bikemig 

I picked up an early 70s Raleigh Gran Sport recently since obviously I don't have too many bike projects, . It was my size and I made the seller an offer that he unfortunately accepted. I blame gugie for this bike since he keeps telling me how great the gran sports are.

I think the bike may be a '72 with a Reynolds 531 main triangle but the bike has been modded. It has zeus drop outs and what looks to be a 6 digit serial number (I can't read the 6th digit) which according to cudak888 very helpful website likely makes this an early 70s: https://www.kurtkaminer.com/TH_raleigh_serials.html

The seatpost which I think is the original alloy straight post (very nicely made post with a made in england stamp) is a 27.2 but it is very, very tight. In fact I can't get a 27.0 or a 26.8 to fit in and a 26.6 is too loose. I'm fairly certain that this must be a 27.2 since that is pretty much the norm for Reynolds 531 double butted. In fact, mkeller234 has a thread on his 1973 Raleigh Gran Sport and it looks as if it had a 27.2 seatpost.

The ears on my bike are not bent or squashed. The seatpost that came with the bike should be the right size since I'm fairly certain it was original to the bike. I have no idea why it is so tight. Is the best solution to take a round file and clean up the inside until a 27.2 slots in? Anything else I should think about? I guess I should drill a round hole near the bottom of the slot. The close up of the slot makes it look worse than it is. There is a bit of rust there but no cracking. I have no idea why the right size seatpost doesn't fit properly.

T-Mar

This does not make sense. How can posts smaller than the removed post not fit? It sounds like the post may be mislabeled. Try measuring the current post on several unmarred sections. The cinch slot looks pretty parallel from bottom to top. Either it's the right size or possibly one size large (which would be essentially the same size as the inner diameter of the seat tube, so, depending on tolerances, there could be a light interference fit).

Reynolds 531 buttedseat tubes are typically single butted. They come in different gauges but the two most common for this era would employ either a 27.0mm or 27.2mm post for an imperial diameter seat tube.

Regardless, it is always advisable to clean up the inside of a seat tube. A round or half round file works well for removing burrs from the mouth and edges of the cinch slot. After that, I clean up the inside for a flex hone or, if it's damaged, a reamer. You can make do with some medium-fine grade sand paper. A stress hole at the bottom of the slot is a good precautionary measure, though if it hasn't cracked already, with a tight post, it likely isn't going to crack.

bikemig 

A 27.0 and a 26.8 won't fit in properly without forcing them in. They are what I use to check seatpost sizes on bikes that pass through my shop and I know they are properly marked.

I don't have a reamer or a hone but a file and sandpaper will make a difference. Thank you for the advice. I just think it's weird that what should be the original seatpost is so tight that it had a burr that I had to file when I removed it.

rustystrings61 

I have a '73 Raleigh Competition and a '73 Raleigh Gran Sport, both of which required a pass of a brake cylinder hone on an electric drill to get them to accept the correct 27.2 mm seat post. The correct size for these IS 27.2 mm, but much of the time there has been corrosion, etc. In both of my bikes' cases, they had been fitted with undersized posts that compounded the corrosion issue - and in both cases, after running the hone, a well-greased 27.2 post fit smoothly without drama.

This is the one I use, purchased on a side trip to autozone.

Hobbiano 

This is what I use: https://www.amazon.com/29mm-Flex-Hon...3168332&sr=8-4
I'm pretty sure this is the diameter I ordered. The next size smaller is 1". I keep it flushed with WD-40 while using it.

mkeller234

boy… it’s been a while since I looked. My gut says, yes, it is a 27.2 post. I’d have to pull it out and check. I think it might be a kalloy post??

Here is an old link I found. I forgot that mine had the wrong size post when I bought it, the ears were deformed. I see I installed a 27.2 Campy post to verify that as well.

steelbikeguy

just one thought.... maybe the seat tube is no longer round?
i.e. it might be a bit of an oval, preventing the right size post (that is round) from fitting.

I only mention this because one of my bikes had a bit of a problem with this. Reaming out the seat tube to make it round again also caused it to need a larger seat post. (this was done by a frame builder doing a bit of work on the frame)

Steve in Peoria

Mad Honk 

bikemig,
There are documented cases of Paramounts built with 531 tubing where the frame tubes for the seat post were installed upside down. At Schwinn they just put 26.8 seat posts in and kept the production moving. It is quite possible that you could have one of those rare birds. I would use a bit of sand paper on the inside of the tube to be sure it is smooth and try a 26.8 seat post. My wager is that it is one of those rare seat tube installs. Smiles, MH

bikemig 

I thinking this might be the issue. That would explain why the smaller size seatposts (27.0 and 26.8 don't fit). The smaller seatposts hit on two spots of the frame but they look like they would otherwise slide right in.

Charles Wahl

I agree with steelbikeguy that it's also likely the opening is out of round -- I hope you have a dial or (if you must) digital caliper. Every C&Ver needs a caliper for such situations. Also if, like many, many used bicycles, the removal of a seatpost scratches it up (zig-zag), then the seat tube opening needs, at the very least, to be filed or honed to remove whatever burrs are causing that. Chances are about 99% that this frame takes a 27.2 mm post. Posts vary somewhat in their quality and diameter -- I've found that some cheaper ones tend to be undersize -- but the one you removed may well be the original.

bikemig 

Yeah I think this is the problem as well. I'm curious why do you prefer a dial to a digital caliper? I have a vernier and a digital caliper,

Charles Wahl

I'm just an analog guy, for the most part. Seems to me that a digital (though I have no idea how they work) is converting analog movement to digital anyway, requires batteries, etc. Plus, dial caliper is C&V, and IMO looks better. Brown & Sharpe or Mitutoyo. I guess you could say that vernier is the most C&V, but it's sort of like the ur-derailleurs for me -- too primitive.

merziac

Also, IMO, this is where an oldschool hard, chrome steel post comes into play, tough rounded end, 1-2 sizes smaller than best guess, go after the ST with half round then apply axle grease and carefully tap the chromie in, stop quick if it even seems to start to seize. You can tap around on the post to correct a lot of wonkieness or get it back out, pretty easy with the right finesse.

oneclick 

I agree - had to do this recently:

https://www.bikeforums.net/21914819-post19.html

merziac

I thought we had this discussion recently, they must have your number to get two of them in such a short time span, or at all.

planetal

What was the final verdict? I have the same bike with the same problem. What size seatpost did you end up getting in ?

3alarmer 

.
...I think (but am not certain) that the issue was that the opening of the seat lug was out of round. The simplest, quickest, and most effective way to remedy that is to use a reamer.

The adjustable ones are relatively affordable online from e-bay or Amazon. But there are some tricks to adjusting and using one.

It's not rocket science, but it is important to carefully measure the reamer a couple of times after you adjust to whatever dimension you've chosen as your mark, and have the seatpost of choice close by, to check as you go. It can get snagged on the edges of the cut slot if you are not careful, and you need to remedy any crimping down of the ears/slot before you start.

52telecaster

I use a reamer as well. Just make sure the hole is reasonably round first. Hate to break out the side of a tube going for 27.2.

tiger1964 

My Gran Sport has been Campified at some point in the ancient past, but the seat post clearly says 27.2 on it.

Or its distant cousin, the automotive brake cylinder hone. I now use this on every bike, every time.

bikemig 

I had Jeff Bock, who is a very fine frame builder located in central Iowa , ream the seat tube out to 27.2.

bikemig 

This is an older thread that came back to life as old threads do from time to time. I ended up having Jeff Bock, who is a very fine frame builder and local to me, ream the seat tube out to 27.2. I'd wanted a 70s era Raleigh Gran Sports for a while. I used to go and hang out at a local bike shop in the 70s and I thought the white and blue Raleighs were beautiful. I was a kid and I sure as heck couldn't afford one. Now, if you can find one, they're all on deep sale; go figure,

The bike came to me as a bit of Frankenbike so I stayed with that idea to turn it into an all around rider, good for long rides and light gravel roads. I'm running a deore triple as a compact double with 50/36 rings and a 13-30 6 speed suntour new winner reewheel. I found a set of weinman 610 brakes which is what the bike would have come with originally. I had to ream out the the calipers a bit to get the pads to reach to 700c wheels. The wheels are Mavic MA 40 rims laced to suntour gpx low flange hubs and the tires are 700 x 35c Marathon racers. The stem and handlebars are new. The saddle came on the bike and it's fine. The only thing original at this point on the bike is the headset and possibly the saddle. This is just a really nice riding bike and the build came out nicely as well.

bulgie 

I liked my verniers for years until my eyesight dgraded to where I couldn't read it reliably anymore. Then I hit on the killer app, close-up pic with the phone, then pinch to zoom.
Not exactly fast, but I can read it to a thousandth of an inch.

I have good Mitutoyo digital calipers, real ones not fakes (watch out for those!) but I only pull them out for important stuff, trying to keep the wear'n'tear to a minimum. I also have cheap digitals, which are faster than the vernier but actually less precise, plus pretty often when I go to use them, the battery is dead. They use battery all the time even when switched off, who thought up that brilliant idea? My Mitutoyo probably goes a year or more on a battery, and it doesn't even have auto-shut-off. Sometimes I find it with yesterday's last measurement still displayed. A nice feature sometimes, when you didn't write the number down, and since batteries still last a crazy long time, I wouldn't choose an auto-off even if they offered it. It's like magic how little battery they use.