A "Patent" chainring is pre-1976, I believe.
I have a 1974 Raleigh International (1973 date-matched grouppo) which spent most of its life in a garage in Santa Cruz. The bike was hardly used - with original tape and one original tire (RALEIGH NYLON EXTRA.)
Every square inch of this bike was covered with rust. There were 1x1mm rust pimples on each square inch of the framset - coming through the unscratched paint. Both chainwheels had extensive damage from the saltwater air. The damage was :
- tiny 1x1mm bubble that rise off the face of the chainwheel. The bigger ones would "travel" kind of like spider veins on a leg.
- on the inside edge of the chainwheel, the rifling in the anodization layer allowed the saltwater corrosion literally to begin to splitting the chainwheel apart, by lifting up the aluminum (up to 5 mm in from the inside of the chainwheel ) in a line going straight towards the outside of the chainwheel.
Other aluminum parts (derailleur, weinmann brakes, etc.) were not affected. The unpolished parts (seatpost, hubs, pedal barrels) were not too badly pitted.
My theory is that there was probably something about campy's nickel / anodization finish that causes the chainwheel to be susceptable to saltwater air.
- Don Gillies
San Diego, CA