unworthy1

sure looks like an Allegro to me. No clue as to why the "serial number ingot" (I like to call it a lozenge) is missing, but I know no other brand/marque that checks these boxes.

jPrichard10 

After seeing all the evidence, I agree. And maybe it did have the seat tube replaced?

Because the big mystery for me still is why are there so many stamped numbers on the bottom bracket? I'm curious if other Allegros (never seen one in person) have anything stamped into the bottom bracket, other than what was originally cast. If it was stamped sometime later, it seems strange to stamp it three times, in two different directions with three different size and type of stamp.

But I also can't imagine some other Swiss frame builder copying an Allegro so perfectly.
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rustystrings61 

So I went trawling stuff and learned that Reynolds 531 seat tubes had wall thicknesses around .8/.5 mm (some places say .8-something/.56 or so. So that looks well within the realm/range of being reamed out to take a 26.8 instead of the expected 26.6, and @juvela gives two good reasons why that happened.

Over on the framebuilder forum, Mark Bulgier wrote -
"The two systems are too far apart. Neither metric tubes in inch lugs, not the other way 'round, will result in clearances suitable to brazing.
The smaller socket can be milled or reamed to fit the bigger tube, as with putting a 1-1/8" tube into lugs or BB shell that were originally 28.0 mm*. But with a metric frame, there ain't no way to put in a 1" TT, since that's smaller than the existing 26 mm TT. No way to shim it and get a strong enough joint IMHO, the tube is just too small.

So now I wonder if the seat tube was replaced at all, or if the serial number "ingot" was just removed during renovations. When I went back and looked at the thread from when this bike surfaced here, when it was still believed to be a Peugeot, I looked closely at this image, the only one I have seen from the non-drive side of the top of the BB shell -


- and I think I am correct in saying there is NO BB shell oil port there. The number stamped onto the underside of the BB shell, 194741, would have been used by Allegro during the period when they fitted oil ports, something discontinued between no. 230908 and no. 233385. So the number may be a red herring. If it is indeed an Allegro, and I think that it is, the lugs say 1961-1974, the lack of an oil port says c.1972-74, the lack of chrome says likely left the shop with the grade C parts but was still functionally identical to the ultra fancy Special models with smoked paint and chrome. I strongly suspect now that the original serial number ingot was removed when the fender eyelets were shaved and the brake cable tunnels and bottle bosses were added and it's likely that it still has it's original seat tube, just reamed out to take the 26.8 mm post.

Were this one mine, I'd start looking for a 531 fork with a Vagner PL crown, strip it, paint it, decal it as an Allegro and ride it lots. Had my old one actually been my size, I probably would still have it. My perception of my last one was that it floated over the road and felt a lot like a long wheelbase early PX-10 with more trail.

jPrichard10 

I happen to have a 531 fork, but not the right for crown and with Imperial oval blades (assuming Raleigh). That might be what has to go in the frame unless I get lucky.

The plan is to repaint and decal it as an Allegro, but unfortunately not to ride it. I am much too tall for this one.

bulgie 

Well they made different thicknesses as well, such as one very close to 1.0/0.7 mm that was very popular with OEMs.
Back then they were all made to wire gauge numbers which don't always match up well with tenths of a mm. So the 21/24 gauge tube is very close to .8 in the butt, but the unbutt is .56 -- actually closer to .6 than to .5 mm.

Seat tubes are almost always single-butted, on butted frames, so it's the .56 mm part that we have to fit a post to. With the normal amount of heat-distortion, we usually fit a 27.2 mm post if it's 1-1/8" (28.6 mm), or 26.6 for a 28.0 mm tube. But with careful low-temperature brazing (less distortion), plus a little reaming, it's definitely possible to mount a 27.4 or 26.8 post.

But R also made 531 plain-gauge tubes in 0.8 mm, which for 1-1/8", take a 26.8 post "natively". So just knowing the seatpost size doesn't tell us which ST is in this frame.

-Mark B

droppedandlost 

Something else to look for, mine has stamping on both sides of the seat lug

jPrichard10 

This is helpful, and while I can't see any markings through the paint, there might be some signs with the paint removed.

And I'm sure you would have said, but there's no frame size stamped between your chainstays on the BB shell?

unworthy1

I think (at least the RH) are just Nervex (angle and socket numbers) so nothing to do with frame maker. Also the OP's uses Bocama (BCM) type 14/11 lugs so won't have any Nervex numbers. Not sure about the "A 77" (?) on the LH side, that could be stamped by Allegro I suppose

droppedandlost 

correct, no size stamp

bulgie 

The angle marking on the right and the "A" on the left were stamped there by Nervex, not the framebuilder. The "77" is not a Nervex marking though. Maybe the year? Could your frame be a 1977?

droppedandlost 

serial number 167974 places it in 1960

bulgie 

Yeah I figgered 77 probably wasn't the year; Nervex lugs were pretty unpopular by then. (I still like 'em though!)

So what the 77 means? Might have to remain a mystery. It sure ain't the seat tube angle

juvela

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77 might be identification mark of builder

or of quality control inspector

[wylde speculation ]


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