Author Topic: Brompton seatpost shim  (Read 3316 times)

LittleWheelsandBig

  • Whimsy Rider
Brompton seatpost shim
« on: June 19, 2020, 11:29:14 am »
I need to replace the Nylon shims in my Brompton frame and in my telescopic seatpost. The shims are easily available and do not look to be inherently difficult to replace.

The frame shim is listed as both unreamed and reamed in some websites. I understand the shim should be reamed once bonded in place. I guess the reamed price is for a shop-fitted shim.

The seatpost reamer is >£100 and even I am looking sideways at spending that much for a two minute use. How necessary is Brompton frame shim reaming and is there a ghetto way of doing so?
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citoyen

  • Occasionally rides a bike
Re: Brompton seatpost shim
« Reply #1 on: June 19, 2020, 01:33:02 pm »
I was completely oblivious to this need for reaming the shim when I replaced mine, so I didn't. Couldn't possibly tell you whether doing so would have made any difference!

Bonding it in place is absolutely essential though.
"The future's all yours, you lousy bicycles."

Re: Brompton seatpost shim
« Reply #2 on: June 19, 2020, 10:48:19 pm »
Bonding it in place is absolutely essential though.

What did you use - are we talking UHU or epoxy?

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #3 on: June 19, 2020, 11:04:12 pm »
Superglue with rubber, for use with flexible materials. Brompton’s recommended glue appears to have slow gel and setting times to allow sufficient working time to reposition the sleeve and clamp it down properly. A 20g bottle for £20 is excessive for replacing one sleeve. Loctite do a 3g bottle of suitable adhesive for £3-4, which should do nicely.

I understand that earlier shims might not have needed reaming but that all current shims have an undersized bore and must be reamed. It looks like I might have to get a third expensive, unique tool or break down and go to a shop. For philosophical reasons, I really do not want to do that last option.
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Re: Brompton seatpost shim
« Reply #4 on: June 20, 2020, 07:25:23 am »
I did mine without reaming and it's just right.  I scraped all the old glue out and Argos blasted the frame before painting.  I glued the new shim with Extreme Power Glue https://www.wilko.com/en-uk/unibond-repair-extreme-power-glue-20g/p/0231136 and, after making sure there was no glue on the inside of the shim, left the seatpost clamped up overnight.

I still have a spare shim if you need it.  There were two in the pack- one has a locating lug and one doesn't.  I can send a photo of the one I didn't use.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #5 on: June 20, 2020, 08:06:28 am »
From Brompton’s instructions:
-ƒ On bikes produced after October 2002 a sleeve with an upstanding key (fig. 1) should be used, bikes produced before this date should use a sleeve without the upstanding key, when ordering a sleeve both variants are supplied.
-ƒ Two types of sleeve are available, pre-reamed (QSTSLV) and unreamed (QSTSLV-UR).
-ƒ A specific reaming tool kit (part QSTSLV-REAMKIT) is needed when fitting the unreamed sleeve.
-ƒ The replacement sleeve needs to be fitted with a specific rubberised adhesive (QGLUESS) to secure it in place.

It is difficult to find a retailer with stock of the pre-reamed sleeve (= shim). My bike is a decade old, so needs the sleeve with the key.
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Re: Brompton seatpost shim
« Reply #6 on: June 20, 2020, 08:49:52 am »
From https://azshow.info/watch/etHrXIcAz3A/brompton-seatpost-sleeve-full-procedure.html it looks like a fairly standard 32mm reamer.

Can you borrow/hire one from a machine shop?  Until a couple of years ago I could probably have borrowed one for you from work but sadly that is no longer the case.

Another option might be to buy a used reamer like https://www.ebay.co.uk/itm/Presto-32-mm-HS-machine-reamer-on-4-MT/164170009434  That has a Morse taper on it but should still be usable.  If it isn't long enough to go all the way through you should be able to bodge a drive extension onto it. 

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #7 on: June 20, 2020, 09:04:43 am »
You are right JB, the Brompton tool is a parallel 32mm hand reamer. Buying a generic one of them from China starts at about half the Brompton tool cost and goes up fairly quickly. Reaming nylon is a little different to steel and I am uncertain whether a standard steel reamer with fewer cutting edges would overcut the nylon shim (anybody here know?). Given the difference in cost (<£60) and likely delay in shipping, getting the proper tool starts looking more bearable.

I am a little pissed that Brompton deliberately swapped from user-serviceable to enforcing dealer replacement for a consumable that their own website suggests needs replacing at least annually for intensively used bikes (seems excessive, given the Folding Society folk I know). I understand that reaming every shim ensures a good fit for a mildly distorted seat tube but even so...
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LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #8 on: June 20, 2020, 09:46:02 am »
RZ, thanks for the offer. I think the second sleeve (with slot) is otherwise identical to the sleeve with a key but I’m not sure. It looks like pre-reamed frame sleeves are now unobtainable, so you may want to hang onto your spare for the next time you need one. Without the key, you just need to be careful that the sleeve slot is correctly aligned.
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Re: Brompton seatpost shim
« Reply #9 on: June 20, 2020, 10:55:05 am »
This one looks to be pre-reamed.  It has helical reaming marks inside.  Let me know if you want it - I do so few Brompton miles that I'll never wear mine out .

It also has the key.  I probably used the wrong one for my 2009 bike, not that it matters if you locate it correctly.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #10 on: June 20, 2020, 08:58:40 pm »
Thanks for the offer RZ. PM sent.
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LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #11 on: August 13, 2020, 06:05:14 pm »
A ready-reamed seatpost sleeve bonded into place and ... the seatpost slips when ridden. Yes, I have degreased the seatpost and the sleeve. The bolt is tightened as far as I dare and the seatpost doesn’t slide under its own weight when the QR is opened, which suggests it is a little too tight. There were reaming marks visible in the sleeve and I can even see the sleeve has a gap at the front of the seatpost from a reaming mark with QR closed.

Right, time to replace the sleeve with an unreamed sleeve and buy a reamer to do this properly. This bloody bike is going to be fixed, whether it likes it or not!
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Re: Brompton seatpost shim
« Reply #12 on: August 13, 2020, 06:51:36 pm »
That's unlucky.

One factor might be that I have the Brompton titanium post, which is a bit less slippery than chrome.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #13 on: August 13, 2020, 06:54:13 pm »
Such is life, in the words of that great Aussie philosopher.

It does give me an excuse to buy another silly expensive tool, which is nice.
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LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #14 on: August 26, 2020, 04:07:35 pm »
Some more Brompton heavy metal has arrived.



After picking up a couple of unreamed sleeves from Stows Cycles, everything should be sorted soon with a sleeve to spare.
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Re: Brompton seatpost shim
« Reply #15 on: August 26, 2020, 08:19:08 pm »
Bonkers design, isn't it?  The tolerances must be crap if they can't make a shim that fits straight in.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #16 on: August 29, 2020, 07:35:11 pm »
It took a couple of passes with the reamer to get the right tolerance for the seatpost to drop with the QR open but to be secure when tightened. At least it all works now.

There is little clearance between the chainring and reamer handle which made it difficult to grip the reamer tight enough to turn it. Next time I might ream the sleeve without the RH crank installed.
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Re: Brompton seatpost shim
« Reply #17 on: September 03, 2020, 06:22:19 pm »
Hi.

I would like to continue the topic.

I found some reamers on marketplace, it is not exactly like Brompton's original, but instead it is very cheap, like 15€. Total length: 26,5cm, "reamer" part is 13,5cm. What do you think, it might work? I think I just need to extend it (probably weld it and center it on a lathe?), or the length 26,5cm would be OK?



Someone on FB told be that this Acceofix shim is pre-reamed and it works fine in Brompton.


LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #18 on: September 03, 2020, 07:06:04 pm »
The factory tool has a threaded hole in the end with a single Allen bolt securing a multi-lobe handle. You might be able to do something similar. All the reaming is done from the underside of the Brompton with a plastic split guide keeping the reamer aligned in the bottom of the seat tube. That guide can be the old removed sleeve.

The Brompton seat tube is 24 cm long and the sleeve is pretty short, so it might just work with its current length, depending on how much taper there is on the end of the reamer. I had to run my reamer twice, going further the second time, because the first pass with the reamer only protruding a centimetre or so didn’t remove enough plastic.

You will also need a tube or suchlike to press against the inner wall of the unreamed sleeve while the rubberised superglue is curing (pick something with a slow set time), otherwise it won’t bond properly. The seatpost won’t fit until the factory sleeve is reamed.

If you select a sleeve that doesn’t need reaming, why worry about a reamer? Of course, the seatpost itself would work to bond the sleeve in place.
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Re: Brompton seatpost shim
« Reply #19 on: September 03, 2020, 07:50:10 pm »
"The factory tool has a threaded hole in the end with a single Allen bolt securing a multi-lobe handle."

Very good idea and it is easy to do on a lathe.

"You will also need a tube or suchlike to press against the inner wall of the unreamed sleeve while the rubberised superglue is curing (pick something with a slow set time),"

This is the small tool beside the reamer on your pic, right? If you have a little time, can you measure it for me? I might 3D print one or I do one on lathe.

"If you select a sleeve that doesn’t need reaming, why worry about a reamer? Of course, the seatpost itself would work to bond the sleeve in place."

Very good question. I don't know the main reason why Brompton stopped to sell reamed sleeves. Just to make extra work for official stores? Somebody wrote on FB that "The sleeve needs to be reamed because it is purposely made too big so that it can account for frame irregularities.". I don't know how true this is. Now I don't know If I should go with the out-of-the-box solution from China or go with the official way. What do you think about this?

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #20 on: September 03, 2020, 08:20:34 pm »
I tried a factory pre-reamed sleeve and the seatpost slipped, hence why I bought the reamer. Everybody else I know who has fitted a pre-reamed sleeve had no problems. You pays your money and you takes your chances.

Welcome to the forum, what brought you here?
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Re: Brompton seatpost shim
« Reply #21 on: September 03, 2020, 08:29:00 pm »
Well, thanks for the answer.  :thumbsup: If you don't forget and if it's not a big ask, please post the size of that small tool later.

Re: Brompton seatpost shim
« Reply #22 on: September 04, 2020, 06:37:57 am »
LWaB, did you check the actual size of your seatpost?  Just in case this is an unfortunate clash of tolerances, with the post being slightly undersized?

The glue is probably the unknown in the equation.  Brompton should be perfectly capable of making a seat tube to an accurate ID, since everyone else can (the "frame variation" excuse is BS from them).  However, if you're going to stick a shim in with glue, it all becomes a bit random, especially if you are cleaning old glue out and putting new glue on top.

A glueless insert, secured by a lug at its lower end to stop it popping out with the seatpost, would seem to be a sensible way forward.  But Brompton don't move forward - no need to, when they can sell them faster than they can make them.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton seatpost shim
« Reply #23 on: September 05, 2020, 11:39:27 am »
The frame sleeve is about 67mm long and the Brompton bonding mandrill is 31.0mm diameter and thick-walled steel.

The SH extended post is a tiny bit larger diameter than my telescopic post. My telescopic post could just be twisted by both hands without a saddle on it.

Normal frames get reamed after fabrication to get a snug fit for the seatpost. Normal 28.6mm Reynolds 531 seat tubes theoretically need a 27.4mm seatpost for a snug fit but heat-induced distortion means that a 27.2mm seatpost is the correct fit. Very rarely, a silver brazed frame will need a 27.4mm seatpost instead. I have only seen that once.
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Re: Brompton seatpost shim
« Reply #24 on: September 05, 2020, 07:31:01 pm »
Tony Oliver frame?
And Darkness and Decay and the Coronavirus held illimitable dominion over all.