tsappenfield

Again, thinking about rebuilding the 1975 Raleigh Professional frame I acquired last summer. I need a seat post so I can attach the frame to my bike stand. I used a pair of Verneir calipers to measure the inside diameter of the seat tube and it appears to be 26.5 to 26.6 mm. What size seat post do I need? Anyone know the identity of the seat post that originally came with the bike?

TSAPP

norskagent

Should be 27.2mm

orangeology

according to mr.brown's old raleigh page:
https://sheldonbrown.com/retroraleighs/professional.html
it says originally campy record. (table at the bottom of the page)

however, his seatpost size database page doesn't list professional.



(hey, btw. pls don't get me wrong. i'm studying myself here too)

MetinUz

+1

cudak888 

Are the seat lug ears pinched at the top?

Metric 531SL is the only explanation I can think of for an SBDU frame with a genuine 26.6 seatpost inner diameter, and I cannot recall ever seeing a 531SL SBDU frame - metric or otherwise.

-Kurt

tsappenfield

Before I measured the inside diameter of the seat tube, I tried inserting the seat post from my (non-vintage) road bike. It's a 27.2 mm Ritchey and it definitely does not fit. Perhaps I could REALLY grease it up and force it into the seat tube, but I don't think that's the way it should work. Is there some "rule of thumb" for selecting the seat post size, i.e., 1 mm (or whatever) less than the inside diameter of the seat tube? I don't think the seat post ears are pinched.

TSapp

bibliobob

531 was sometimes 27.0, though I don't know if Pros ever came this way? My Competition is 27.0...

Photos please!

MetinUz

Could we see a closeup of the seat lug, taken from back side? I am guessing that the ears are pinched, you will need to straighten them before you can insert the proper seatpost.

Ex Pres 

My '78 is definitely 27.2

tsappenfield

I'll get a photo up this evening.

TSapp

T-Mar

+1 regarding the lug ears. The other (more remote) possibility is that it may be a Reynolds 753 frame. They would use a 26.6mm post. It would also be easy to verify, as they used the 28mm outer diameter, metric seat tube versus the imperial tube with a 28.6mm outer diameter.

tsappenfield

It's Reynold's 532 and not 753. Picture coming soon.

TSapp

delicious

Just adding to the chorus: my '76 is 27.2

Ex Pres 

I'm kind of hoping you have a metric-tubed 531 Raleigh Pro. That would an excellent thing to add to this forum. Of course many pictures would be required.


Edit: dang, just pinched ears

tsappenfield

Here are the photos. Thinking ahead, if the ears are pinched, what then, i.e., how does one "unpinch" the ears?

TSapp

rhenning

Put a screw drive into the slot and widen the slot is the way to widen a pinched frame. There is no such thing as Reynolds 532 that I have ever seen. Roger

tsappenfield

I stand corrected. It's Reynolds 531. (Must put my fingers on a diet soon.)

TSapp

tsappenfield

I haven't heard an opinion yet. Are the ears pinched?

TSapp

USAZorro

Question for you. What's the serial number on the frame? I am asking simply to attempt to rule in/out some possible explanations. The ears do not look badly pinched, however if the top of the seat tube is ovalized a little bit, it might be at some point other than at the ears. Another thought (pure speculation) - the frame might possibly have been built with the butted end at the top, rather than the bottom.

cudak888 

That's not an SBDU frame - it's a run-of-the-mill Raleigh Professional Mk.IV. Hence, it is 27.2 - unless it is a strange/botched build from the factory, which is unlikely.

At any rate, those ears are pinched - even the seattube hole itself has been ovalized. You will find that you'll have to very carefully spread the ears more than necessary in order to widen the flattened areas enough so that the 27.2 can fit again - then, while the post is in place, fasten the overspread ears. The tube will re-conform to the post.

-Kurt

T-Mar

Very good point. It's been known to happen.

As to the ears being pinched, it's very hard to tell in the provided pictures. Shadows, focal distances and parallax can often create an illusion of things that don't exist.

There's a lot of shadow in the picture taken fromm the top, but the slot does appear to be parallel. If the post was 0.6mm undersize, the slot would be should be about 2mm narrower at the top. For your typical slot, that would be about a 50-66% reduction and should be clearly evident if you compare the bottom to the top.

However, the opening also appears to be very oval. In the pic, the front to back dimension appears to be about 10% bigger. If the post matches the width, and the opening is oval, there should be a discernible gap in the front and/or back of the post and the difference in the minor and lajor axes should be easily measurable.

Finally, measure the outside diameter of the seat tube and see if you can detect any stampings under the paint, near the top or bottom of the seat tube. It would not be the first time that somebody has grabbed the wrong tube, put it in upside down or applied the wrong decal.

Grand Bois

It's very obviously pinched. No doubt about it. Just don't put a screwdrive partway down the tube and pry from side to side. I once punched through a 531 tube that way.

tsappenfield

The seat tube, at least at the top, is somewhat "ovalized" as I look down it. Lots of good advice here (as usual). Thanks to all who contributed their thoughts.
TSAPP