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.

Welcome Home, Centurion

Here is lovely 1975 Centurion Semi Pro.  It has been well preserved over the decades by its original owner, and I am now the proud steward of this extraordinary machine.

As readers of this blog already know, I have been on a decades long quest to replace my crashed 1976 Centurion Pro Tour, a bike which was my only bike for over 20 years, and upon which I logged over 40,000 miles including tours of the Pacific Northwest, the San Juan Islands, and Canada, as well as serving as my daily commuter.  The Pro Tour was my original all-rounder.

So, when I saw this baby blue 1975 Centurion Semi Pro on eBay, I knew I would be honored to shepherd this bike into its next phase.

When the bike arrived, I unpacked it like a toddler with a new toy, and when I found these interesting frame transfers, they confirmed the information provided by the seller of the bike (who was not the original owner, but who sold it on their behalf).  The first human to ride this Centurion was a member of the US Cycling Federation (now known as USA Cycling), and had ordered the full Dura Ace upgrade for this bike, as well installing racing tubulars instead of the 27″ clincher rims offered as standard equipment.  The original owner was also a member of the League of American Wheelmen and had added these black and white racing flag transfers to the top tube.

While the bike clearly had a documented racing heritage, I was puzzled to find the Dura Ace crankset mounted with a chainguard.  And, you’ll note that the rings are not in racing configuration, but are a compact set-up with 52 teeth on the large ring and 39 on the small ring.  Both rings are Shimano Dura Ace.  Don’t forget to notice the lovely Dura Ace front derailleur.  The Dura Ace upgrade included:  the front derailleur, the anodized brake calipers, the drilled levers and the crankset:

These Dura Ace components are in amazing condition.  The drilled levers look new, but are given away by the gum hoods which have long ago lost their resilience.  The brake calipers are beautifully anodized.  The Dura Ace crankset with its 172.5 arms is in equally amazing condition, considering its 43 years in service.

I enjoyed seeing this unusual Huret wrap around chrome cable guide which provides shifter cable routing on both sides of the frame. This bike has zero braze-ons.  While it is built with Tange Prestige #1 tubing, during this era braze-ones were rare, and most needed accessories and cable guides were handled via clamps.

SunTour Mighty ratcheting downtube shifters

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Shimano Crane GS drilled long cage derailleur

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SunTour GS chromed dropouts with single eyelet and adjuster screws

The drivetrain consists of SunTour ratcheting Mighty shifters mated to the Dura Ace front derailleur and a Shimano Crane GS rear derailleur.  The Crane would be needed to handle the 52/39 rings up front.  The dropouts are by SunTour, and I don’t think I’ve ever seen anything as lovely as these fully chromed SunTour GS dropouts.  Their unusual shape made me look up this component in the SunTour catalog.  You’ll note that the design pushes the dropouts inward toward the hub.  I wonder if this simplified mitering the rear stays.

The pedals also provided a surprise – they are very rare Barelli Supreme pedals, with the optional alloy cages.  According to the site Classic Lightweights, these pedals “were considered the Rolls Royce of pedals. The spindle was made from Nickel Chrome Steel and they were machined for accuracy at the bearing surfaces and they came with a life time guarantee”  That, and the other component upgrades help to explain why this bike weighs in at 22 lbs.

The upgraded wheelset consists of 27″ Super Champion Competition tubular rims laced to Sunshine Pro Am low flange hubs.  A new set of Pararacer 20mm tubulars were installed as part of the deal.  I’m not sure how well the new tubulars were glued, so I will probably install a clincher wheelset on hand for this bike’s first test ride.

The bars were upgraded to 3TTT, mated to a Cinelli stem.  The original SR seatpost looks beautiful with this Cinelli leather Unicantor saddle.  Unicantors were the first plastic base saddles of this era.  I haven’t ridden one before and look forward to trying it out.  You’ll also note the Centurion’s impressive, chrome wrap around seat stay.

This Semi Pro has the following SN:  M5J00027.  Consistent with all Centurion frames I have encountered, and as documented by others, the first letter indicates the frame builder, but no one knows who that is.  Since both my 1976 Pro Tour and this 1975 Semi Pro start with an “M” I will guess they were both built by the same manufacturer, probably Japanese.  The second numeral is a “5” and that indicates the year built – 1975 – which is consistent with the bike’s components.  Another way to date a bike without a reliable serial number is by the components.

Some readers might wonder about the photos in this post.  For the most part I used my Panasonic Lumix mirrorless camera, but I also brought out my Leica Digilux 2 for some of the photos seen here.

I look forward to venturing out on this extraordinary bike, and will keep you posted on our progress.

And, here are some related technical and historical documents:

1978 Centurion catalog (the 1975 catalog does not seem to exist online) – vintage centurion site – http://vintage-centurion.com/literature/centurion-catalogs.shtml

1975 Shimano Dura Ace – disraeligears site – http://www.disraeligears.co.uk/Site/A_Complete_Line_of_Shimano_1975.html

1976 SunTour catalog – Velobase site – http://www.velo-pages.com/main.php?g2_itemId=12472