From: jackson@ponder.csci.unt.edu (Bruce Jackson)
Subject: Re: HEADSETS - stack ht, diameter
Organization: University of North Texas, Denton
Date: Tue, 8 Sep 1992 16:20:25 GMT

In article <1992Sep8.095418.1@mscf.med.upenn.edu> ross@mscf.med.upenn.edu writes:

>	- Ordering a new headset.  I would like to buy a decent sealed
>bearing headset to replace the piece of crap headset that the bike came
>equipped with.  I need to match the internal diameter of the head tube
>and also the stack height.  Obviously I can't get one with a higher stack
>height but what about a lower stack height.  Is filling the extra space with
>washers acceptable.  What type of washers should be used?  I don't want to
>take the step of cutting the fork.

The shop that sold you the bike should be able to tell you the I.D. 
of the head tube and the O.D. of the fork crown since they probably
have replaced the head parts on some of these bikes by now.  You
can carefully measure them with calipers (a good tool to own btw).
You can measure the stack height by removing all of the head parts,
placing the steerer into the head tube with the crown face against
the head tube face, and measuring the distance that the streerer
sticks out past the top of the head tube.

>	Are there any manuals that have specs for different bikes.  I've
>got a Specialized Hardrock.  Isn't there someplace where I can find out
>the internal diameter of the head tube and the stack height of the original
>equipment headset.  Local bikes shops are ultra uncooperative on this one
>(like I'm treading on some sacred ground - just bring in your bike and your
>$$$$$$ seems to be their attitude - hey, I'd be willing to buy the part and
>the tools from them).

Like I was saying, the shop should know off hand or at least have it
written down somewhere.  Sutherlands probably wouldn't have info that
recent so there probably isn't anyplace where you can simply look it
up.  Again, a good set of vernier calipers are a good investment for
basement mechanics. (don't get the cheesy plastic ones however, spend
money for precision tools.  You will have to be withing .1 mm.)

>	- Tools.  How many, what type of tools are needed to remove the old
>headset.  I know I have to remove the stem (no problem) and then loosen the
>locknut (headset wrench).  But for removing those fixed cups?  I saw two 
>types of tools.  One looks like a chisel that you put up through the headset
>and then knock out the cup from the back.  The other one looks like a 
>"U" (but with square edges).  Are both of these tools needed or only one?
>Since I'm trashing the headset that I'm removing, is there a less expensive
>way of knocking it out (say with a screwdriver) or do you risk damage to the
>bike with this method.

The drift to remove cups looks like a rocket.  The tool to remove the
race on the fork crown is `U' shaped.  I'd buy both if I were you.
I don't know how much you are risking damage your bike with makeshift
tools but my attitude is any job worth doing is worth doing right.

>	- Installation.  Should I get that special tool that sits in the cup
>which you then hit with a rubber mallet or is the method of putting a piece
>of wood over the cup and then hitting it also ok.

The first time you install a new headset in a production bike the head
tube and fork crown should be machined so that the head parts will be
perfectly parallel to each other and perpendicular to the steerer and
headtube.  For the first overhaul have the frame and fork faced at a
good shop with the Campi tool kit or equivalent tools.  Make sure that
the shop knows what they are doing.  A bad shop can do quite a bit of
damage.  Some shops never have their tools sharpened since this is very
expensive.  These dull tools do not cut accurately.  The cups that go
into the head should be pressed in, not hammered.  They have to be seated
on the faces with a great deal of even pressure.  If you insist on doing
it yourself put the parts in a vise with wood over the jaws and press
them in that way.  I don't know off hand how much the special tool to
press in the cups cost but they do look expensive.  The race that goes
on the fork crown is seated with a slide hammer that goes over the
steerer.

A well installed headset will last at least twice as long as a poorly
installed one so do the job right!

good luck!

Bruce  -  jackson@cs.unt.edu


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