Monday, November 14, 2011

Cross bike update - Headsets Assemble!

The bike fairy came yesterday and gifted me with a seatpost, a stem and a headset! I am happy with the seatpost, it's a 2 bolt micro adjust. The stem is square-ish, and looks like it's going to be real stiff. The headset is also great; it took a little experimenting to figure out what parts went where (it came with no instructions) but it's looking good.

30.2 Seatpost Stem

I'm stoked to have the seat post that is nice looking, light, and wasn't terribly expensive. It may prove harder to be to find the right size seatpost clamp. I'm probably going to end up heading into a bike shop and ask what to do.

What size clamp...?

The headset is a newer kind that employs a sealed bearing system. This takes similar advantage of sealed bearings as an external bottom bracket; lighter, more simple and far more resistant to moisture. Here is the whole headset laid out on the steer tube:

fork crown | race | bearing | bearing | compression washer | top cap | star nut

These are the parts for this headset, and this is what they do:

fork crown - the race is pressed onto this part of the fork
race - the race fits the crown, and is specific to the headset bearings
bottom bearing - most of the weight is carried by this bearing (this is why many newer frames run a 1.5" lower bearing)
upper bearing - less load bearing (ha)
compression washer - this keeps the steer tube tight against the bearing
top cap - this part has a rubber washer to keep moisture out of the headset, and a guide for the brake cable
star nut - part of this goes into the steer tube and locks in place (the part that looks like a star) By tightening the hex bolt through the top cap, you compress the whole headset tightly

The bearings fit into the frame in a very sexfull way -


The top of the head tube is machined to fit the bearing very closely. The bearing is chamfered to match the machining of the inside of the head tube. When installed it looks like this:

bearing installed

It's a satisfying system, and far less opportunity for looseness than a classic headset with cups that are pressed into the head tube. There are a few considerations left with these parts:
- the steer tube of the fork will need a few inches cut off and some spacers to get the stem at the right height.
- the star nut needs to be installed with some care so it's straight and secure
- the race has to be pressed onto the crown
- the aforementioned seat clamp

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