27.4 too tight and 27.2 too slack

d8mok · Jul 19, 2019

In preparation for last few bits arriving I started to build my Lightning slightly.

It came with a 27.4 post which looked fairly standard and fitted well but a little tight but nothing too bad.

I wanted a Thomson so tried my 27.2 I had and it was way too slack. So I’ve purchased a new 27.4 and it’s way too tight and will only go in 2-3 inches max.

Any ideas?

mk one · Jul 19, 2019

Seat posts can be different diameter than stated on post, quite common from on manufacturer to another and even with the same manufacturer. This is not taking into account any deformaties in the seat tube itself.

d8mok · Jul 19, 2019

Best course of action?

As 27.2 is no good and neither is 27.4. Not keen on buying any other posts as it was fairly expensive to keep trying different ones.

Maybe ream the frame to 27.4 to make sure it’s right ?

mk one · Jul 19, 2019

There is a post on this thread about the diameters of the '97 and '98 models; viewtopic.php?f=1&t=60030

It sounds like yours is a 27.4 and the post is slightly larger. Personally i wouldnt ream the frame for the sake of a post. I have a few posts so can usually find one that fits, i can see how you wouldnt want to keep buying them though.

You could always take it to a LBS and get the to double check the size, and then try to sell the post to fund another. Sorry not much help.

d8mok · Jul 19, 2019

Re:

Thanks for reply. Yeh I’ve already seen the post you linked. 27.2 is definitely too small as I’ve tried several. The 27.4 size seems rare though and not many manufacturers make them. Won’t be buying another post as it wasn’t cheap and can’t be sent back now as it’s marked a tiny bit

LongboardSi · Jul 19, 2019

couple of options, but can see why you might not want to go with either...

- cheap seatposts have fairly thick walls - you might be better off machining down a thick-walled seatpost very slightly...

or

- you can get adjustable shims (really - wasn't sure how this would work when I first heard about them) which are basically two tapered parts that slide inside each other. I have one on a USE post and means it'll fit a range of frames easily. Doesn't look super slick, but actually works really well, and is easier to get nicely secure than the proper USE shim I have on my KHS.

there's one here, but it's not as reassuringly deep as a USE one. https://www.amazon.co.uk/Raleigh-Seatpo ... FYXTW5EA9X

d8mok · Jul 19, 2019

Re:

To be honest I don’t want a cheap seat post as it’s a fairly nice build. I’ve still got the standard one if needed anyway but it’s not in fitting with the build spec wise. The thomson post was about £70 and doubt I’d see much back for it in its wierd size.

I’ll have a think but I think I’ll either be reaming the frame , machining the post down slightly or might just bin off the project as I was only doing it for a little project not because I need another bike

hamster · Jul 19, 2019

I'd run a reamer through the frame. The issue is a tolerance build up. Have you tried greasing the post? My Litespeed will take a 27.2 but needs a smear of grease to get it to fit without a struggle.

d8mok · Jul 19, 2019

Re:

Yeh tried grease but it doesn’t do anything. If I’d not got a 27.2 I’d of said it was too big.

Duxuk · Jul 19, 2019

Re:

Are you sure your seat tube is clinically clean and corrosion free?

27.4 too tight and 27.2 too slack

d8mok

mk one

d8mok

mk one

d8mok

LongboardSi

Senior Retro Guru

d8mok

hamster

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d8mok

Duxuk

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