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Seat post bolt for early 50s rebuild

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Seat post bolt for early 50s rebuild

Old 06-21-20, 08:36 AM
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Andiroo99
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Seat post bolt for early 50s rebuild

Hi

Rebuilding an early 50s classic british lightweight. Balancing mix of ridability with authenticity. Usually I would go for campag bolt but not sure its ideal for this fitting. Any suggestions?

Regards

arb



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Old 06-21-20, 08:44 AM
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Oh, I want to see this when it’s finished!
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Old 06-21-20, 08:52 AM
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Charles Wahl
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Inside diameter and the nominal span across the lugs might be useful info to have.

Here's the seat post bolt from a 1950 R.O. Harrison frame:



The bolt is 35 mm (1-3/8") long below the head, with a rounded head (no flats or other means of holding it) that's keyed as you can see. The unthreaded part of the shaft is 7.8 mm (0.307", not quite 5/16") in diameter, and the nut is a "pierced acorn" type. I suspect that the washer may be a replacement -- I at first thought it was brass, but I think that's just some sort of yellowish chromate corrosion coating.

The one on a 1950s R.J.R. (early Bob Jackson) is virtually identical, with a thinner washer, which also might be a replacement.

Somewhere or other around here there's the bolt for a late 1950s F.W. Evans too. Seatpost clamp lugs on all 3 bikes look pretty much the same, but they're the formed/bent type, not brazed-on tubes like you have (which are similar to later (80s) frames I have, such as a Serotta, a TSD Guerciotti, a Motobécane Team Champion and Specialized Expedition.

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Old 06-21-20, 08:55 AM
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Will get out the calipers later today.
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Old 06-21-20, 02:14 PM
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Hi

The outside span is 0.82" (2.08cm) and the inside diameter of the hole is 0.31" (0.78cm).

Any further thoughts on vintage or more modern (but suitable) options?

Arb





Originally Posted by Charles Wahl View Post
Inside diameter and the nominal span across the lugs might be useful info to have.

Here's the seat post bolt from a 1950 R.O. Harrison frame:



The bolt is 35 mm (1-3/8") long below the head, with a rounded head (no flats or other means of holding it) that's keyed as you can see. The unthreaded part of the shaft is 7.8 mm (0.307", not quite 5/16") in diameter, and the nut is a "pierced acorn" type. I suspect that the washer may be a replacement -- I at first thought it was brass, but I think that's just some sort of yellowish chromate corrosion coating.

The one on a 1950s R.J.R. (early Bob Jackson) is virtually identical, with a thinner washer, which also might be a replacement.

Somewhere or other around here there's the bolt for a late 1950s F.W. Evans too. Seatpost clamp lugs on all 3 bikes look pretty much the same, but they're the formed/bent type, not brazed-on tubes like you have (which are similar to later (80s) frames I have, such as a Serotta, a TSD Guerciotti, a Motobécane Team Champion and Specialized Expedition.
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Old 06-21-20, 02:58 PM
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Bolts like that are readily available for a couple of quarters. A dozen for €4.90, to be precise:

https://www.internet-bikes.com/30857...-per-12-stuks/
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Old 06-21-20, 03:41 PM
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Charles Wahl
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A pretty-much-standard Campagnolo seat post binder bolt from the 80s is 8 mm diameter x about 20 mm nominal length (screwed in all the way, I think) -- and these things are available (both vintage and new) on eBay, by many manufacturers, either bike marques or Sugino. Armed with the knowledge you now have, press on. The 80s type typically have either a knurled end by the "fixed" side of the bolt (for a non-keyed hole) or a key like the bolt shown above. But provided the diameter and length are reasonably correct, a key can be filed into one side (carefully, with file or Dremel tool), and doesn't prevent use of the knurled type either. The later models have no nut, but internal threads and are tightened with a hex key.
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Old 06-22-20, 04:13 AM
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A seat binder bolt like Charles Wahl shows depends on the strength of the steel key and the slot on the frame. I've seen too many of those fail due to the torque applied on the nut, trying to secure the seat post. Turns the bolt, strips the key, then the bolt just spins and you have to grab the head with vice grip pliers. Then folks replace the whole thing with a plain bolt so they can hold the bolt head. Then lock washers and star washers. UGH! I'll only use binder bolts that have a hex socket in the head, using two tools to apply torque on each side of the binder. And I always use two tools (ex: two 5mm hex keys). Even if the binder bolt had a key on the head too (ex: Sugino seat bolts) I use two keys. Why damage things when you don't have too? Two keyed bolts are a design that lasts.

So, I recommend finding or making a bold with a "socket head", either a dual headed binder bolt or a stainless socket head bolt with a nut. It will hold the post without buggering the frame. Maybe you can find a neat 1950's Carlton specialty nut. They're out there.
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