The big advantage that the older style threaded headset has over new Aheadsets is that it is very easy to adjust the stem height without replacing any parts.
Adjusting stem height
Follow these instructions to change your stem height. Then check that the stem is tight by standing in front of the bike, holding the front wheel between your knees. Try to twist the bars around. If you can move them, the stem bolt is too loose. Retighten. If the stem is tricky to tighten, it may indicate that the steerer tube (the central part of the fork that extends up through the frame and onto which your stem is bolted) is damaged. Alternatively, the wedge at the bottom of the stem, the one that is pulled upward when you tighten the stem bolt, may have become twisted in the steerer tube. Either way, if you can’t tighten your stem, get your bike shop to have a look at the stem and steerer tube, and to replace the forks if necessary. Also make sure that the front wheel is pointing straight forward; if not, loosen the stem bolt, twist it so the wheel and bars are at 90 degrees, and retighten.
“If you can’t tighten your stem, get your bike shop to have a look at the stem and steerer tube”
Step 1: Undo the expander bolt at the top of the stem. This almost always needs a 6mm Allen key, but you might need to prise off a rubber bung first. Undo it in four complete turns.
Step 2: As you turn the bolt, the head rises up out of the stem. Tap the Allen key with a rubber mallet or block of wood, so that the Allen key drops down flush with the stem again. This releases the wedge that holds the stem in place.
Step 3: Once the stem is loose, you can adjust its position. Make sure you don’t raise it above the safety mark – an arrow or a row of vertical lines around the stem. They should not be visible; instead they should be hidden inside the headset. Retighten the 6mm Allen key bolt firmly.
The main reason for the demise of the once ubiquitous threaded headset is that it requires a pair of expensive spanners to adjust it – unlike the Aheadset, which can be adjusted with an Allen key.
Tools for threaded headsets : adjusting stem height
- 6mm Allen key
- If the expander bolt is wedged firmly, a plastic hammer or a block of wood is needed to knock it down
Tools for threaded headsets : adjusting bearings
- Ideally, two headset spanners – the most common size is 36mm, although older, 1-inch headsets need 32mm spanners – it is possible to use an adjustable spanner on the top lock nut instead of a headset spanner, but take time to tighten the spanner carefully onto the nut flats, since they are soft and easily damaged
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Aheadsets : cutting off excess steerer tube”