Todd, et al.
Seat tube lugs are frequently out of round due to warpage caused by excessive heat used to braze on the seatstays and create a filet between the lug and the top of the stays. I've seen this to a degree in just about every bike I own from an Illkeson built 1974 Raleigh Team Pro to lowly French hacks.
Sometimes the opening is round and the correct size at the top but the tube is bulged inward further down.
Many makers ran a reamer though the seat tube to clean up any excessive paint from overspray before assembly. If you look carefully inside the seat tube on many frames you can see the out of roundness where the reamer hasn't completely removed the paint.
I think that at times, manufacturers kept an assortment of seatpost sizes in their assembly areas and installed what ever fit. I recently picked up a full Campy equipped early 70s Gitane Super Corsa. This bike should have had a 26.4 mm seat post but had a rare Campy 25.8 mm post. It appeared to have come from the factory that way.
The seat tube and lug were very out of round. I rounded out the tube using a series of old 1/2" drive sockets with the appropriate OD and resized it to 26.4 mm with an adjustable reamer.
I mount a socket on a length of threaded rod with nuts and washers above and below so that I can easily remove it from the seat tube. I gently tap the socket into tube, take it out and switch to the next larger size socket and repeat the operation.
After it's fairly round I run a large adjustable reamer down the tube to resize it and then I finish the job with an automotive brake cylinder hone to smooth out the tube and remove any burrs.
I use the hone to clean up the seat tube and steerer on every frame that I build up or work on. It makes for easier assembly.
Hint, If you are working on an assembled bike, turn it upside-down or on it's side so that dirt and crud don't fall into you BB bearings. I avoid putting a rag or paper towel down the seat tube because it's difficult to remove with the BB installed and it's likely to absorb moisture if left in and cause rusting.
One other consideration, many frames have had undersized seatposts installed and the seat lug has been squeezed out of round. I carefully open up the bolt "ears" on the seat lug so that the slot between them is straight up and down. Do this with a seatpost in the tube so when you are spreading the ears you don't bend the seat tubing inward at the split.
Chas. Colerich Oakland, CA
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