I inherited a late 60's Rudge that had been converted into a single speed with 27" rims and racing tires. I've replaced the single speed with an 8 speed internal S/A hub and it works fine. The problem is the chain ring (original Rudge hand) is too large a diameter. As a result the 1st gear ratios are too high.

I'd like to replace the Rudge 7 1/2" ring with a smaller one. But isn't the chain ring welded to the crankset? If so, do I need to replace the complete lower unit? Any suggestions?