Chainstay clearance - is 1mm too small?

[slarge]

Building up my 1963 Falcon San Remo, and have converted it from cotter pin single chainring cranks to square taper Campagnolo double ring cranks. A 116mm bottom bracket spindle gives a 1mm gap between 42T inner chainring and chainstay - is this too small? I know there will be some flexing when standing on the pedals, but am hoping not to have to buy a 3rd bottom bracket spindle (can't find a 120mm spindle anywhere). Am I going to regret this (the bike isn't ready to ride yet - still building wheels and have some finishing to do, so I can't try it yet)?

Thanks (and if anyone does have a Campag square taper adjustable cup 120mm spindle I would be happy to take it off their hands!)

 

[Old Ned]

Can you not put a thin spacer behind the chainset side cup?

 

[slarge]

Can you not put a thin spacer behind the chainset side cup?

That could work couldn't it - move the whole BB over 1 mm or so. I have plenty of external BB spacers so will try it. I hate taking the cups out of the frame though - chipped the new paint when the tool slipped earlier today!

 

[torqueless]

I have a similar issue- SR Royal cranks on a Dura-Ace BB (112mm?) on a frame with no dimpling in the chainstays leaves me about 1mm clearance too. I may be wrong but I don't think it is about flexing- I can't imagine anything flexing that much within four inches of the BB spindle.. If there were to be any contact, it would be a result of either play in the BB bearings, or foreign matter building up on the back of the chainring/bolts creating a sort of accidental grinding paste that eats away at the chainstay as you turn the cranks. So.. scrupulous cleanliness and maintenance down there is essential, even if only to find out if the bits can flex enough to make contact.

 

[Midlife]

SJS and others do a range of generic ISO square taper axles of varying lengths . Not campag but might he OK.

 

[slarge]

Using an external bottom bracket spacer (approx 2mm) on the drive side between frame and BB cup has sorted it - it moved the chainset outboard by 2mm and gives 3mm clearance. The non drive side still had enough spare thread for the lockring, so all is good. Torqueless - this should also work for your DuraAce bottom bracket. Thanks all

 

[torqueless]

Might be a bigger can of worms for me- Single speed, so I have to consider my chainline. Also I have this thing about maintaining equal(ish) crank/chainstay clearance drive and non-drive side- probably irrational, but if it makes one happy..

 

[Old Ned]

Might be a bigger can of worms for me- Single speed, so I have to consider my chainline. Also I have this thing about maintaining equal(ish) crank/chainstay clearance drive and non-drive side- probably irrational, but if it makes one happy..

You could fit a similar width spacer behind the sprocket. Sprocket thread and BB threads are same size.

I think............

 

[pigman]

You could fit a similar width spacer behind the sprocket. Sprocket thread and BB threads are same size.

I think............

I always like the maximum threads interface on the rear hub. Half a thread screwed onto half a thread risks the hub thread stripping when applying torque during riding

 

[torqueless]

Yeah I'll take maximum threads interface anywhere I can get it.. In my situation I wouldn't think of respacing more than 1mm. But, like the OP, I don't even know if I have a problem.
The way I see it, as far as chainstay/chainring proximity is concerned, "A miss is as good as a mile", provided that it carries on being a "miss".
None of these strategies are particularly appealing:
1)Pull apart an A1 condition Dura Ace 7400(?) BB and replace the axle with a longer generic one. (Note to self- try and work out which bits are ISO taper and which are JIS taper in advance)
2)Use spacers and reconcile oneself to mismatched crank/chainstay clearances and compromised thread interfaces.
3) Put an indentation into drive side chainstay of forty-five year old 531db frame.