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Brompton rear hinge bolt size / thread pitch

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Brompton rear hinge bolt size / thread pitch

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Old 09-02-14, 09:34 AM
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chagzuki
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Brompton rear hinge bolt size / thread pitch

What are the specs for the Brompton rear hinge bolts?
I plan to try this method for replacing the parts:
https://www.youtube.com/watch?v=8L2SXHDLffM
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Old 09-02-14, 09:58 AM
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fietsbob 
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what do you want to accomplish ?

Take it out 1 of them And look .. or, The company will reply when you ask them directly.

yes the video showed how to remove both to pull the rear portion

the bolt nut and washer is to keep the other side from spinning the hinge bushing-axle, as they unscrew the other flat head

I'd guess .. 6mm.
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Old 11-15-17, 02:11 PM
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Mine won’t budge, you have to drill them out if they won’t budge
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Old 11-15-17, 05:35 PM
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Indeed: what do you want to accomplish? In many if not most cases the bolts won't come out as easily as shown in the video as they are glued in - therefor with a high probability you'll have to drill them out. Once they are out the question is why. In most cases it is because the rear hinge is worn and in this case the fun just begins and there's a lot that one can do wrong when replacing the bushings. I.e. you need a proper reamer for that. Therefor it is normally easier, more successfully AND cheaper to give the bike to an experienced mechanic for those tasks.
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Old 11-15-17, 05:59 PM
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Originally Posted by chagzuki View Post
What are the specs for the Brompton rear hinge bolts?
I plan to try this method for replacing the parts:
https://www.youtube.com/watch?v=8L2SXHDLffM
I watched the exact same YouTube video and have done four Brompton now.

Tool: 5/32" hex bit or key for rear hinge countersunk set screw
Washer: OD20 ID7 at least 5mm thick to act as friction washer. I found thinner washers dished when torquing up the "locking" screw. I turned a couple 7mm thick washers and roughening the surface to grip the flange.
Locking Bolt: 1/4" x 28TPI x 40mm UNF. Buy high quality 8.8 bolts. I used socket head engineering bolts.
Nuts: 1/4" UNF

It may require a couple attempts to break loose the second hinge set screw. It has thread locker applied on the threads and the countersink during assembly.
It requires a surprising amount of torque to lock the pin to prevent it from spinning when breaking free the second hinge screw.

EDIT: I needed to this as I was installing Vostok rear triangles. The task should be well within the capabilities of a competent mechanic.

Last edited by MultiplexMan; 11-15-17 at 06:02 PM.
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Old 11-16-17, 03:20 AM
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Originally Posted by theador View Post
Mine won’t budge, you have to drill them out if they won’t budge
So I got the rear triangle off last night. I'm getting the frame resprayed and I will replace the hinge spindle and bolts.

I used the method listed on one of Bromptons how-to articles. Essentially you cut out the plastic washers (I used a junior hacksaw) and then using the gap available, cut the bolts.

Article found here:
http://www.brompton.it/rivenditori/s...es/ds-rhin.pdf

I resorted to this technique after snapping a heavy duty socket allen wrench trying to get the screws out.

Last edited by theador; 11-16-17 at 03:25 AM.
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Old 11-16-17, 04:04 AM
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I removed the rear triangles on two of my Bromptons recently and I only needed 2 allen keys. I used an allen key on each hinge bolt to try and loosen them simultaneously. Although it took some force, one of the bolts came loose each time leaving the other one spinning within the spindle. I then cleaned off the bolt, reinstalled it into the spindle fairly tightly (> 10 Nm) and then used both allen keys again and which in both cases the second bolt loosened first. This seems to work because the recommended torque of the hinge spindle bolts is only 10 Nm so when you reinstall the first bolt past this torque, the second bolt seems to come first (even with Loctite surprisingly). Of course you probably would be better off not reusing the bolts and spindle after this.

I wanted to use the bolt and washer trick but I didn't have a washer/washers thick enough to not get deformed when torquing the bolt.

Last edited by leoho5; 11-16-17 at 04:11 AM.
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Old 11-16-17, 05:51 AM
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This method didn't work for me; I think it's luck as to how strong the threadlocker is. I tried drilling a bolt out and it was a nightmare. In the end I cut through the spindle with a saw, not ideal as I scratched the inside of the rear frame slightly (though it doesn't show when reassembled). I've employed weaker threadlocker and expect it will be quite easy to do the next time.
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Old 11-16-17, 08:27 PM
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Would heating up the bolt with a soldering iron help? I read that it might work with blue loctite.
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Old 11-17-17, 02:23 AM
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Originally Posted by dahoneezz View Post
Would heating up the bolt with a soldering iron help? I read that it might work with blue loctite.
Blow torch maybe but you’ll strip the paint before loosening the bolt
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