Removing Paint from a Bicycle Frame the Safe(r) Way

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Mercier fork

The 1940’s/50’s Meca Dural bicycle that I am currently restoring had an unfortunate encounter with an amateur spray painter.  While this bike’s frame is made from duralumin, a form of aluminum alloy which needs no paint because it cannot rust, the bike’s fork was steel.  When I purchased the bike, I knew it had a number of issues, the horrifically painted steel fork being one of them.

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As you can see from the photos, the spray paint appeared to be hiding rusting and pitting on the fork blades.  While I normally send all paint jobs out to the professionals, feeling that frame painters deserve their due, I decided that I wanted to prep this fork for painting myself so that I could assess the usability of the fork.

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Before venturing out into this unknown territory I did some research to determine what materials and tools I would need for the job.  I ordered emery cloth and wet-dry sandpaper in varying grades, some brass brushes (which will not scratch steel), and a few other items such as tack clothes and dish scrubbers.  All based on advice from Randy at mytenspeeds.com who has done some very nice paint work on his collection of bicycles. I knew that I did not want to use harsh, environmentally unfriendly chemicals for this job.

I fired up my new (non-wimpy) Dremel to use for the hard to access areas near the fork crown, but for the fork blades themselves I wanted to do all the work by hand, the old fashioned way. Unfortunately, whoever painted the fork did so while it was covered with rust.  When I began to remove the paint, I was disappointed to see just how bad the fork blades looked.

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The blades are pitted near the fork crown.  I wondered whether I should try to remove enough material to eliminate this pitting, worrying that I might take too much off and weaken the fork blades.  Then I remembered that fork blades are very thick and sturdy, given the job they must do, so I decided to keep going after observing the very nice brazing done on the dropouts and fork crown.  The fork is well constructed, and deserved my efforts, I felt.

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Cleanly brazed dropouts

While I was working, I was reminded of the bicycle frame that I built, and the effort required to sand the frame and remove excess brazing material.  This is a very similar process.  Using vigorous and speedy strokes with the emery cloth and sandpaper was the key to bringing the fork back to life.  Wearing a mask is a good idea, since you will be creating a lot of dust in the process.

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You can see the progression in these photos.  This process took about 4 hours, and yet  I still need to continue sanding with finer grade sandpaper to complete the work and have the frame ready for paint.  One thing to know:  it is most efficient to sand very quickly, mimicking the action of a power tool.  While my hands are now sore, I am happy with the results, and look forward to the finish work needed before I send this fork off to be painted.

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.

 

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!