guygadois 

I am in the midst of fixing up the old Bertin I rescued the other day. I have two questions.

1) What binder bolt should I use? A literal bolt was used! The binder bolt required has a slot on both sides (see pic). Is there a special binder bolt I should use? Should I look for one slotted on both sides?



2) The seat post size seem small. A 26.8 seems way too big. The tubing is 531. I thought all 531's were 27.2 but I could just be thinking that because all Bob Jackson 531 frames were 27.2. Anyone know what a 531 70's Bertin has for a seat post size?

Cheers,

Gadois

realestvin7

I'm betting 26.2 or 26.4 maybe. Something Frenchy. I have the proper seat post bolt I think.

rootboy 

I'll bet 26.8 or 26.4 is the correct post. It should fit tight. Did this come as a bare frame? Got a vernier caliper or similar? Thoroughly clean out the seat tube of any oils, take some 600 grit wet or dry sandpaper on a 1 inch dowel and clean up the inside of the tube as best you can, even taking off rough edges at the ears of the slot. Clean well, apply a very light coat of grease and re-insert the post. As for the binder bolt, I'd ask the LBS to look through their parts bin. You may find one.

randyjawa 

No - just the bolt will have a catch to fit into the slot. The nut, needing to turn, will just be a nut. The brake cable hanger is slotted on both sides to allow the bolt to be used in either direction. I hope I understood the question, properly.

You need to measure the seat tube cavity and the seat post. Buy a cheap Vernier Calipers and learn how to use them. Measuring diameters is something that is required, from time to time, on any old bicycle build.

verktyg 

Most French bikes used metric diameter tubing... 28mm seat and down tubes vs. 28.6mm Imperial or Inch size tubes.

The standard size seatpost for most metric seat tubes was 26.4mm. As rootboy suggested, you need to carefully clean the old grease and crud out of the seat tube. Also gently spread the ears of the seat lug a little with a large screwdriver or some other kind of wedge. After sanding the inside take a small round or 1/2 round file and make sure that there are no burrs inside the lug.

Before greasing the seatpost check to see if it fits first. I grease both inside the seat tube and the seatpost.

Chas. verktyg