bbg

Hi all; got a little pickle here. I over-tightened my clamp and bent the top of my seatpost into an oval. Bike is a ’76 Motobecane Sprint Nomande. Rather than fiddle with the old style clamp & post I figure an easier route would be to update to a one piece sandwich post (although I’d like to keep the bike as stock as possible).

The current damaged post is 24.2cm in diameter which I’ve been told are very hard to source. Anyone have a line on where to find one? Preferably sandwich style but I’ll take anything I can get.

The other option I’ve been told is to utilize a wider post (more readily available) and remove the shim that would make the tube 25.6cm. The only problem is the shim is only a few inches in length and hides the thick inner walls of the tubing that essentially make it 24.2cm the rest of the way down. To provide adequate length for the seatpost the rest of the tubing beyond where the shim was would have to be filed down to widen it. This seems like a hassle and I image the bottom bracket would have to be removed to get all the filings that have fallen down the tube, right?

Please help!

Thanks in advance.

ps: A pre-schoolesque paint diagram to explain “dual-diameter” tubing is attached.

bbg

C'mon gang, I'm in a bind here. Anyone?

Antipodes

Yes, 24.2mm is indeed an odd size. Most vintage rides are 25.2mm and up. Are you sure the tubing changes to the 24.2 diameter further down the tube. For example, a Peugeot UO-8 has some oddball size post - around 22mm or something - but this is with a shim that can be removed, and thus allows you to place a wider post in (like you suggested). I'd be VERY surprised if the tubing is actually 24.2mm. Essentially, the post is only held at the clamp, so the shim only has to be present in this spot. Correct my ignorant behind if you feel so inclined, but I would check down the tube with a torch. A 25.6mm post is a pretty common size and probably easy to find new or used...

JRT

Well, I have a similar problem. I have a 1975 MB Grand Touring and it has the same mickey mouse seat post arrangement. The tube is reamed out at the top and has a shim. My problem isn't as bad because the ID of the tubing is 25.2. Still an odd size and I don't expect to find one soon. So, I purchased a nice NOS Simplex 25mm. I find that high quality masking tape (Scotch Blue) is just the right thickness to keep the bottom end from rattling around. Perhaps something else would be more permanent.

The top of the tub (where the shim goes) at the clamp measures 26mm or 26.2mm ID. Mine also came with a shim for a 24.2mm post. I have not been able to find any metal seatpost shims with 25mm ID. However, Problem Solvers makes 25.4mm ID shims with the needed wall thicknesses (25.4 to 26.4 or 26.6 for the 25mm post or 25.4 to 26.2 or 26.4 for the 25.2mm post) that will probably work after some slight adjustments with a Dremel and a cutoff wheel. The other possibility is simply to purchase the necessary thickness of shim stock since the top flange to keep the shim from falling into the tube is not needed. Do they make .5mm or .6mm shim stock? Is ,02 and .024 close enough? I presume that stainless steel would be best.

I hope that your tube is larger than 24.2 since that size while common on French bikes in the past is not at all easy to find.

bikemore 

For the 25.2 problem, I found a solution from post in the BF maintenance section.
Use a 25.0 and wrap it with a cut out from a soda can. I was pretty shocked
to find that you can cut a soda can with paper scissors and yet it made the
fit!

24.2, I've looked a great deal and haven't ever seen one. Perhaps a 22.2 with
a 1 mm wrap.

JRT

Aluminum shims have a problem. It is called 'creep". They will loosen with time. So, it is better to use a stainless steel shim.

bmaxwell

I got my 24.2 at the schwinn shop they had it in stock... I believe it was a 24.2 I am almost positive that was the size... it was the smallest size they carried... but they had it in stock for under $16.00 it doesn't win any beauty pagents and it is not super lite, but hey it works for holding the seat up.

sfclearwater

I had the same problem with an old Peugeot, it needed a 24mm seatpost. I never did find one so I bought a25mm dimension seatpost and had a machine shop take a mm off.