A 1975 Centurion Semi Pro

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.

1975 Centurion Semi Pro in original configuration

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.

Campagnolo Record quick release skewer, SunTour GS Chromed dropouts with adjuster screws and single eyelets.

Mavic Open Pro 700c rims

Campagnolo Record hubs

Pasela 700 c 35 mm tires

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.

Blackburn rack with single stay attachment to the brake bridge

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.

13 thoughts on “A 1975 Centurion Semi Pro

    • Good question! The current front clearance is only about 6mm, which is the distance between the bottom of the fork crown and the top of 35mm tires. This is one of those vintage bikes that has more clearance on the rear than the front. So, with the 35mm wide tires as installed, it would not be advisable to mount fenders, at least not on the front in the traditional way. One idea would be to used the “over the top” method by cutting a set of fenders and using brackets attached to the rear bridge and fork crown to mount the fenders. Or, it might be possible to take a hybrid approach, mounting the rear fenders in the usual way (which have about 11 mm of clearance), and cutting the front fender and mounting it over the top. The other option is to reduce the tire width substantially so that fenders can be mounted under the bridges in the traditional manner. But, that would reduce the bike’s versatility over a variety of terrains.

  1. I also echo Ryan’s question on fenders but mainly wanted to commend you on taking a bike traditionally paired with drop bars and bringing yourself upright. I’ve done this before on a few bikes now and have been pleased with some results, others, not so much.
    I do hope you post a follow-up on how the refresh goes as you spend some time in the saddle. Inquiring minds want to know!

    • Thanks, Josh. It was interesting to take this bike out on its first ride in its new upright position. Its racing heritage was obvious as I made my way uphill with the bike responding beautifully. I am not the kind of rider to tuck in on the downhills nor worry about top speed on descents or flats. But there’s really nothing like riding a one of kind bike such as this, whether it be for commuting, or just meandering around! I did have some pedal strikes on my rear Jandd grocery bag used on the bike’s maiden voyage, due to its shorter chainstays. Fortunately, there are plenty of narrower pannier options available, such as smaller offerings from Ortlieb.

  2. It looks like you will have many miles of enjoyment out of this bike. The set up seems comfy for the type of riding you do. The beauty of the older frames is that they are very adaptable to various aplications. A note on the 27″ tubulars , I was told that tubulars have always been actually 700’s even though some were marked as 27″! I found this out when I recently purchased the Paramount rims that were supposedly 27″ tubulars, they are 700’s. Joe

    • I think that might be right! The wheels originally spec’d for the bike were 27 inch, but the tubular rims which were an upgrade ordered by the original owner, may have been 700c.

  3. Another beautiful build – you’ve given me ideas for my ‘79 Centurion Pro Tour!

    I know you’re “not enamoured with half step gearing,” but if you happen to have the same 14-32 freewheel I have (14-17-21-26-32), then you have the possibility of creating one of the most ideal half-step drivetrains possible. Traditionally paired with 50/45 chainrings, you have nearly identical gear ratios for every step. To handle your TDF route, add a third 28t ring and you’re golden. Of course, you don’t have to double shift every time if you don’t want, the large steps are good for hilly terrain (as I’m sure you know).

    • Hi David, I do have that same Suntour freewheel. It’s been “interesting” going back to a 5 speed wide range freewheel for commuting. I actually don’t totally hate half step gearing, but it is not a good option for bikes used for commuting, which require multiple and frequent shifts even on a short ride. For touring and long rides, half step gearing makes a lot of sense. I have duplications in my gear set-up with the current configuration, and so I’m losing about 1/3 of my gears to dups. Since this is a 10 speed set up that is significant. To correct that I am going to use a smaller inner ring, which will provide more even steps throughout the gear range and will eliminate the duplications. I’ve been trying to avoid going to a triple, not that there’s anything wrong with that 🙂

      • Nola,

        I totally understand that point of view. I live in the mountains, but our valley that is nestled between them is relatively flat so MY town bike is actually only a 5 speed. Any hill I can’t handle with that bike is short and gets walked up. 🙂

        Good idea on the chainring changeup. I think you’ll get great mileage out of a more “compact double” than your initial chainring choices and, as you mentioned, eleminate many duplicate gears. Take it all the way down to a 28t and conquer nearly any hill! (16t gaps up front are NOT the limit with a properly sized chain.) Besides, going wide without needing a separately sized ring is one of the unique benefits of those old, out of production 86 BCD cranks – I love mine! And you can avoid a triple… not that there’s anything wrong with triples. 😉

      • I have come to appreciate the 86 bcd cranksets such as the Stronglight 99. The versatility in chain ring sizes makes for a useful option for many different applications.

  4. Great article. I am planning on doing some modifications on my 1977 Fuji S12-S LTD racing/touring bicycle to get it ready to ride all over my hometown state, then United States. Wish me luck!

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