surfjimc

I picked up an 84 Specialized Expedition a while back and have been slowly getting parts off of ebay to rebuild it as a total upgrade.
The seatpost was a mess, but it looked like it said 26.8, so when I found a good deal on a 26.8 Thompson, I picked it up, but it doesn't fit. Just a hair too large. Does anyone know the seatpost size for that bike?

ernok1923

who much of a difference is it? while i don't officialy recommend anyone doing this: i had some success sanding the slightest bit of metal off one of my seatposts. actually, even 'slightest bit' sounds too expansive. it was so little that it won't effect structural integrity. you could think about doing that if it is close.

best way i have found to measure for a seatpost is with some digital calipers. very cheap (about $16) and have been very valuable in helping my build up my bike last year. was able to perfectly check bottom bracket width, seatpost size, tube diameter for front derailleur, etc.

rodar y rodar

Precision calipers (whether dial, digital. or vernier) are really handy for bicyclists because of the huge variety of "standards". But if you use them for the end of a piece of tubing, especially if it`s slotted tubing and has been clamped, you need to take your reading with a grain of salt. Probably better to measure the old seatpost or have someone with calipers measure it, provided it fits well.

HardyWeinberg

I'd guess 26.6 but yeah calipers tell the truth

rhm

You might want to wrap a broomstick in sandpaper and clean out the seat tube; you probably have a burr of metal, or maybe a rust spot or something in there. Whatever messed up your old seatpost will mess up your new one just as bad, and you should get rid of it. This may involve letting metal filings fall down into the BB, so depending on what that is, you may have to overhaul it afterwards. You can pretty well go to town with the sandpaper; working by hand, it would take years to remove enough material to hurt the frame or even change the seatpost size.

matchy99

Take the frame to a bike shop and they will use a flex hone to ream out the seat tube just a tiny bit to get your Thompson post to fit. This should cost you $20 at any decent shop.

TheBrick

+1 Also a bike shop should have a seat post sizing gauge. It's alot like a ring sizing gauge.

Beelzebutt

i have an 80's expedition and i just looked at my seatpost to make sure and its deffinately 26.8

id clean it before i ream it.. get a flashlight down there and look.. also have a look at the binder bolt area and make sure it hasnt been over squezed on a smaller seatpost at some point in its lifetime. if thats the case you can slightly spread it with a flathead screwdriver. look at the open slot in the back of your seat post clamp area.. if its almost squezed together without the bolt even in thats likely your problem.

Metzinger

Um, or you could invert the bike when doing this.