[CR]Re: Put the lime in the coconut etc

(Example: Events)

From: "Stephen Barner" <steve@sburl.com>
To: <classicrendezvous@bikelist.org>
References: <CATFOODFsCrNdZQQL6A00000f11@catfood.nt.phred.org>
Date: Sun, 16 Nov 2003 17:54:42 -0500
cc: rdf1249@aol.com
Subject: [CR]Re: Put the lime in the coconut etc

There is at least one other difference in the spiders for the Campy triple cranks. The spider arms have a little less taper in them, ending about 2mm wider at the thinnest point than the standard double arm. This makes the arms just a little wider at the point where they are drilled for the extra bolts, presumably to help make up for the lost material at the hole. This observation is from comparing a '73 triple and a '73 double.

Still, I agree that this isn't the point where the greatest stress is, and I wouldn't be averse to having a double drilled to accomodate a triple ring. Muscling up the gaps around here in a 42x26 can really sap you for the rest of a ride. I may take you up on your offer, Bob, and have my spare double arm drilled.

--Steve Barner, Bolton, Vermont. wading through 6" of snow.


----- Original Message -----


> Date: Sun, 16 Nov 2003 05:12:14 EST
> From: RDF1249@aol.com
> To: classicrendezvous@bikelist.org
> Cc: mpetry@bainbridgeisland.net
> Subject: [CR]Re: Put the lime in the coconut etc
>
> > Right Steve - Jon hjertberg of wheelsmith had these jigs for a while -
> > there may have been other sets as well. I could think of a way to do it
> > with a lathe too. I know several people who have ridden cranks so
> > modified. But it scares me a little bit, given what we already know
> > about the failure modes of Campy crankarms. The factory campy NR
> > "triple" arms had slightly thicker arms in the spider where the
> > intermediate bolts went thru, and those arms had a threaded bushing to
> > mount the inner ring. The modified arms simply use a bolt that threads
> > right into the aluminum.
> >
>
> Sorry to disagree, Mark. The Campy #818 triple bolt/spacers are threaded
> into the aluminum of the crank arm with no such bushing. Stop by and see a
> couple on my bikes. There is a difference between a factory and a drilled triple
> though. That is that the milling on the front of each arm of the spider stops
> short of where the triple bolt hole is, so the arm is indeed thicker there.
> That said, I have done dozens of them over the years with no failures. Campy
> cranks do fail, in the crotch near the arm, at one end of the arm milling or
> other, and sometimes at the pedal threads, but I have not had one fail at the
> triple bolts. I have though seen triple bolts themselves break in a drilled
> crank. I think it is from failing to counterbore the holes a little to give
> relief to the triple bolts which have a slight radius at the end of the threads.
> If you don't counterbore for this, then the bolt doesn't sit flat against the
> crank arm and can get wiggled back and forth so it fatigues. I have a jig
> that we had made many years ago for accurately drilling and tapping Campy cranks
> for a triple, and I do counterbore them. It is almost a moot point though
> because you can't hardly find the Campy #818 bolt/spacers any more. I have a
> stash of Avocet (ofmega) bolts and spacers that accomplish the same thing and are
> not so sensitive to the counterbore problem, since the bolt and spacer are
> two pieces. I have offered this service to the list before, and at the risk of
> being called on the carpet for it, I will just say that the door has been
> reopened and people may not have known that I do this. I charge $30 per crank arm
> plus $15 for the bolts and spacers. It will take any 74mm chainring,
> although some have to have their holes reamed to fit. A tapered reamer does this
> easily. Send me your tired, your poor, your dirty old Campy cranks and let me
> turn them into a nice old man's triple. I have a couple favorite chainring
> combos by the way. I use 32-42-47 and 13-26 freewheel on my old touring bike with
> a Campy front derailleur and short arm Campy NR rear derailleur and it works
> great. One my "vintage" titanium bike though I use 32-42-52 and 13-26, with a
> Suntour XC Pro front derailleur and a NR rear with Rally cages to suck up the
> extra chain. Those both be factory triples with Merz 32T rings that were
> made for Campy triples.

>

> Bob Freeman

> Seattle