The special thing about this Haul-A-Day headset and fork design is that the handlepost can be inserted all the way through the middle of the steerer tube. This allows for a great range of handlepost height adjustment.
However, this also means that there is no traditional star nut inserted into the middle of the steerer tube, which is necessary to pre-load the headset in combination with the top cap. Bike Friday recommends using their special headset tool to pre-load the headset.
The instructions for using this special tool can be found at this link (Page 28).
https://www.bikefriday.com/folding-bikes/wp-content/uploads/2018/06/HaulaDay.manual-2018.pdf
This tool basically compresses the headset from the outside, instead of from the inside with a star nut.
I don't have this special tool, so I have to think of some other ways to tighten the headset. I used an expander plug, which is commonly used for carbon steerer tubes, as it prevents damage to the inside of the steerer tube, unlike a traditional star nut.
Theoretically, once the expander plug is mounted tightly inside the steerer tube, I can pre-load the headset by using normal stem spacers and the top cap. It will work the same way as standard steerer tubes and stems.
However, in reality, once I tighten the top cap, the expander plug will be pulled out of the steerer tube, instead of pre-loading the headset bearings. No matter how much I tighten the expander plug, it does not have enough friction to stay inside the steerer tube. So this idea does not work.
Standard expander plug, used to allow the top cap to be tightened to pre-load the headset. But it does not work as there is not enough friction between the expander plug and the inside of the steerer tube.
The other way is to compress the headset from the outside, by pressing down on the top cap and pushing up at the bottom of the fork. I would need something similar to the Bike Friday special tool. It mainly consists of a super long bolt, so that when tightened with a nut, it will pull the whole headset together.
While looking through my spare parts, I found that the quick release axle may work! It is basically just a long bolt with a M5 thread at the end. However, using the longest quick release axle that I have (for rear 135 mm OLD), it is still not long enough to pass through the entire headset and stack of spacers.
Quick release axle inserted through the top cap, with the spacers on the outside to ensure that the compression force is transmitted through the headset bearings.
However, since the quick release axle is not long enough, I need something that can be inserted into the fork, and then thread onto the end of the quick release axle.
This is where I got lucky, as I found a quick release axle accessory mount, which is usually used to mount lights on the quick release axle. This mount replaces the standard nut on the quick release axle, so it also has an M5 thread.
Example of how the quick release axle mount is normally used.
By sheer luck, this mount fits nicely into the fork, and the lip at the end of the mount fits around the circumference of the fork hole so that it is well supported. The dimensions of this mount fits the fork so well that it seems like it was designed for this purpose!
The mount fits nicely into the bottom of the fork.
The lip of the mount is stopped by the circumference of the bottom hole on the fork. This is just perfect!
Inside the steerer tube, the quick release axle will thread into the M5 threads on the mount. By tightening this, it will pull the headset together and apply the pre-load.
How the DIY headset tool works! It is easy to adjust and basically works the same way as the Bike Friday special tool. Once the compression is done, tighten the clamp bolt to fix the steerer tube in place.
The DIY headset tool consists of the quick release axle, the mount, the top cap, and a bunch of stem spacers.
That's very clever, but I can't find that Far and Near QR based light mount, or any other one with threading at the end.
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