Just when you think you've seen all the odd things done by Schwinn, or TA, or Raleigh, you discover yet another. As related below I was reassembling the original TA Cyclotourist chainrings I took off my 1973 Schwinn Sports Tourer when I discovered that the holes in the 54T outer ring for the inner and outer chainguards seemed to be identical to the holes for Criterium rings, i.e. the outer ring seems to be drilled for both Cyclotourist and Criterium inner rings, except the Criterium holes were used for the chaingaurds instead. This probably makes sense, as AFAIK, the Cyclotourist outer and the non-adapteur Criterium outer ring were identical except for the BCD of the holes for the inner rings. So TA would have had machine tools set up to drill the rings at both circles, and the easiest way for them to fill Schwinn's order for chainguards would have been to simply drill both circles in the same outer ring. It would be interesting to know if they ever sold those double drilled rings to anyone besides Schwinn and if they ever produced them in any size other than 54T.
Yesterday, I finished reassembling the original rings using spacers from my parts bin, as I had used the original spacers on the replacement 50-36 rings I installed on the bike, although I was unable to use the original bolts because the replacement 50T outer had countersunk bolt holes. After finishing reassembly, I discovered that there was not enough clearance between the inner ring and the inner chainguard to prevent the chain rubbing. Evidently, when addding the inner chainguard, Shwinn had been forced to use thicker spacers than the standard TA double spacers to maintain chain clearance. It suddenly occurred to me that the use of the extra thick original spacers without the chainguard on my replacement rings was the cause of fairly frequent problems shifting down to the small chainring. Until then, I had thought the 50-36 spread, the same differential as the original 54-40, was simply too large, and that Scwinn had known what they were doing in adding the inner chainguard to "guide" the chain onto the small ring.
Today, I pulled the small ring off the bike, and sure enough, the spacers from the orininal rings with chainguards were much thicker than the standard TA double spacers, nearly twice as thick. So I switched out the spacers, installing the standard ones on the replacement rings on the bike, and restoring the thick ones to the original 54-40 rings with chainguards. Now the 54-40 has chain clearance between the inner ring and inner guard, and the problem shifting down to the small ring on the bike seems to have disappeared.
So while the Schwinn engineers made shifting to the small ring easier by using the inner chainguard, at the same time they made it more difficult by using thicker spacers. Difficult to say whether the OE design worked better or worse than if they had done nothing and just used the standard TA setup. But of course In The Day, there was the right way, the wrong way, and the Schwinn way, and Schwinn of course usually went with the latter.
I find that I also have a Nervar Sport crank, which in fact was more common on the Sports Tourer than was the TA on mine. It also has inner and outer chainguards, but they attach differently from those on the TA and I believe it would be possible to change ring size on the Nervar while retaining the guards. This crank is also 54-40, and I think it is near certain that it is also from a Schwinn. If and when I use it, I'll probably change to smaller rings but keep the guards. But if anyone intends to remove the guards forn such a crank, it might be wise to check the spacer thickness. If they used extra thick spacers like they did on the TA, then one might need to install standard spacers at the same time one removes the guards.
Regards,
Jerry Moos Big Spring, Texas USA.
Jerome & Elizabeth Moos <jerrymoos@sbcglobal.net> wrote: On my recently rebuilt 1973 Schwinn Sports Tourer, I replaced the original TA Cyclotourist 54-40 rings with 50-36, which IMHO make more sense on a touring bike. Unfortunately, the new rings cannot mount the unusual chainguards.
The original rings had chainguards for BOTH the outer and inner rings. The outer guard was presumably to protect one's pant leg from chain grease and perhaps to prevent the chain dropping off the outside of the crank if the FD was improperly adjusted. The inner chainguard evidently was to prevent the chain dropping between the two rings, which could easily happen with the very wide 54-40 gearing.
Today, I reassembled the original rings and guards before I lose any of the parts - if I had thought ahead, I would have just removed them from the arms as a unit.
Examining them more closely, both guards are bolted to the outer ring through a single set of holes. There is a spacer between the outer ring and the outer guard to space the guard out from the ring. But there is no spacer between the outer ring and the inner guard, rather the inner guard bolts flush against the inside of the outer ring, as it must to leave clearance for the chain to engage the inner ring. This means the outer ring must be sufficiently large the the chain engages it at a radius great enough to clear the inner guard. Looks like the outer ring must be at least 46T, maybe 48T.
Measuring the BCD of the chainguard holes in the outer ring, they appear to be at the same 151 or 152 mm BCD as holes for a Criterium inner ring. Indeed, the hole diameter seems the same as well, so that one could attach a Criterium inner ring in place of the chainguard, but with different length bolts. Note that there are two types of Criterium "outer" rings. When using a Criterium adapteur, both outer and inner rings are of the same type, with a 151 or 152 BCD. But when the adapteur is not used, the Criterium outers ring attaches to the arms at the same very small circle as the Cyclotourist rings, except that the Criterium outer is drilled at 151 BCD for the inner rings, rather than at 80mm as is the case with a Cyclotourist. Now, although I don't have a TA cyclocross chainset, I rather suspect that for cyclocross, one used a Criterium outer, but mounted the cyclocross chainguards on either side of the ring, using the 151 BCD holes that would otherwise be used for the inner ring.
But for a wide range road double like the original crank on my Sports Tourer, one needs and outer ring with three sets of holes: The very small BCD set for attaching to the arms, the 80 BCD set for attaching the inner Cyclotourist ring, and the 151 BCD set, identical to the drillings for a Criterium inner rinng, but used instead for the outer and inner chainguards.
Anyone ever seen such a triple drilled TA outer ring, other than OE on Schwinns? Anyone ever seen such a ring smaller than 54T? I'd like to restore the original chainguards, both because I think they look cool, and also because the inner one probably does really help prevent dropping the chain between the two rings. But I'm not willing to tolerate a 54T outer ring.
Regards,
Jerry Moos
Big Spring , Texas, USA