Seatpost Help!

[Big_Daddy_Sloth]

On this bike, no matter how much I tighten the seatpost (clincher?) bolt , the seat post still spins, slightly. By that, I mean it doesn't spin around like the wheel on WOF, but it will turn if I get all wiggly while riding. When I got it, the seat post was rusted in the seat tube and I had to struggle to get it out. I lubed it before putting it back in and now I have this problem.
A) Did I use too much lube?
B) Is the seatpost just a hair too small?

I don't know what to do.

Let me know if you need a better picture.
Thanks.

 

[B607]

I'd get rid of the lube. Get some laquer thinner and wipe down the tube and run a rag with thinner down the hole. Do you have a chrome seat post? They are notorious for moving around no matter how tight you make it. Gary

 

[mikesbikes36]

what he said ...n mayb try a popcan shim in there :mrgreen:

 

[Big_Daddy_Sloth]

Word. Thanks. The seatpost is chrome and the lube is force of habit.
I'll give it a cleaning and report back.

 

[gcrank1]

Those seatposts can vary in dia. a fair bit, too. I think the size is more nominal than exact. I have some that I can swap around to get a better fit in a seatube and some that have been clamped so tight they are out of round, so some brass hammer tune up was required. See if you can find somebody with a few more to try out for fit, its hard to cinch one too small tight enough. Ideally you should have to work it in rather than drop in.

 

[deorman]

Any chance you're trying to use a 13/16" post on a 7/8" tube?

 

[Big_Daddy_Sloth]

Any chance you're trying to use a 13/16" post on a 7/8" tube?

As soon as I get some calipers and am in the garage, I'll check. That was one of my thoughts as well. Thanks.

 

[gcrank1]

Sometimes you can slide sockets (as in socket set) in to get a good fit in a hole and measure that, just DONT drop one down in!!

 

[Saverio]

That's a good question about sizing seat posts.
Mine is stamped 25.4mm. I went to buy a 1" (forgot to measure the store bought pipe, but i'm assuming OD) pipe and it was WAY too big.
They only sell a few sizes, 1/4", 1/2, 3/4, and 1.
Am I interpreting this incorrectly?

I thought I'd head down to the hardware store and pick up some steel pipes and make mine own post, but can find the right size. My bike is a new Nirve, so I thought it'd use a more common size for aftermarket applications.

 

[gcrank1]

Nope,'pipe' is measured by the hole in the middle where the fluid flows; add the wall thickness and you end up with what you've got, WAY too big.

 

[Saverio]

Thanks for setting me straight. Learning as I go!

 

[Big_Daddy_Sloth]

Any chance you're trying to use a 13/16" post on a 7/8" tube?

Also, I want to add that I bought the bike this way. So maybe the person before me did it. And crud! I keep forgetting to borrow the digital calipers from work.

 

[gcrank1]

Many 'home repair centers' have the General tool brand, fairly inexpensive and mine are all good quality. They have a nice little dial caliper (not sure if its in thou/mm or fractions), but it should do for almost all your bike work.

 

[Big_Daddy_Sloth]

Ok, so I finally measured my seatpost tonight. I may need to re-check it, as this is what I got:
Seatpost 20.65mm
Seattube 19.53mm/19.94mm

It was getting dark and I was getting tired. I'll check again tomorrow. But do these sound somewhat right?

 

[jackdaw]

Yeah bud, a millimeter one way or the other will make a difference. One of the mysteries of the bike world, why seven or eight different seat post diameters? Why not say, three? Two mm apart and you could get to be able to tell the difference by eye. But no. When you buy seatposts they come measured to the tenth of a mm. Good luck!! You'll find one, or find a shim.

 

[gcrank1]

Got those numbers flipped?

 

[Big_Daddy_Sloth]

That was my first thought as well. I'm at work, so let me bust everything out and take pictures.

 

[Big_Daddy_Sloth]

Crud. I can't get the pictures to my email. But the new photos show -
Seatpost: 20.34*
Seattube: 20.28

* This is a guess-timate of the average. If I move the digital calipers around andthe seatpost and up and down the length, I get a huge range of numbers. :/

Any suggestions?

 

[gcrank1]

Seatpost is out of round (not unusual for the cranking that they take), but it cant fit into a seat tube of smaller dia. and still be too loose.......

 

[Big_Daddy_Sloth]

I think that's it, because as I posted previously, when I measured it, I got wildly different readings depending on where I put it.

Thanks.

Now what size do you think I need?