SkinGriz

I have 2 bikes with 21.1mm stems.

So I don’t need to drive the bearing cups out…

Is the head tube on an old Schwinn also a thinner ID? Or is the difference made up with different cups, cones, and bearing sizes? Thank you.

dedhed

The standard Schwinn size between 1966 and 1982 for headsets are.

Crown race ID (inside diameter) 26.4mm
bearing cup OD (outside diameter) 32.7mm
quill diameter OD 21.15mm or .833
thread pitch 24 TPI (threads per inch)
1" old BMX threaded headset is what you need.

May need your old top nut with .833 hole

well biked 

It's just the 21.15mm inside diameter of the steerer tube and the 21.15mm diameter quill stem that are oddities. Schwinn did this so that the wall thickness of the steerer tube was thicker (at the expense of smaller diameter quill stems).

SkinGriz

If I wanted to use a 1” fork do you think I can just drive out and replace the bearing races?

Thank you.

dedhed

The Schwinn steerer tube is 25.4mm OD same as any 1", but it does have thicker wall, hence the .833 quill stem and should be 24 TPI

well biked 

Again, you already have a 1" fork,. But if you want to get away from the oddity of the 21.15mm ID of the fork's steerer tube and the 21.15mm quill stem by replacing those items with the more common 22.2mm ID fork and 22.2mm quill stem, all you would need to replace in regard to the headset is the locknut. The ID of your current locknut matches your 21.15mm stem, so a 22.2mm stem won't fit. You would need a locknut with an ID matched to the larger diameter 22.2mm stem. If you want to replace the whole headset with one designed for a 22.2mm quill, you can do that, too, along with the fork replacement.

SkinGriz

Thank you.

SkinGriz

If the steering tube wall thickness is increased maybe I can tighten the quill like crazy and still avoid bulging the fork.

dedhed

Or take a file to the existing one

Andrew R Stewart 

Why would you want to tighten the stem's quill bolt "like crazy"? Is there a problem with the current set up not keeping tight or does the stem move about while riding? The usual way to tighten a stem is to only use enough torque to maintain the stem's position during the usual riding situations. There's a philosophy about this called "race tight". Parts like stems and seats are only tightened enough to not move under usual forces but can rotate upon impacts (crashes) and thus be able to be realigned w/o tools so the rider could continue their race.

One more tidbit about steel, strength and wall thicknesses is that those thick walled steerers (25.4mmOD and 21.1mm ID) are generally made of rather low strength steels (which costs less to source and is faster to fabricate than high strength 4130). I would want to push the math to find out if these thick walled steerers are actually more bulge resistant. I've seen more that a few steerers with damage from bad stem use/maintenance. The first time was when I was 10 years old and my Columbia balloon tire bomber's steerer broke off completely just above where the stem's wedge was. (And I weighed all of about 60 lbs back then). Others seen in my LBS life had both bulged and broken OEM steerers, most all IIRC were on low cost bikes of both 22.2 and 21,1 stem fits. This might be due to this grade of bike often isn't as well assembled/maintained as better bike shop grade bikes are. I have seen good quality replacement forks suffer from cracks in the threaded portion due to the stem not being inserted far enough and the wedge was tightened where the threads are. Andy

SkinGriz

Points taken and considered. Thank you.