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Zach

Well I hope that this is not the case. The top tube looks to have a slight bend and the end of the top lug sits up a tiny amount.

I just started putting it back together last night Sad

Thoughts?

Gold

sandranian · Site Admin

Those being the original forks, you should check for a corresponding bulge in the down tube, or some sort of bend in the fork. Usually, that is from a front impact. However, Gitane bicycles were not always the "cleanest" builds, so it may have been an imprecise alignment when it was built, and it wasn't caught by quality control because they were selling bikes faster than they could make them!

Again...look for corresponding bends, bubbles, or paint cracks.

Zach

That was the only spot. I checked over the rest of the bike and it is fine. From the looks of it the lug is the only issue since I might have found a "bend" since I was looking for one.

I hope the guy that built it was just having a bad day.

BTW who made the lugs for Gitane? The fork looks to say Nervex

sandranian · Site Admin

Probably a "bad day". My Super Corsa had the same issue.

They used a few suppliers. Chas. knows this type of stuff...but I know that Bocama made them for some. Look for the "BCM" stamp on the head tube lug (bottom one).

Zach

Yep. BCM on the lower front lug.

verktyg

Zach,

It looks like maybe the top tube was cut a smidgen to long or not mitered properly.

When these tubes are heated enough to melt the brass they're very soft and the slightest pressure, say from the frame jig will cause them to bend like yours. It's hard to see under the heavy layer of melted flux covering the lugs etc. until it's sandblasted.

It might not have been noticed (if at all) until the assembly line. During the Bike Boom manufactures were pushing bikes out the door as fast as they could box them up.

QC? What's QC?

You shouldn't notice any thing in the ride unless the head tube angle is steeper than about 75° then it might be pretty twitchy.

Chas.

vanhelmont

Zach,

I don't think you have a bent tube. Lugs come in a limited selection of angles, so sometimes the tube intentionally doesn't go in straight. On my frame it is most noticeable where the down tube goes into the bottom bracket, but also on one of the head lugs. There was also a place in one of the head lugs that wasn't filled with brass, but when I stripped it I could see that the weld was good, it was just a small area right at the surface that wasn't filled. But your gap is pretty big. It may also be some mis-cutting like Chas says.

If it was bent there would have to be some bending somewhere else in the frame, most likely at the lower head lug, and it doesn't look like there is.

Dave

verktyg

The Bocama top tube/head tube lug is stamped 72° on this frame.

Bocama lugs came in 71°, 72°, 73°, 74° and 75° angles with the appropriately angled bottom tube/head tube lugs. Top tube/seat tube lugs were available in the same angles.

For whatever reason most bike makers tried to maintain the same overall wheel base length for all of the frame sizes in given model. This resulted in some squirrelly handling bikes in the extreme small and large size frames.

Two other flies in the ointment:

1. Tubing manufactures provided tubes in standardized lengths, the 3 main frame tubes were usually around 60cm or 23"-24" long.

2. Bike manufacturers usually only used lugs in one angle, 72° or 73° for most frame sizes. Gitane's choice was 72° during the late 60s and early 70s. Mid range bikes were 72° "parallel".

Ideally larger frames should have slightly longer than standard top tubes while smaller frames, shorter top tubes to fit the riders body sizes.

Maintaining a uniform wheel base length created smaller frames with very long top tubes and larger frames with short top tubes.

In addition, some larger frames with long top tubes tended to have steeper head tube angles to push the rider's weight more forward while small frames had shallower head tube angles to allow for toeclip clearance with the front wheel with shorter top tubes.

Steeper seat tubes will add a little more rigidity to the rear triangle while more slack angles provide a little smoother ride.

Most lugs in those days had a lot of slop in the fit and tubing could easily be moved a degree or two in the lug.

I seem to remember the larger Gitanes had 74° or 75° head tube angles.

I briefly owned an early 70s Gitane Gran Tourisme. It was an oddball frame size, 53cm center to top (52 C to C), Gitanes were 50cm or 54cm. It had a 69° head tube and a 71° seat tube with a long top tube. The best description was that it handled like a wheelbarrow! Two or three rides and it went on the wall for sale!

So getting back to Zach's bike, it could be that when the frame was being brazed, it was meant to have a 74° or 75° head tube angle using a 72° lug. Maybe the worker didn't push down the lug point while it was red hot.
Too much wine for lunch!

Chas.