Join Date: Jul 2004
Location: On the border between the Space and Treasure Coasts of FLA.
Bikes: Schwinn WorldSport, Takara,
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I started to convert the Sugino crank on my Schwinn World Sport to a triple back in 1998. It already had blind holes cast in for the third ring. There were complications! Drilling the holes to the proper size for tapping. I was able to do this on an industrial drill press with a drill press vise at work. I consider this neccesary to keep the holes at 90 degrees to the plane of the chain ring. Finding a 8mm x.75mm tap! Had to order one through a friend who runs a machine shop. Then, had to grind the point off the tap so it would cut threads sufficiently deep in the spider. Now, to keep the threads perpendicular to the plane of the chain ring!! Back to the drill press and vise, put the tap in the chuck and TURN IT BY HAND to the proper depth, repeat four more times. Now that all the hard work was finished, I bolted the ring to the spider only to find the spacing between the middle and small ring are to close. I never did get access to the material or lathe to make spacers. In the end, I bought a Sugino triple crank arrm. It doesn't match the original, but, you only see one side of the bike at a time!!
Have a skilled machinist lay it out and do the work. The ring will be concentric with the crank and you'll have fewer grey hairs. I'd have never attempted this if the original crank did not have the blind holes cast in the spider.