The Magistroni headsets use 5/32in ball bearings.
Hilary Stone, Bristol, British Isles
Mark Bulgier wrote:
> Lucas Murray wrote:
>
>> I'm putting together my Sieber track bike and need to
>> know what size bearings my headset takes. Anybody know
>> off the top of their head? Its this model.
>>
>> http://www.blackbirdsf.org/
>
> I don't know the answer, but here's how I'd go about it if you don't get
> a definitive answer from a real Magistroni guru.
>
> Nine out of 9 headsets use one of three sizes: 3/16", 5/32" or 1/8". (I
> know it might seem strange that an Italian part would use
> fractional-inch balls, but they really do, exceptions are exceedingly
> rare.)
>
> Actually 3/16" is pretty unlikely for that old thing, so maybe you could
> skip 3/16", then you've narrowed it down to just 5/32" or 1/8". But
> here's the basic rule (assuming yours has cup/cone bearings -- the
> following is _not_ true for the v-groove headsets like the Stronglight
> V4 and some Italians):
>
> With the headset cup clean, devoid of grease and grime, try one ball,
> the largest size first.
>
> The curvature of the concave surface of the ball race in the cup must be
> larger than the ball, so the ball touches in only one (theoretical,
> mathematical) point. If the curve on the cup is larger as it should be,
> then the ball will be able to travel a tiny bit up and down the curve in
> the direction perpendicular to the race. If the ball is the same size
> as the curvature of the cup or larger, then it'll touch in two places
> and will only be able to move exactly in the direction of the race, like
> it's locked on a rail, no wiggle room in the perpendicular direction.
> You need the wiggle room.
>
> If the ball is too large, go down to the next smaller size.
>
> If the ball seems to fit the curvature of the cup properly with some
> wiggle, then load the race up with grease and a full complement of balls
> (as many as will fit), as long as that leaves a little extra room, like
> a fraction of a ball. If it completely fills it up with no extra room,
> take one ball out. It's safe to have one ball too few, and terrible
> awful to have one too many, so when in doubt, take one out.
>
> Feel for roughness or fit problems. Roughness often means balls hitting
> somewhere they're not supposed to (balls too big), or cup and cone
> coming into contact with each other (balls too small). The bottom of
> the cup should come down low enough on the cone that there is only a
> very thin gap (where water and grit can get in). If the balls are too
> large it'll lift the cup up too high, and on some headsets that'll be
> noticeable as a larger than normal gap. Similarly, balls too small will
> let the cup come down too low over the cone, to where the cone looks
> recessed up into the cup.
>
> Some experience with what a properly-assembled headset looks and feels
> like will go a long way to setting your mind at ease that you've got the
> right size.
>
> Mark Bulgier
> Seattle, WA USA