What tubes did Moto used on pre-73 Grand Record? The OD seat tube is 28.2mm and it takes a 26.6mm seat post. Thanks

probably 28.0 tubing sans paint. Those are French "metric" sized 531 butted tube measurements.

Look https://www.classicrendezvous.com/Fra...obecane_Hm.htm, too

Also depends on how/whether the seat tube was reamed after brazing.

That's pretty thick paint .2mm. Is that why a lot of early moto have little cracks all over their paint?

Actually that makes it only 0.1mm since it's on both "sides" of the tube

I'd guess metric 531, why would it be in doubt?

Just seem kind of odd, that the measurement was 28.2 instead of 28. My Grand Jubile with Vitus 172 measured at exactly 28mm. Didn't know what Moto used in their early Grand Record.

I don't know about about pre-1973 but the 1973 definitely spec'd butted Reynolds 531 and that's the correct post size for the metric version of that tubeset. Agreed, the variance is a little thick for paint but it could be a tube on the high side of the tolerance, unclean jaws on your calipers, etc. or a combination of any of the above.

Hey one man should not talk about other man's caliper like that. T-mar, do you have any idea when M'becane switched their logo from the plastic pentagon head badge to the circle head badge? I am trying date mine. My guess is mid 60's to early 70's.

I always thought it went the other way around; from the circular metal badge, to the plastic pentagon. I guess I'd better go back and check some of catalogs and advertisements.

The round head badge was to commemorate their 50th anniversary, which was in 1973, but I think it didn't actually appear on bikes until 1974.

Well, I went back though my old catalogs and magazines. It appears there is some variation in headbadge styles, depending on the model. However, I did find a single example of what appears to be arbarth's style of head badge in a a 1973 road test of a Le Champion. Unfortunately, its a hind quarter pic, but the badge is definitely very thick, with a flat top and long, straight side. I also have an early, undated, catalog showing a Grand Record with a sticker headbadge. From what I've read, Moto was not nationally distrributed prior to 1972, so the catalog is probably a 1972 or 1973. The round headbadges were in use in 1974 and the 1975 Grand Record definitely had a round headbadge. Since the only evidence of this style of headbadge is from 1973, I'd say abarth's model is probably a 1973.