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Old 01-12-19, 03:58 PM
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Originally Posted by Aubergine View Post

Weird. It looks slightly pinched in spots but a bit open at the very top. Given that you can insert the long post so far, I would cut that post shorter and use it without worry. Three things to do: measure the “minimum insertion” length and make sure that you leave at least that length for insertion in the frame after cutting; chamfer the bottom edge of the cut post; use plenty of grease when you put it all back together.
The post is a really heavy poor quality steel one with some rust. I'd like to get something a bit lighter weight. The current one is also the clamp around the tube style, and definitely not original.

Originally Posted by Prowler View Post
I don't know if this helps as Motobecane was evolving to ROW standards during the timeframe. Dimensions year to year can be different. My 1979 Mirage is made with 2040 straight gauge steel. My seat post is 25.4mm and the ST OD is 28.3mm which includes the paint. I doubt I could get a 26mm post into my frame.

Can you find a machinist who can measure the ID of the seat tube, a few cm below the seat tube top lug? That would "learn ya" some good data.

Get a good flashlight and inspect the ID of your seat tube. Ensure there is no ridge which is blocking the post from fully inserting. My winter project is a 73 Grand Record. It's stem wedge had rusted badly and left a ridge on the ID of the steerer. The stem would not insert past the min insertion point. I used a ball hone which did not help much. Quality time with a round file finally removed that ridge and the stem fully inserts now. Any obstruction in your ST?
The OD of my seat post tube is 28.35 including paint, etc., so it must be different. That's interesting, I'll have to grab the tools from work or take my frame with me to grab the ID a few cm down from the top.

I'll also check for obstructions. Either way, I don't want to use the old seat post, but want to locate a new, correctly fitting one. It seems like a great and easy place to cut down the bike's current weight.

So far I've got in the following parts:

NOS 22mm Motobecane branded SR 22mm stem
Jagwire road pro cables and housing
New SRAM chain
Charge Spoon brown saddle

Still plenty left to get, but it's coming along. I spent a little time cleaning and degreasing the frame last night. With a little polishing compound some of the hazy look of the paint is clearing up nicely. I need to get some touch up paint and clean out all the small rusty rock chips next.

Last edited by Cheseldine; 01-12-19 at 04:03 PM.
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