sunburst

I'm restoring a Moto mixte and the previous guy put in a 25.4mm post. It seems like slightly small because you have to completely close the gap in the seatpost slot to keep it from rotating. Yet, when I remove it and pry the gap open, I have to use what seems like too much force to insert a 25.6mm post. Btw, this was a heavily modified bike, with SA 3-speed IGH with 700c rims, single chainring, no FD, dual pivot brakes, a mtn bike seatpost, strange bars, mtn bike levers, etc. I've restored dozens of French bikes but have never seen one so far from stock. And the serial number is close to impossible to read. Makes it hard to date.

So, given all that, anyone know what diameter seatpost Moto used, in what appears to be an late 70's mixte? The new buyer wants a silver one and I'd hate to order the wrong thing and perpetuate the error.

juvela

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there are so many things which can affect this fit:

seat lug/seat tube out of round due to brazing heat

corrosion of interior walls

foreign matter such as paint and/or dirt

deformation caused by over tightening of binder ears in the past

suggest to prise apart binder ears

then run an expandable blade reamer through

not for the purpose of enlargement but to get the hole round and free of any foreign matter

if bicycle were earlier could give size estimate from experience but have not worked on any MB's as late as your example

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sunburst

I could not find an appropriately sized blade reamer and/or did not understand the choices, so did not pursue that, although that sounds like the best approach. Coincidentally the only other time I have heard of this tool/solution is with installed a guitar peg/jack for a pickup.

I had a long 25.6mm suspension post that I could insert a few inches. If it had been solid I think I could have cut it down and had a good solution, or if I had a very long reamer. As is turned out I found a 25.4mm on an old Raleigh that was very close and with a thin seatpost shim seemed very solid once in place. And that in-turn provided the impetus to order a setback seatpost for the Raleigh that I have put off for many months, which solves a bike-fit issue with the short rails that Brooks uses.