The crank arms weren't dated until '73.
Sounds like you had a spider that was at one end of the machining tolerance range, plus a pin that was on the long end of it's tolerance, plus perhaps a slightly bent (or "adjusted" by someone) spider, chainring, or both. Things can stack up, and anything is possible with old parts that have already lived a long life.....
I measured a whole bunch of Record / SR cranks once - and even within a "bump-size" group, the distance between the outer 'ring and the back of the RH arm varied about +/- 1 mm, (and remember that the difference between the two types is only 1.5 mm nominally), so there are manufacturing tolerances at play there, plus the afore-mentioned "tweaking" by owners / mechanics over the years.
For spacing, there are only two kinds of vintage Record arms - big bump (early, 1958-1977) and small bump (late, 1977-1987). Note that both occurred in 1977. All "big bump" ones need the early spindle (112/113) and all "small bump" ones need the late (114.5/115.5) spindle. That's the key to understanding this issue. (we're talking road cranks here, BTW...).
Regards,
Greg Parker Dexter, Michigan
P.S. For anyone that may be curious (and isn't bored to tears yet), the "bump" is the area on the back of the RH Record crank arm, right around where the BB spindle inserts into the arm. Once you've seen both types, it's clear how to easily and quickly tell them apart.
Date: Mon, 13 Dec 2004 04:03:23 -0800 (PST) From: Jerome & Elizabeth Moos <jerrymoos@sbcglobal.net> To: gpvb1@comcast.net, classicrendezvous@bikelist.org Subject: Re: [CR] Outside chainring for 151 campy crank - Now Chainring peg
Thanks, Greg. A bit of a mystery here. I had replaced the large chainring on the obviously non-original 1975 NR crankarm on my 1973 Paramount, as the chainring that came on it was a bit scratched up. Even though, per someone's answer to my question here a couple of weeks ago, Campy started dating crankarms in 1972 or maybe 1971, this bike, built in January 1973, had an undated left arm. I figure this is probably original, especially in light of what you say about the size of Schwinn's inventory, so I bought an undated right arm that Eric Elman was offering recently.
Here is the mysterious part. The pin had been fine on the 1975 arm, but when I removed the '75 arm from the bike and transferred the ring to the undated right arm, the pin pressed up against the inside of the undated crankarm. I had to file it down to make it fit. This would imply that the 1975 arm had more space between spider amd crankarm than the undated one. Yet conventional wisdom is that this change was mandated by 1976 CPSC regulations and didn't appear until the 1977 crankarms. Don't know what to make of this.
Regards,
Jerry Moos Houston, TX
gpvb1@comcast.net wrote: As I mentioned earlier today, 1974ish is my guess. 50-tooth and larger only. My 1973 Paramount didn't have one either, but also don't forget that Schwinn often bought five- or ten-year supplies of Campy parts at a time (think big, be big, think big, be big...)!!! Not a CPSC thing, IMO - too early to have been that, plus, it's not really a safety-related issue. (of course, neither were all of the actual CPSC-mandated changes in 1977, so maybe that isn't such a good analogy)! The length of the pin didn't change in 1977 - it just leaves a slightly bigger gap from then on, with the later-style arms. Greg "no-peg rules!" Parker Ann Arbor, Michigan Date: Sun, 12 Dec 2004 13:51:27 -0800 (PST) From: Jerome & Elizabeth Moos To: Joe Bender-Zanoni , "Thomas L. Hayes" , classicrendezvous@bikelist.org Subject: Re: [CR]Outside chainring for 151 campy crank - Now Chainring peg
Speaking of Campy rings, does anyone know what years the Campy NR large rings were made with the peg on the ouside that kept the chain from falling between the spider and the crankarm? I thought these were on the early NR cranks, but my 1972 Paramount doesn't have it, while my 1984 Trek 6600 does, and I think both chainrings are original. Was this a CPSC thing?
Regards,
Jerry Moos Houston, TX
Joe Bender-Zanoni wrote: Yes and yes. The smallest ring was 44T. The track rings had an extra reinforcing rim around the inside of the ring. They were very substantial. Also the track rings were available in one inch pitch. Sugino made a lot of track rings in 151 BCD and they do not have the reinforcement.
Joe Bender-Zanoni
Great Notch, NJ
> What was the smallest (least number of teeth) chainring designed as the
outside ring for a Campagnolo 151 pattern crank? And was there a specific
chainring designed for track cranks that differs from their road chainrings?
>
> Thank you.
>
> Cheers.
>
> Tom Hayes
> Chagrin Falls, Ohio