Category Archives: French bicycle

Meca Dural Duralumin Bicycle Frame Construction

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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.

 

When Vintage Components Fail

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While there is no question that the quality of many vintage bicycle components is superior to that of their modern day mass-produced counterparts, vintage components do fail.  Some failures are caused by design flaws, some are simply the result of fatigue and use over the decades, some are caused by improper adjustment or retention, and some by corrosion and exposure to the elements.  How can you determine when it is safe to continue using a vintage component?

Lyotard pedal thread and spindle failure, compared to newer version with longer spindle and more threads.

1950’s Lyotard pedal thread failure, compared to newer 1970’s model on the right.

Sometimes, you can’t.  While I was removing the 1950’s Lyotard Marcel Berthet pedals from a recent project, a small chunk of the threads from the left side pedal spindle simply fell to the ground.  This was after I had taken a test ride, before overhauling the pedals.  What if the spindle had broken during my ride?

Before I disassembled the pedals to examine them, I did some sleuthing.  I wanted to know how one can spot flaws and weaknesses in components before disaster strikes.  I found a good overview of metal fatigue failure at Open University’s Component Failure Museum.  There is a  specific section on their web site for bicycle component failures, including some interesting and scary crank arm, brake, and steel frame failures.  Metal fatigue results in a sudden, catastrophic failure after the initiation and growth of a crack at a stress point.  Is it possible to diagnose such a crack with the naked eye?  Perhaps not if you are not a trained materials engineer.  But, with some basic understanding of cycling mechanics and physics, at least one can know where the highest stress points are for a given component.

In this case, I wanted to know the highest stress point for a pedal spindle.  And, I wanted to know if Lyotard pedals in general, and Marcel Berthet pedals in particular, have had a history of spindle failure.  As it turns out, the answer is YES and NO.  Some Lyotard pedal spindles (namely model 460D) appear to have a history of sudden failure where the spindle breaks in the middle of the thickest part of the spindle, with no warning.  This particular model was ubiquitous in the 1960’s and 1970’s – I have accumulated a number of these pedals in a shop bin.  Some of the cages of these pedals have come apart, or are loose, so I haven’t re-used them and keep them around for parts.  Their spindles all look great, but that, as it turns out, may mean nothing, because the design of the 460D pedals, with their flimsy aluminum cages, may be the actual culprit.  However, the location of the failure on these pedals spindles gives a clue as to their highest stress point, which appears to be closer to the crankarm side of the cage.  Fortunately, I have never experienced a pedal failure while riding.

The highly regarded Marcel Berthet pedals have steel bodies, and shorter spindles than the 460D pedals.  Based on my research, that means they are less susceptible to failure. Steel and aluminum can interact badly with each other over time in a process called galvanic corrosion, so steel cages with steel spindles are a plus.

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The above photo shows the early 1950’s spindles, compared to their mid-1970’s counterpart.  You can see that the manufacturing process changed, and that the newer spindle looks pristine.  On the older spindles, there is brass residue below the base of the cone portion, and I am not sure why.  There are also grooves and striation marks in the area between the brass material and the cone section, as seen below.

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What does this mean?  And, why did the threads fall off upon removal of the pedals from the crank arm?

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1950’s pedal spindle

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1970’s pedal spindle

I think I know the explanation for the thread failure.  The 1950’s spindle has a very deep angled inset at the threaded end of the spindle, whereas the newer version has a much less deep inset.  I think the threads failed simply because there is not a lot of material at the end of the threaded portion.  When the weight of the pedal pulled it down from the crank arm as I was removing it, the threads broke off.  I think the spindles may be just fine, and there are plenty of good threads left to allow re-use of the spindles.  Fortunately, the cones and pedal bodies are still in good shape.

Based on some additional research, I have decided to clean and polish the spindles before reuse, photograph them, then plan to overhaul the pedals with greater frequency and examine the spindles during each overhaul to see if there are any changes to the appearance of the spindles.  While this might seem paranoid to some, it’s my well-being and perhaps that of a future owner of these pedals that is on the line.

Last Sunday, I witnessed a cycling accident that involved a rider on a new (I learned) bicycle.  She was unaccustomed to the quick response and grabby strength of her new braking system – short reach sidepulls – which have a lot more mechanical advantage than pretty much most vintage calipers.  She needed to slow down quickly, applied her brakes, and was propelled over the front of the bike, headfirst.  She was not wearing a helmet, and was pretty banged up.  This was another reminder of the importance of understanding all the elements of the bike you are riding.  Cycling is not the same as driving a brand new high tech car.  All cyclists need to be alert to safety issues involving their components, frames, and riding styles.

1953 French Mystery Mixte Out on the Road

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I decided to take the 1953 French Mystery Mixte out for its first test ride today.  I headed over to Sellwood so I could start the Springwater trail from Sellwood Park, and avoid downtown traffic.  This year, Summer riding in Portland has been a mixed bag.  It has been easy to be beckoned by the dry weather, but the recent heat waves and high humidity have made it challenging to enjoy even my regular commute.  Although cool and breezy, today was more humid than I expected, so my single water bottle turned out to be inadequate.

I was anxious to see how the Challenge Strada Bianca tubular tires felt.  I even wondered if somehow the ride would be transformed by the legendary smoothness and purported supple sidewalls of tubular tires.  I was brought back to reality worrying that I might get a flat.  But, one upside to tubular tires is not having to carry a spare tube, patches, or tire irons.  I can’t imagine what it was like to actually have to carry an entire spare tire (or two, plus glue and a sewing kit).  So, I didn’t even bother with a pump, and just stuffed a few tools and my cell phone into a tiny seat bag.

As I got underway, I felt like I was riding an e-bike. Wait. The bike is long and tall, and  I was in a fairly upright position with the city style bars.  Yet I was positively rolling!  Could it be the tubular tires?  Well, it turned out to be a tailwind, which I discovered when I reversed direction to head back to my starting point on the trail.

After this moment of elation, I concentrated on what the bike was telling me as I sped along, passing nearly everyone:  responsive frame, comfortable saddle, smooth-as-glass hubs, easy shifting, and no lateral flex (thanks to the twin sloping top tubes of this mixte frame).  The tires felt fast, yet more comfortable than similar 30mm width tires that I have ridden, and handled the brief time I spent on hard packed dirt when I took a detour with no mishaps.

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The gearing is very high, and even moderate hills required a standing position to maintain cadence.  I ended up not using the highest gear, and rode the bike as a three speed.  Fortunately, the Simplex Tour de France derailleur can handle up to a 24 tooth cog, which means that the gearing could be lowered from its current 59-83 gear inch range, down to a low gear of 52.  That would help make this bike more versatile.  Even so, hill climbing will remain challenging.

A tubular tire oddity is that they lose pressure very quickly.  They will lose several pounds overnight, and a lot of air after a week.  That’s one reason you’ll see bikes with tubular tires kept elevated, so that no flat spots or creases develop in the sidewalls.  For this outing, I had inflated the tires the night before with about 85 lbs in the rear tire and 75 lbs in the front, but as I was riding I felt sure that I had lost pressure especially in the rear tire.  In the future I will plan to inflate the tires before each ride – which is a good practice anyway.

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I enjoyed using the old Lyotard Marcel Berthet pedals with their original clips and straps.  I hadn’t rebuilt them yet, and even so they performed just fine for this short trip, and were easy to get my shoe in and out of.

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The narrow braking surface of the Clement rims is imprinted with a pattern, theoretically to improve braking.  In practice, the rims emitted a high pitched whining sound whenever the brakes were applied.  While the noise did alert others to my presence, I want to find a way to make braking silent, so will be experimenting with some different brake pads.  I also still have friction in the rear brake cable, which I need to troubleshoot.

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1953 French Mixte at Tilikum Crossing

1972 Mercian

1972 Mercian

Yesterday, I had taken the 1972 Mercian out for a spin, so it was interesting comparing the riding experience of these two different bicycles.  The Mercian is a classic 1970’s road bike, using 700c tires on a small frame which happens to fit me perfectly.  It has a 100cm wheelbase, but similar (and higher than I prefer) wheel flop and trail numbers (wheel flop 17 and trail 59).  I was not disappointed in the handling of the mixte.  I did not have any trouble maneuvering at slow speeds, whereas the Mercian does exhibit the unwieldy feel of a high wheel flop bike when riding at slow speeds. The long 109cm wheelbase helps to keep the bike feeling more stable than it otherwise would. Both bikes are comfortable yet performance oriented, and versatile enough for any kind of riding, with the right gearing.  Neither bike has rack mounts, but both have fender eyelets.  With a saddlebag support, either bike could be put into daily service as a commuter, and the Mixte’s high gearing and light 22 lb weight could allow it to do double duty as a training bike.

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The city style bars have flush mounted levers, which although stylish-looking, means that the only way to adjust the position of the levers, is to adjust the handlebars.  My wrists and hands were uncomfortable after a while, because they were not in a neutral position, so I’ll be making adjustments to the bars as well as completing a few other minor tweaks.

The bike’s first ride left me impressed.  Riding it today reminded me again of how well the cycling industry had developed by the end of WWII.  Its high end components and beautiful Oscar Egg lugs translate into a well-appointed, lightweight bicycle that is perfectly competent and comfortable to ride. I am looking forward to riding it again.