I’ve finished my re-interpretation of this 1975 Centurion Semi Pro, with today’s late fall Pacific Northwest sunshine providing warmth and dry roads for its first test ride.
After purchasing the bike a few months ago, I disassembled it, assessed its frame and components, and then re-built it as a city commuter, to reflect the kind of riding I currently enjoy. The frame was free of rust, and in unusually nice condition for its age. This Centurion Semi Pro had been upgraded at original purchase to Shimano Dura Ace components and a 27″ tubular wheelset.
I kept as much as I could of the original Dura Ace components, but I knew that I would replace the wheelset, not wanting to ride on 27 inch 20mm tubulars through downtown Portland. At first, I considered a 650b conversion as the best option for adapting this bike to my riding style. But, the close clearances on this frame designed for 27″ wheels meant that I was looking at an 87mm brake reach to accomplish the conversion. While possible, this amount of reach is not ideal. There are brake calipers which have enough reach to accomplish the conversion, but they are not in my constellation of desirable components. Instead, I converted it to 700c, using the existing anodized Dura Ace calipers, which had plenty of reach for a 700c wheelset.
And that wheelset turned out to be one that I had built a while back and which I had used on my old Davidson: Campagnolo Record 36 hole hubs built up on new Mavic Open Pro rims. The blue rim logo picks up nicely on the Centurion’s sky blue frame paint. The tires are Panasonic Pasela 700 x 35. They have a tread pattern which is different from all other Pasela tires. The big tires on 700c wheels make for a tall bike, which I noticed throwing a leg over and while riding in its new upright position. Being visible is a plus for cycling commuters.
For the modifications to convert this bike to city use, I selected some of my favorite components: a Stronglight 99 crankset with 48/37 rings, a SunTour gold 14-32 freewheel, SunTour bar mount ratcheting shifters, Dia Comp brake levers, and french Sufficit grips glued to a steel Northroad bar. Most useful was a NOS Jim Blackburn rear rack with its single stay attachment to the rear brake bridge – a great solution for bikes without rear rack mounts.
When I was selecting and testing components, the original Shimano Crane GS rear derailleur presented some problems: the amount of tension needed to shift to larger rear cogs was significant. And that tension helped to explain the scratch damage on the frame from the shifter clamp moving down the downtube. I found that the original Shimano Crane GS rear derailleur was not performing as expected. I disassembled the derailleur (thank you RJ the bikeguy) and found that the springs and pivot bolts were caked in grime and dirt. However, after cleaning and lubrication, the Shimano Crane derailleur still requires a significant amount of cable tension to move the parallelogram. Shifting the bike today on its test ride required overshifting on the up shifts, and a lot of adjustment on the downshifts. I expect that I will probably replace the Shimano Crane with a SunTour derailleur to improve the rear shifting.
When I ventured out today, I planned on riding my usual route around my hilly neighborhood. I enjoyed getting out for a ride on this Centurion Semi Pro. There seemed to be almost no interference between my crank inputs and the bike’s outputs. The ride was smooth and effortless. The way back home to my house involves choosing among several different routes, varying in difficulty. With this bike’s easy pedaling, I chose the most difficult route home, one that I have dubbed the “TDF” route, with its cobblestones and steep inclines. That’s a route I only ride on my ALAN or Guerciotti – lightweight and high performance bikes. So, even as converted to a city style bike, this Centurion Semi Pro has impressed me.