I just bought a Simplex post for my Grubb frame, and it goes in very tightly, and then, after a few inches, I can't push it down any farther. I'm wondering what I'm hitting.
The person I bought the frame from told me that the seatpost diameter is 26.4, so I measured it as well as I could, and it seemed to be about accurate. I then bought a 26.4 Simplex,
and like I say, even though I greased the inside of the seat tube and the post, it goes in very tightly.., and then stops about 1/2" short of where I need it to be.
Why would a post stop in the seattube? Do I need a 26.2 seat post?
The flanges for the binder bolt are angled slightly away from eachother with the post in.
I think the tubing is straight guage, either A&P or 531.
Mid-1950's frame.

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i would take the frame and post to a bike shop and ask them to measure the seat tube inside diameter with their tool.

if i needed a 26.2 seatpost instead, i might think about filing 0.1mm from it. (0.1mm shaved all the way around equals 0.2mm in diameter.)

a lot of new posts are also way too long for vintage bikes, so you could cut it to size and try it in the frame again. you only need about an inch of post below the seat lug.

also, old bike frames develop a lot of scale inside the tubes that you may try to file or sand away.

Cut 1/2 inch off.

what they say. Seems like the cut is the way to go.

How far in is the seatpost when it binds? When I worked in bicycle shops the rule of thumb was 2 inches inserted BELOW the top tube. Some seatubes have a fair bit above the top tube and if the seastpost isn't inserted to a couple of inches BELOW the top tube the lever effect of the seatpost and rider can snap off the seat tube. I seen a number of frames where that's happened.

Is your post hitting a seat tube bottle mount?

Is the interior of the saet tuber rusted or is the seat tube dented?

I bought a bike that had this problem but it was in the steerer tube. The stem would go down but not as far as i wanted. Took out the stem, shone a bright light into the steerer and found that someone had cut off a stem and hammered the section left down into the bottom of the steerer. Fortunately i was able to bore out that piece.

Cheers

Ream the seattube. A good shop should be able to do this.

There is a small dent on the seat tube, about 2.5" from the top. That must be what I'm hitting. There does seem to be a fair amount of oxidation on the inside of the frame, at least I see an orange hue when I check with a flashlight.
I would not know how to go about filing, sanding or reaming the inside of a seat tube, but I am taking it to one of Boston's best frame-builder's, Peter Mooney, and he'll know what to do.
If fate has it that this seat tube is 26.2 (Sheldon Brown said some straight guage 531 was 26.2 i.d.), then I'll get one that size and sell the Simplex.
I really didn't think the small dent would affect the inside of the tube, but I expected a lot of surprises when I began this project.
Miele, this frame has no bottle mounts.
Thanks for the suggestions.

Update: I got in there and delicately worked a taper file and the 26.4 post slid in all the way to the optimum point! Thanks, people.

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