Author Topic: Brompton seatpost shim  (Read 346 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?
Wheel meet again, don't know where, don't know when...

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.

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.
Wheel meet again, don't know where, don't know when...

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.
Wheel meet again, don't know where, don't know when...

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...
Wheel meet again, don't know where, don't know when...

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.
Wheel meet again, don't know where, don't know when...

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.
Wheel meet again, don't know where, don't know when...