Meca Dural Duralumin Bicycle Frame Construction

Meca Dural bottom bracket shell

From the 1930’s through the 1950’s, the French were enamored with aluminum bicycle frames, even though steel was the material of choice for most builders.  A number of examples still exist today, and after disassembling and cleaning this 1940’s/50’s Mercier Meca Dural frame, I can see why.  The bottom bracket shell is a work of art, looking as if it had been machined yesterday, rather than more than 6 decades ago.

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I became curious about the method of joining the aluminum tubes with aluminum lugs, using what I had read were internal steel expanders.  Apparently, at the time there was no method to “glue and screw” the aluminum tubes, a method that was pioneered by ALAN beginning in the early 1970’s.  The only joining methods which were available then were gas welding the tubes – a process used by Nicola Barra; connecting octagonal aluminum tubes into aluminum lugs with connector bolts – a process used by Pierre Caminade; joining the tubes with aluminum lugs and wedged internal expanders – the method used by Meca Dural, and other other hybrid methods involving pinning the lugs, and using a steel rear triangle.

When I passed my magnet over the frame, I picked up no attraction, except for a very faint pull near the lugs.  You will note that the chain stays and seat stays are connected with a combination of bolts and aluminum sleeves, and that the bottom bracket shell is held in place with two large bolts connecting the lug to the chain stays.  The aluminum sleeves do double duty as the brake bridge and chain stay bridge.

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The seat tube/seat stay lug is pinned, as you can see above.  But what about the main tubes – how do the internal expanders work?

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As it turns out, it was fortunate that the Meca Dural headbadge was missing, which allowed me to peer into the head tube lug to examine the expander inside.  My magnet told me that the expander is steel, and the method to accomplish the expansion process seemed to involve a steel tab which was probably manipulated with a special tool.  When you think about it, the same idea is used for quill stems inserted into threaded steerer tubes.  That seems to have worked pretty well, so why should these lugs be any different?

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At first I wasn’t sure of the purpose for the large holes underneath each of the two headbadges.  Upon closer examination, you can see that the head tube and head lugs are actually machined as one piece.  The holes are necessary so that the expanders can be inserted to join the top tube and down tube, necessitating a hole for each tube.  And that is why there are always two headbadges on every Meca Dural frame -to cover these holes.  That’s one mystery solved.

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One thing that seems true of older aluminum frames is their flexibility, relative to steel frames.  My ALAN is a very flexible frame, but not too flexible.  I guess you would say it is flexible in the right kind of way.  To satisfy my curiosity about this frame’s flex characteristics, I squeezed the rear dropouts to test the amount of flex.  Then, in my unscientific experiment I compared the amount of flex on this frame, to all the other bare frames hanging in my shop, all of which are steel, and some of which are Reynolds 531.  I was able to flex the dropouts on the Meca Dural about 7 or 8 mm, using my weaker left hand at full force.  On several mixte frames, I could barely move the drop outs 3 mm, and on a diamond vintage Reynolds 531 frame, I could flex the drop outs about 6 mm at full force.  That’s a significant difference in flex, and it will be interesting to see how this frame rides once I have it restored.

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With just some minor polishing with a wadding cleaner (I use NEVRDULL), the frame shines beautifully.  I need to source some 650b wheels from the period, because at some point someone tried to install 700c wheels on this bike, and that is how the bike was configured when I acquired it.  The spacing at the rear dropouts is 115 mm, so it would be hard to find the vintage hubs to build a wheel set, even though I have a nice vintage set of rims.  Instead, I am on the hunt for a donor vintage bike from the 40’s or 50’s which can give me a decent 650b wheelset, and maybe a few other parts to add to my collection.

 

A 1940’s/50’s Mercier Meca Dural

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This French Mercier bicycle has captured my attention.  It is made from duralumin – the same stuff blimps were made with – by Meca Dural using a unique procedure to join the tubes with aluminum lugs and wedged steel internal expanders.  The Meca Dural company produced aluminum frames from the 1930’s through the 1950’s on behalf of a number of cycling manufacturers, Mercier being one of them.  A Mercier Meca Dural is included in the Embacher collection (which was sold in its entirety at auction, earlier this year).  The blackbirdsf site also has photos of a variety of duralumin frames of various manufacturers, including Aviac and Barra, as well as Meca Dural.

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This Mercier Meca Dural is a “ladies” bike with a step through frame, although it is not a mixte frame as it lacks the set of extra chain stays typically used to stiffen the frame.  Depending on many factors, this may or may not be a good thing.

The bike features a Stronglight crankset with 46 teeth, CLB 700 brakes with useful and ingenious quick release mechanism, Atom hubs, Samir Saminox 700c rims, Huret plunger/pushrod derailleur, a 4 speed freewheel, and a serial number on the left side rear drop out – 16822.  Here are some photos of the components:

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Huret derailleur with plunger/pull chain mechanism – for 4 speed freewheel.

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Stronglight 49D crankset

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Tank pedals

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Atom hub with Huret wingnuts

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Very nice CLB 700 brakes

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Mercier headbadge, with upper round Meca Dural headbadge missing

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Crankset lettering – Louis Verot chainring with 46 teeth, bottom bracket connector bolt

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Rear drop out with SN 16822

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Beautiful lug design which includes cable routing braze-ons

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Ideale Leather Saddle, Model 80

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Alloy porteur bars, CLB Guidonnet levers, Sufficit grips, Luxor headlamp, Dural Azur stem

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Luxor 65 headlamp

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Samir Saminox 700c steel rims

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Bottom bracket lug, joined below with bolts

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Hammered Le Martele Lefol fenders, hammered rear lamp.

Mercier fork

Steel fork with lugged chrome fork crown, amateur paint job, Stronglight headset

The bike has a number of issues which will affect the restoration process.  The steel fork was horrifically spray painted gray  – so the paint will need to be removed.  Upon closer examination, I have concluded that the wheels are not original to the frame.  There is a 1975 date code on the Atom hub, and not only that, their diameter suggests that this bike was built for 650b wheels and not 700c – the fork crown and rear brake bridge daruma bolts foul the 700c tires.  Clearly the bike was built for 650b wheels, which I confirmed after measuring the CLB 700 brake reach.  And, some features are missing –  the fenders show that the bike originally had a rear and front rack, and the fork mount dynamo is absent, as well as the original chain guard.

Even so, I am looking forward to restoring this machine and to its first test ride, as I want to experience the feel of the aluminum frame and steel lugs, and to judge the frame stiffness for myself.  Stay tuned!

Early 1950’s French Mystery Mixte, Part II

1953 Oscar Egg Mixte

I have dated this bike to the early 1950’s.  It is most likely a 1953 model, given the “53” code on the Fratteli Brivio (F.B.) hub cones, the “53” code on the Regina 4 speed freewheel, and the Simplex Tour de France rear derailleur, which matches visually to photos of other TDF models I have located dated as 1953 models (and includes a few features not seen on the late 40’s models).  However, there is also a “51” code on the Melas fork mounted dynamo, but an earlier date code for a component such as this doesn’t necessarily indicate the bike’s date of creation.

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Oscar Egg lugs. Note the small diameter tubes.

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I say “creation” instead of “manufacture”, as clearly this unique mixte, with its Oscar Egg lugs, was a custom build.  Unfortunately, there is no headbadge, nor are there logos of any kind present on the frame.  However, some barely visible white and orange paint artifacts still remain on the seat tube indicating the presence of transfers which have either faded or were removed.  And, on the headtube there is a shadow of what was once an oval or triangular sticker.

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The fork is likely not original to the frame.  Its brake reach is 7 mm longer than that of the rear brake reach, necessitating the use of longer reach Weinmann 810 sidepulls on the front (with the rear using a Weinmann 730).  In addition, the downtube shows evidence of a front impact, further supporting my theory that the original fork was replaced.  The fully chromed fork, although in beautiful condition, is not as nicely finished as the rest of the frame, with crude file marks still visible on the inside of the fork crown lug.

The use of a longer fork than original means that the headtube angle is slacker than originally conceived.  I measured it at 68 degrees, compared with the 71 degree angle of the seat tube.  According to this helpful guide from Damon Rinard, you can determine the effect of using a longer or shorter fork on your bike’s original frame geometry.  Conclusion: even fairly large length differences don’t matter all that much.  An 11 mm difference in fork length only changes the head angle by .64 degrees.  In this case, the slacker angle increased the wheel flop a bit, but the trail measurement of 58 mm and the wheel flop of 20 mm are still well within the normal range.

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Ideale TB 14 Saddle

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City style Scheeren bars, highly polished, with original grips

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Clement tubular rims

 

Fratelli Brivio (F.B.) hubs

Fratelli Brivio (F.B.) hubs

This bike is a study in contrasts.  It is built with top end, very light components.  As pictured it weighs only 22 lbs.  The use of the very best hubs available at the time laced to the Clement tubular rims indicate a rider who wanted speed and comfort, and was willing to pay for it.  The timeless Marcel Berthet Lyotard pedals include Christophe toe clips and leather straps, further evidence that the bike was meant for spirited riding. On the other hand, it has slack geometry, city style bars, and a heavy, but comfy Ideale TB 14 saddle.  It is also a larger mixte frame, measuring 55 cm x 55 cm, with a very long 109 cm wheelbase.  Although there are single fender eyelets front and rear, there are no rack mounts.  When cleaning the bike, I found evidence that a rear saddlebag support had been clamped on the seat stays.

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The Regina drilled 4 speed Model Fulgur 15-17-19-21 freewheel was an especially nice bit to find on this bike. The teeth show no wear, and with a little oil and cleaning, it looks and sounds brand new.  Some freewheels, such as SunTour and Regina, emit an incredibly pleasing sound, and this one is no exception.

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Simplex TDF rear derailleur mounted to the model specific Simplex drop out

After setting up Simplex TDF plunger/pushrod style rear derailleurs more than a few times, I have finally got the hang of it.  For this build,the derailleur responds extremely well and shifts as quickly as any modern derailleur, without any over shifting required.  Fortunately, I had the original chain, so I was not left to guess about chain length, and I think that helped a lot.  The new chain is a bit longer than I would have cut it if I had not had the original.

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Titan seatpost, gold lined lugs

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Favorit PWB (Prague Warsaw Berlin) crankset

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Highly polished stem, bars, and headset.

All of the components had been highly polished, even the Weinmann sidepull calipers.  Cleaning them was very easy.  The frame took more work, as there was a heavy layer of gunk over the paint.  The resulting sparkle was well worth it.  I was very surprised at how nicely even the silver paint on the stays cleaned up.  The bike really does look impressive.  An unusual feature is the curved rear stay, to allow the brake cable to lay flush against the frame.

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Curved rear stay

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Through the frame wiring for the fork mount dynamo, not yet installed.

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Flush mounted levers, Scheeren bars, Phillipe stem

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Simplex shifter with helpful cable stops

This was one of those bikes that I wanted to keep as original as possible.  However, the frayed brake cable housings had to go, as they were not usable.  I have a stash of vintage cable housing in various colors and from various periods.  I have found that this silver colored housing which I believe dates to the 1960’s has a really nice vintage-y look.  I had a length that was in good condition, so used it to replace the brake cable housing.  I decided to keep the shifter cable housing original.  Although the outer casing is cracked in areas, far less forces are exerted on shifter housing and the interior coils were fine, so I lubricated the original shifter housing and installed a new cable, which had to be sanded down a bit in order to fit into the Simplex shifter mechanism.  I did not install the Melas fork mount dynamo – it had probably failed long ago and was not useable.  I hooked up the pretty rear lamp, and will now try to source a fork mount dynamo from the period which has an integrated head lamp.

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I have yet to test ride the bike and to experience the tubular tires, the mounting and gluing of which not only expanded my knowledge (and possibly fried my brain), but made me feel glad to live in the era of high performance, supple clinchers.  Back then, tubulars were really the only option for comfort and performance.

I’ve got some friction in the rear brake cable, and I suspect I’ll also have a bit of noisy braking when I venture out.  So, there’s more effort still to make in getting this bike back on the road. It will be interesting to see how the bike rides, given its contrasting features.