you know how it is: FD always throw themselves into your chainring at *the *most inconvenient times.

As filing the mount isn't practical, I would go for having it removed: should be a quick, cheap job.

Doh! Forgot about that! Yeah, think you're right, will have a rummage on here for frame builders if no better mech can be found.
Thanks folks for being supremely helpful!

Having read this thread, I went into the garage and did some measuring;

I have 2 steel frames from the 90's, pre compact chainsets. The distance from from bottom of the front mech lug to the bottom bracket shell is 115 and 114mm respectively. Both of these frames have been used with 48 tooth outer chainrings without problems. I've also got 2 newer frames with compact chainsets (50 tooth outer) and the lug to BB shell is 105 and 107mm

Useful?

What derailleur were you using with a 48t ring?

I had a Campag mirage on the older frames: 39/48 front, 11-26 rear.

What cranks were you using?

If they were 135pcd that might explain why you could use that ring without issue.

I didn't know you could get such a small outer-ring on a STD crank or such a large inner-ring on a CT.

Not Triomphe/Victory by any chance?

Mirage (non compact) cranks. Originally came with 52/42 but I changed for 48/39. TA replacements IIRC.

• 1 for removing the bracket. But why not do it yourself?
  

Would it be possible to mount a clamp on mech just below the bracket?