How tight should a seat post be to fit frame?

[Zippy]

The time has come for me to fit the new seat post (having burned the old one out with caustic) but although I have the right size (according to tthe lbs) it is going in about four inches and then becomes too tight to turn in the frame.

This is without the saddle fitted though, just inserting the stem by hand.

How tight a fit should it be? I don't want to end up at square one!

 

[fossyant]

There could be some crap down there..... you might need some sand paper to get rid of it - tape the sand paper to a smaller gauge tube (wooden dowel). I'd remove the BB so you can clean out.

Are you fitting it with plenty of grease/copper slip ? I assume this is a steel frame.. ?

I'd fit the saddle as well as you have zero leverage without.

 

[Zippy]

OK, I think I answered the above myself as some folks whip their saddles out oft he frame when nipping into shops and such, so I should be able to just slide the saddle stem into the frame with the QR doing the lock in - right?

Well I have to heave and twist the stem I was sold by the technician at my lbs and I think I now understand why. The technician tried a narrower stem in the frame which showed about a 1mm of play with the QR off the frame and said I needed a slightly bigger stem to take out the play.

Now a week later for it to be ordered and it fits the open frame collar, but won't go past say 2 inches down the tube and that is because he fit the stem to the open collar of the frame and not the actual tube diameter .

Surely a bike technician should have known that?

Trouble is now, because I used the seat stem to ream out any remaining aluminium oxide (from chemically removing the old one - see famous thread) before realising it was the wrong size completely it is now no way resaleable! OK it was their fault for ordering the wrong part, but my fault for trying to ream the dirt out of my frame with it so I doubt they'll see eye to ey for a reufnd!

I don't suppose anyone here wants to buy a brand new but cosmetically scrawped seat post? Silver coloured PUSH seatpost, Layback profile, 6061 Aluminium, 400mm length, single bolt adjustment, 26.8 diam.

Cost me £21.99 - on sale here at £10.00, post free. PayPal accepted and the mods know where I live so buy in confidence!

 

[gbb]

I dont know why, but my seatpost is remarkably difficult to get into my old Raleigh.
In line with Fossys suggestion, i use a metal rod, cut a slot 1 inch long into one end and feed in some emery tape, wrap the emery tape round the rod, then put the rod in a drill. You can work deep into the seat tube that way.
That said, mines still tight even after cleaning out the seat tube.

There's no dings in the seat tube are there, this would make the seatpost tight.

 

[hubgearfreak]

if it's gone in four or five inches, which it clearly has, then it's gone in far enough to be properly fixed to the frame. so, just measure how much seatpin you need showing, add 4 inches and chop off the rest. no need to buy another, and it'll be the devils own job for a thief.
just don't forget to take it out and coppergrease it at least annually, although i'm perhaps preaching to the converted with that bit of advice

 

[Zippy]

Thanks hubgearfreak. You got it right about the coppergrease after all that!
Good point about the 4-5 inches being a safe fitting. I was gonna hafta cut some off the length anyway as the seat post is about as long as the downtube! Short legged guy that I am!

Thinking outta the box - thanks!

I have this from Bikers Forum (or is that swearing on here?):

Just to be safe, keep three inches of insertion or to about an inch and a half below the bottom of the top tube, which ever is longer. You can hack off the rest.

If that is the case, I am well above that and have some to hack off anyways.

Its gonna be a good ride when its done :-)

 

[hubgearfreak]

keep three inches of insertion

fnarr, fnarr. to found out, i'd go to my LBS and see where the min insertion mark is, on the posts that are marked

 

[Zippy]

It was the techy at my LBS who measured my seat post needs from an open collared downtube (not taking into account the smaller diameter when QR closes the tube mouth down) - I'd've done better at Halfords! Sure I didn't think about it either, but he's the technician! Sheesh! Got better advice from CC - but of course, where else!

 

[hubgearfreak]

no, i mean just ask to look at the seatposts in stock, not ask his advice

 

[Zippy]

I know. I think the lbs were just after getting me to buy a new bike and were even quite dismissive when I triumphantly waved my frame in their when I had managed to burn out the stuck one! Oh well done <slow hand clap> (give the man a prize; one more bike we don't get to sell).

The problem in Cornwall is if you don't like the lbs in your town, the next one is in the next town so you get all sorts of tech' abilities. We slag off Halfords a bit, but down here at least their trained!

My next lbs is a forty mile round trip.

The min line (before I scrawped it off trying to insert it) was three inches so I guess my five would be adequate . Now where's me hacksaw - oh, must remember to put the wheel on first!

 

[02GF74]

5 inches is more than plenty.

to cut the tube neatly, you can use a pipe cutter - clamp thing with a thin hardeed steel wheel - be ok to use on alloy. (I have used them to cut steel pipe but it quickly wears the wheel out )

otherwise fit a jubille clip to use as a guide for your hacksaw.

.... but in the end, it can't be seen so doesn't really matter if neat or not.

 

[e-rider]

A few points to note on this one:

If they sold you a 26.8 and you are saying it's slightly too big then you are suggesting that you really need a 26.6 - right?

26.8 is a very common size

26.6 is a very rare size!

Try this: get a wooden tube/dowel or similar and attach (using duct tape) one of those green abrasive cloths you use in the kitchen (sometimes attached to a yellow sponge)

Give the inside of the seat tube a real good going at with this. It should not be so abbrasive that you atculally remove the aluminium but it will give it a real good clean out.

I had some trouble after having a frame resprayed once - it looked pretty clean inside the seat tube and I'd had the sand paper in there but the post was very very tight. I tried this trick and within 5 minutes my post was slipping in perfectly with minimal effort!

 

[tyred]

I have the opposite problem on an old Peugeot frame where the seat pin appears to fit perfectly, yet over the course of a week or so of regular riding, it will creep down by about half an inch, no matter how tight I tighten the clamp. It is a steel frame and steel pin but a smaller size than most bikes.

 

[Crankarm]

+1 the plumber's pipe cutter. Essential really to cut it properly and cleanly.

Wrt the seat post tube. Buy one of those metal brushes on a long metal stick about 12" which you can put into a drill - MachineMart or Wickes do them. Put that down the seat tube to clean it out using a drill to turn it. Turn the frame upside down so all the crap falls out. Grease the internal diameter of the seat tube before you insert the seat post. I've found it helps not to get grease on the surfaces where the clamp directly sits otherwise the seat can slip down over time which is annoying.

The seat post should then fit snugly in the seat tube. It should not be loose or rattle. If so, it's diameter is too small. Wasn't the diameter stamped on your old seat post or could you not measure it with calipers?