Brompton Seat Post sleeve

[Fastpedaller]

I've seen a Youtube clip showing how to replace the bush in the top of the seat tube if it wears too much and won't clamp the seat tube correctly. All looks reasonable.. 1) remove old one 2) clean everything 3) dry - fit new bush and with a (slightly undersize) mandrill, check it is ok. 4) remove mandrill, put glue on inside of seat tube and insert sleeve and mandrill.(my simplified wording) 5) clamp and allow to dry. 6 ) ream with huge reamer inserted into lower part of frame ie pointing upwards (yes it's a huge reamer!.

Here's my thought..... I'm sure the cost of the huge reamer is equally huge. What about......a) Having removed old and cleaned, 2)dry fit new and insert seatpin to see if it fits (don't push super-hard and get it stuck! 3)If it's too tight, remove sleeve and with some fine sandpaper remove a few thou' from the outside of the sleeve (and the 'lip' on the sleeve) 4) repeat as necessary 5) Once the sliding fit is achieved and the clamp seems to work correctly, remove pin and sleeve. 6) add glue and put sleeve into position. Insert seat pin, clamp it with qr as normal and leave to dry. All should be good again.
What do others think (who can't afford/don't want to buy a reamer?
p.s. mine doesn't need doing, but I like to think ahead

 

[LittleWheelsandBig]

It isn’t a matter of a few thou.

The reason for reaming the sleeve is make the sleeve’s internal surface round when the outside of the sleeve is inserted into a non-round seat tube (distorted by brazing). Some seat tubes are close to round and the reaming is fairly even all round. My Brompton was not.

If the inside of the sleeve is not round, either the seat-post doesn't slide down when the QR is opened or it slides down while you are riding.

 

[Fastpedaller]

It isn’t a matter of a few thou.

The reason for reaming the sleeve is make the sleeve’s internal surface round when the outside of the sleeve is inserted into a non-round seat tube (distorted by brazing). Some seat tubes are close to round and the reaming is fairly even all round. My Brompton was not.

If the inside of the sleeve is not round, either the seat-post doesn't slide down when the QR is opened or it slides down while you are riding.

Yes, I understand the procedure using the reamer is the best way. To be clear, I'm not suggesting removing any material from the inside of the sleeve, just its outside. Is the inside of the sleeve nice and round, or does it always need reaming?

 

[berlinonaut]

While you can try to get around following the proper process and the proper tools it is a bit of an useless approach in my eyes as typicaly it will lead to unreliable and suboptimal results. A slipping seat post is one of the most annoying things that can happen on the Brompton as it is disturbing every single ride massively and reliably. The seat post sleeve is designed as a consumable that has to be replaced every couple of years. In most cases about like every five years or so, depending on how often you fold the bike and how clean the riding environment is.
While the sleeve itself is cheap it's proper function is a core part of a good riding experience. Even many dealers struggle with executing the process properly, even if they have the reamer from Brompton. If it is done improperly you have to do it again and it may even result in nasty accidents on the road (I personally know of one such case).
In former years Brompton sold "prereamed" sleeves to avoid the necessity of the reamer. It turned out that this led to unsufficient results. I can testify that, having used those in the past. If you try to take shortcuts in the process this will typically at best lead to having to replace the sleeve earlier next time, in most cases it leads to a slipping seat post, so the whole operation was useless.
So just bite the bullet and either let a qualified workshop do the task (which should be affordable every couple of years) or buy the proper tool (which is expensive and probably not worth it for a private person). I did use the prereamed sleeves, tried to work around the reamer in various ways and used the proper way using the reamer - of the three clearly and solitarily the use of the reamer is leading to the desired result. Plus: Nothing beats experience - an inexperienced fool with a tool is still a fool and a youtube video is probably not enough to deal with all the tiny issues that are relevant and influence the outcome. Greed is not a good advice here.

Here's the official document by Brompton about the job:

https://trade.brompton.com/Uploads/QPart/QPart-Datasheets/ds-stslv.pdf

Even following this you still may run into issues.

 

[berlinonaut]

Yes, I understand the procedure using the reamer is the best way. To be clear, I'm not suggesting removing any material from the inside of the sleeve, just its outside. Is the inside of the sleeve nice and round, or does it always need reaming?

Seems you don't understand the topic yet. When the bike is new both, seat tube and seat post are perfectly round. Over time the sleeve wears through the folding process and becomes slimmer. You can and have to compensate this by adjusting the bolt of the seat post clamp, but only slightly. After some time you have to exchange the sleeve. Depending from how early or how late you do that and how much you have tightened the bolt one or both of seat tube or seat post may no longer be perfectly round but slightly oval. To compensate for that the new sleeve is too thick to fit the seat post. But it will fit the now more or less ovalish seat tube and with the reamer you will be able to cut a perfectly round fitting for the seat post. To achieve this you obviously have to ream the inside of the fitted sleeve and in no way remove material from the outside - this would be of no use at all and you'd end up with a non fitting sleeve AND a slipping seat post.
If you exchange the sleeve late you may have to bend the seat tube back in shape at the clamping area. If you exchange the sleeve too late you may have damaged the frame already. Also, one should always check wether the seat post is still round. If it is not round enough any more (again a typical result of changing the sleeve too late and thus having overtightened the clamp blot to compensate for that) you need to exchange the seat post.
Really: Let a workshop do the task. It is not overly expensive and trying to do it yourself w/o knowing what you are doing may not only lead to insufficient results and having to buy twice but to damaging your bike or even your health. Greed and overestimating own abilities while underestimating complexity are not a good advice here.

 

[Fastpedaller]

After reading the official brompton document linked above I'm a bit puzzled as it doesn't mention the reamer. It even suggests filing some material from the sleeve. Maybe my method would be good? One thing I've learnt over the years is that i'd rather mess it up myself than have the added expense or agro of someone else messing it up! Anyway a moot point, as mine doesn't need replacing (yet)

 

[berlinonaut]

After reading the official brompton document linked above I'm a bit puzzled as it doesn't mention the reamer.

As this document dates from 2012 and was intended for the general public it probably refers to the prereamed sleeves that are no longer available.

Maybe my method would be good?

As said before: No. Not at all.

One thing I've learnt over the years is that i'd rather mess it up myself than have the added expense or agro of someone else messing it up!

Feel free. Everbody has to make his own mistakes to be able to learn. I do own the Brompton reamer in the meantime and I do it for a reason...

 

[Fastpedaller]

What price is a reamer? I can't find one online except for an adjustable one on Amazon which would do the job if it was longer (surprised at less than £30), so may be affordable

 

[berlinonaut]

What price is a reamer?

180€ for the complete kit. https://www.vlerickfietsen.be/nl/brompton-montage-toolkit-voor-glijbus-van-hoofdframe

You may be able to achieve good results with a generic adjustable reamer from fleabay (a lot of them are russian or chinese) but I've no experience with them. The proper kit is expensive (and probably not worth buying for a private person if you don't own a lot of Bromptons) but clearly designed for the job and delivers perfect results when used properly.

 

[berlinonaut]

Here's btw. the Brompton manual for use WITH the reamer: https://www.vlerickfietsen.be/download-asset/158a1670-1731-11ea-9eb5-005056985c04

 

[Fastpedaller]

Thanks for that - much appreciated. I guess if it's affordable to get an adjustable reamer of sufficient length it could be done, some 'guide bushes' could be found amongst the useful bits in the garage to ensure the reamer is kept central to the seat tube at the lower end. The only other 'problem' is not having the mandrell, the use of which ensures the sleeve has adhered properly to the seat tube. Cheaper ways of doing things are rarely easier!

 

[12boy]

If you don't want to spend the money there is a cheap and kludgy way to fix this.... get a seat clamp of the correct size and tighten this on the seat post at the right place so the seat post can't slide down. You will have loosen and retighten every time you fold the bike up all the way but it will work, if the current clamp doesn't grip enough to prevent the downward slide but does grip well enough to prevent the saddle rotating. Sooner or later you will find this annoying enough to have it done correctly.

 

[rogerzilla]

I have the reaming kit now (it was £40 unused), but I had perfect results with a pre-reamed sleeve in the past. I must have got lucky. I broke out the old sleeve and the frame went for respray. Then I glued the pre-reamed sleeve in with Unibond Extreme Power Glue, clamped in the seatpost, and left it overnight. It has never slipped, it drops freely when unclamped, and the seat clamp opens and closes under fingertip pressure. It is the factory titanium post, which will be less slippy than chromed steel.

 

[berlinonaut]

I had perfect results with a pre-reamed sleeve in the past. I must have got lucky. I broke out the old sleeve and the frame went for respray. Then I glued the pre-reamed sleeve in with Unibond Extreme Power Glue, clamped in the seatpost, and left it overnight. It has never slipped, it drops freely when unclamped, and the seat clamp opens and closes under fingertip pressure. It is the factory titanium post, which will be less slippy than chromed steel.

The Ti-post may be one factor, the other may be the condition of the saddle tube and the seat post. If they are round and have not been overtightened pre reamed may work - that's probably why Brompton offered it in the first place: To make in time maintenance less stressful, cheap and easy.
On the other hand: If you are late to the party your seat post may even wobble in the frame with the clamp open. A pretty sure sign that something is seriously wrong.

 

[LittleWheelsandBig]

It is not unusual for unused Brompton seat tubes to be not round before a sleeve is fitted, let alone in a well-used Brompton. The tube gets distorted by the heat of brazing. Installing and reaming the sleeve provides a variable thickness shim with a round hole for the seatpost.

I have had a Brompton reamer for a few years and have used it often enough on my family’s and friends’ Bromptons to (just) pay for itself. A slipping pre-reamed sleeve was the prompt.