Editorial Rant - Swagged Aluminum Cranks:
The majority of 3 piece cottered steel cranks ever made have the chainrings or spiders (chainring carriers) swagged onto the drive side arm. See pictures.
Contrary to what some folks want to believe there was never much of a light weight sporting bike tradition in Japan. Keirin track racing is a sport in the sense that horse racing is a sport. The attraction is the parimutuel betting!
During the C&V era most Japanese bikes were 50 lb. single speed rod brake behemoths - a European design dating back to the early 1900's.
Those bikes were used for basic urban transportation (they're still popular in a large part of the world).
Where is this going?
In the 1960's Japanese bicycle component manufactures (primarily Suntour and Shimano) where keen to break into the world market. The US bike boom of the early 70's gave them that opportunity because the European suppliers where hard put to meet the market demands.
Suntour's rear derailleurs set the standard and helped to improve the image of Japanese made components. But... most of those products were made for export not domestic consumption.
Poor quality cottered cranks were major problem/complaint with lower priced bikes during the bike boom fad. The cheap cotters were soft and frequently came loose, especially with strong riders.
There was a call for inexpensive cotterless cranks - both for marketing an performance reasons.
When Sugino, SR Sakae Ringyo and Takagi first started producing low cost aluminum cotterless cranks they didn't have a clue about what they were doing!
They used the same swagging process used on steel cranks. Steel is 2-3 times stronger that cast aluminum plus it's much more malleable; it can be deformed much more than aluminum without braking or cracking.
Japanese in general are smaller in stature than westerners. Most Japanese rode 19"-21" rod brakes.
When larger, heavier westerners started riding those first cranks there was a high failure rate.
I assembled a 1973 Gitane Interclub with a Sugino Maxy crank. When I took it out for a test ride and stomped on it, the pedals spun about a quarter turn. I thought that it was the freewheel tightening up. NO! I spun the chainring on the crankarm!.
We had that problem with all of those Interclubs and it took about 6 months before we got improved replacement cranks.
Pictures show a 1st generation Maxy crank and the problem with the size of the swage on the back side. Compare that with with a larger swagged area on a later model Maxy crank.
As I mentioned in a post above all of these swagged cranks are "melt forged" which is a euphemism fro pressure casting. Because the aluminum casting alloys were weaker than forged alloys the crank arms were made up to 25% larger.
I've ALWAYS considered "melt forged" swaged cranks cheap! By the the 1980's a number of crank manufactures started producing better quality pressure cast cranks with integral spiders.
I still prefer forged cranks!
verktyg
Chas.