Sizing a Campag square-taper BB

[drossall]

We've been fitting a Campag square-taper BB to s-i-l's classic TT build:


However, the axle is plainly too short:


We measured the axle as 111 end to end. Our LBS, which is very good, tried a 115, but said that was much to short. We're a bit baffled as we'd have thought that it would just about give enough clearance. Cue daft question; I'm not totally clear whether the entire difference would be on the RH end, or whether some of the extra 4mm would increase clearance on the left crank. That's not too bad even with the 111:


The chain line is also a bit left of ideal, but not too far out (again, like all pictures, with the 111mm BB):


So, should we try another 115 and, if not, can we find a longer one? I don't think the 177.5 cranks are helping of course! It's a classic Campag track set, which I gather was quite widely used on 90s and similar era TT bikes. And we do realise that we need the right taper.

All thoughts welcome! NB the cranks were only fitted by hand with no bolts, so when tightened they'd be a fraction further in.

[zigzag]

it looks like there is a track chainset installed which has a different chainline to a road one (3-4mm difference). ideally a road chainset should be used on a geared bike.

[Pickled Onion]

What zigzag says ^^^

I'm fairly sure the campag BBs are symmetrical, so a 115 only gives you an extra 2mm, and the chainline is way, way more than 2mm off what you need. If that's 135mm OLN then that would have matched with a 111 + triple or 115 + double - off the top of my head, someone will be along to correct me shortly  . Either way, and even if it's not 135 OLN, use a chainset from a geared setup with a single chainring and you can put the ring either side of the spider it will work with any BB.

[Brucey]

for some weird reason I don't see your pictures.  But anyway, do check, but IIRC the 'old' Campag taper (which is pretty close to JIS in fact) hung on in the Pista components long after the road stuff all migrated to ISO. If so, that could be the problem here.

IIRC the old NR and SR pista BBs used a 109mm spindle (old i.e. non ISO taper).  At that time if you butchered a road crank (to remove the shoulders that support the inside chainring) I think it gave the same chainline in the big ring position as a proper Pista crank. This wasn't always optimal for a single-ring TT derailleur setup; if you favoured the smaller sprockets a chainline 3-4mm further out might be better, and for this, one of the (many different possible) road double BB spindles might be a better option.

cheers

[LittleWheelsandBig]

It is an ISO BB. Are the cranks bottoming on the axle ie. Do you actually need a JIS taper?

I'd try another 115 BB, Campag if the cranks look to have proper engagement with the taper. I'd think hard about fitting a driveside spacer on the BB to improve chainring clearance.

[drossall]

Thanks all, yes, a Pista chainset; s-i-l tells me it was common practice on TT bikes. I should remember but don't; it rather passed me by as I rode the same Zeus double for a decade or more.

We'll recheck for bottoming out.

[drossall]

He's trying a 90s double. We'll see how that works out.

[Rhys W]

ISTR that Campagnolo made two different 111mm BBs like that, a symmetrical double and an asymmetric one intended for their triples at that time. I could be wrong though.

I run one of the 111mm doubles with a mid-90s Chorus crankset (with a single chainring) on my SS conversion. Worked out pretty much perfectly, luckily for me.

[alexb]

It does ring a bell that there were two types of Campag BB's one for road doubles and one for triples.
You might try HubJub for advice, Geoff Butler and Bike Plus always had a good stock of Campag BB's and Mercian have a good reputation for knowing their way around all things Campag.

[Biggsy]

Below Chorus: both double and triple chainsets were designed for the symmetric 111.  There was also a 115.5 for triples with fat seat tubes for extra front mech clearance.

Record/Chrous: 102 for doubles, asymmetric 111 for triples.