Mark Petry's Primer:
Some Cool-To-Know NR/SR Facts..
(from the Classic Rendezvous mailing list 11/16/99)


- There is a date stamp on the back of 1973 and later NR/SR cranks. A number in a diamond represents a year in the 70's that the arm was made. A number in a circle represents a year in the 80's that the crank was made. Either "11" or "22" in a box represents a production run, probably mid 80's that was pretty much the last of the NR/SR stuff. Perhaps some of these late items were warranty stock? Don't know for sure...

- 1978 was a big year of change for NR/SR. CPSC mandated that the front derailleur have a "lip" on the leading outer edge so nobody would impale themselves on it - Never mind the big aluminum disc with sharp teeth - or Huffy's!

Now we can tell the true NR/SR BB Road Spindle Story!

To accommodate the CPSC front derailleur lip, the distance between the arm and spider of the crank had to be increased, which then meant that the bottom bracket had to be lengthened too! The result is that the arms were redesigned - older pre- CPSC right arms can be identified by a relatively large bulge of relatively larger diameter on the backside where the spindle enters. Later arms have a smaller bulge of smaller diameter. The changeover was in the 1978-79 period. Early cranks use bb spindles with markings such as 68ss x 120 or 70ss x 120, while the later cranks use slightly longer spindles that are marked simply 68ss or 70ss. Some transition era spindles carry the designations such as 68ss x 120 AND have +1 /+1.5 markings to the side of the 68ss x 120 or 70ss x 120 stampings. That means that the spindle is the same as the later ones without the 120 designation. Use of a later crank on early spindles usually caused the crank to hit the frame. Use of the later spindle on an early crank pushes the arms out farther than optimal - but if using on a 6 or 7sp, or if the arms are worn, then the chainline error may be minimal - this combo may in some cases even be better.

THE UPSHOT is that the 120 designation does not, for practical purposes, refer to rear frame spacing - the issue to worry about is era of crank.

Use of derailleur with lips on early cranks is a leading cause of grooves being worn on the backside of the drive arm. Keep those lips off our early cranks!

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