Hi,

I was installing a new seatpost and ran into some difficulty. I am hoping someone here can share there experience.

Here's the situation:

I installed a new seatpost but it wasn't easy. The old seatpost is 27.2mm (or so it says on the seatpost) and the new seatpost is also 27.2mm (at least that's what is says on the package and on the post). The old one came out very easily while the new one wouldn't go in past 2". After wrestling with it for a few minutes (yes, I did put a thin layer of grease on it) I decided to be more generous with the grease, put some big GOBS on the post and, with some force, it finally slid into the tube.

Prior to installing I checked the seat tube to make sure it was free of obstructions and checked both seatposts with my vernier calipers. They both measured in at 27.2mm and the seat tube was clear (except for the expected grit, sand, dirt, whatever) of any obstructions.

So why was it so hard to get the new post installed while it was so easy to remove the old one? By the way, both seatposts are alloy and the frame is chromoly steel. There is a seatpost clamp with a shim. I actually tried installing the post without the shim, but that wasn't ideal (too much space).

Thanks in advance.

Every manufactured product has a tolerance. It could be that your frame is bored toward the minimum size, and the post is at the large end. Both parts are within tolerance, yet the pair are unusually tight together.

There are other possibilities, but your post implies that all is good now, so deeper analysis isn't necessary.

Thanks, but just wondering (yeah, I'm a curious little guy), what would the other possibilities be, for example?

A burr someplace, the new post being slightly oval, just for starters, but the most likely issue is the simplest one -- tolerance. Namely the new post is slightly larger than the old one.

Thanks. That makes sense. Well, at least I know a thief will not have an easy time stealing my seatpost.

Suggest that the OP periodically remove, clean and relube the post. Even post of the "correct fit" can and will seize in place if left in place too long. Andy.

i would be interested in how far the old seatpost was inserted into the seattube. if it was about two inches, i would think i was well on my way to understanding the nature of the mystery.

[MENTION=204]andy[/MENTION]: Yes, that's sound advice, though I am not sure I'm able to easily remove the seatpost, now. Although, now I am wondering if I should try a different seatpost, at this juncture, just for the sake of easy removal in the future.
[MENTION=211350]hueyhoolihan[/MENTION]: Looking at all the scratches on the old post, I'd say it went into the seat tube at least 5".

Speaking of which - when you decide to remove the post, there is a name you should be familiar with: PB Blaster. It's a spray-on super penetrating hydrocarbon that can help loosen up such a dilemna.

[MENTION=140740]Panthers007[/MENTION]: Hey, thanks! I'll remember that.

When fitting a seatpost you should put some grease inside the seat tube, so it'll be pushed down.

If you only put grease on the post, the excess just gathers at the top of the seat tube.

From what material is your frame build and how old is it? Metal tiredness, can be the matter here.

The only thing that gets tired on my bike is the engine Perhaps Swen means that the binder ears can distort with over tightening, too small a post having been used, poor design, heat induced warping during the building and or poor after construction finishing.

I hope Swen is not trying to imply metal gets soft with time. We all know that, if anything, it's the opposite that happens. Andy.

There are minor production variations .. not all 27.2 mm seat-posts are made to a 27.200mm, tolerance.

ie, measured to the nearest thousandth of a MM..

Probably a mistranslation of metal fatigue into "tired" metal by a non-native speaker. Metal fatigue is caused by work hardening.

Yes, I wondered about this. But my reply is also for many others too. Andy.

You usually need to take something like a long "rat tail" file and just touch up the inside of the seat post to get rid of the slight amount of rust, or dirt that likely accumulated at the bottom of wher the old seat post sat for years. And like most manufacturers, tollerances can be different. Even a micrometer between two tubes that are listed as the same diameter, plus the possible dirt and surface rust inside the seat tube, will make for a very tight fit. It doesn't atke much friction in a tight fitting tube to bring things to a halt. After a bit of a "burnishing" with the rat tail file, a bit of lubricating spay down into the seat tube will help any adjustments or removal of teh seat in teh future.

Yes in Dutch it is metaal moeheid, so certainly directly translated.

Ball burnisher (looks like a grape cluster), or perhaps a brake cylinder hone [Car Drum brake era tools] will smooth out the seat tube bore ..

Still readily available for less than $10: 1-1/8" Brake Cylinder Hone

I have one and it works quite well on steel frames (though be careful around the seat clamp slot).