Headset Maintenance, Replacing a Threadless Stem

Due to it’s smaller frame size, my mountain bike is a super-fun machine, able to be manhandled on the trails with ease. Over the past two years of ownership, I’ve been thinking of lengthening some components to spread out my riding stance a bit, since it can be a little cramped. I was at Natural Cycle in Winnipeg, a local new and used bike store and repair shop, and was looking for a longer stem and seat post. The shop employee pointed me to this Kona aluminum stem, hanging at the very back of the rack.

Longer Kona stem 120mm to replace stock 75mm stem.

Longer Kona stem 120mm to replace stock 75mm stem.

When he handed it to me, it practically jumped right out of my hand, it was so light! She was a beaut and a steal at $8.

I’m very pleased with the folks at Natural Cycle, because they give great advice and will help you find what you need, either new or used. I read later that their employees are not sales people but all of them are bike repair technicians, so they know their stuff.

I’ve never replaced a threadless stem before or overhauled my headset, so I did some research in bike repair books from the library and on Sheldon Brown. Then I dove right in. I won’t list all the details (even though I’m a very detailed type of guy) because the Sheldon Brown article is very thorough. I’ll explain a bit about how I overhauled mine and the order in which the parts came off.

Disassembly

There are two main sets of bolts that hold together the whole steering assembly on a threadless headset: The top bolt, that goes down into the nut pressed into top of the fork, and the side bolts on the stem itself. The top bolt is only used for adjusting the play in the bearings and not for holding everything together, while the bolts on the stem are used for locking everything in place once adjusted. The side bolts only need to be loosened, but the top bolt has to come completely out for the steering fork to drop out. There will be spacers below and possibly above the stem that will be loose once the fork is removed.

I left my brake cable attached and just moved the fork (with wheel removed) onto my “bench” right beside the bike. Since I was replacing the stem, I also removed the stem from the handlebar, and tied the handlebar up to the rest of my bike frame.

Here are the bearings, spacers, etc. in the order they were assembled. The two bearings are the inner-most parts, on either side of the bearing cups pressed into frame. Again, the details on Sheldon Brown’s website are a great reference.

The order and condition in which spacers and bearings came off

The order and condition in which spacers and bearings came off

Cleaning

There are many ways to clean the parts, but some sort of degreaser is definitely a must. I would like to have a citrus-based degreaser, but so far haven’t found any. I used Varsol to clean all the bearings and parts. I poured a bit into a yogurt container and washed all the parts, making sure to get all the old grease out of the bearings. A clean rag was used to dry everything and check that there was no dirt left. If you’re keeping the bearing cage (Sheldon Brown explains why you might want to remove it and use loose bearings), make sure to get in between the bearing balls with a small brush. Here are the clean parts and the order they came off the bike (the spacers shown on the right side of the stem were actually under it).

General stackup of the whole assembly.

General stackup of the whole assembly.

Close up of bearings and parts, cleaned.

Close up of bearings and parts, cleaned.

Inspection and Replacement

I inspected all my parts based on website and book advice and found that my bearings were nice and shiny, and there was no pitting or bumps in my bearing races, either on the fork or the cups in the frame. I did bring my bearings to the bike shop, thinking I would ditch the cage and fill up the space with just bearing balls (minus one) but the advice I got was that my bearings were in good condition. In addition, I could keep the cages if I had no dents (brinelling) in my bearing races. So I kept all the parts as-is and reassembled with my new longer stem.

Reassembly

Reassembly was pretty straight-forward. I followed my photos for reference and put everything back in the order it came off. Hey, the pics aren’t just for you guys! I thoroughly packed the bearings with multi-purpose bearing grease, and set the dust cap and lower bearing on the fork crown before inserting it. Then the top bearing, dust cap and compression ring went in, followed by the stem and top cap. If you’re not sure which way the bearings go in, just assemble them dry and test fit. If things grind, they’re on backwards. Only the balls should be touching the bearing races, the metal cage shouldn’t rub anything.

Clean bearings and parts in the order they went back on.

Clean bearings and parts in the order they went back on.

During reassembly, the thing to remember is that the bolt in the top cap does the job of adjusting the bearings and how loose or tight the steering is. If there is an incorrect number of spacers and the stem sits too low (below the steerer tube of the fork), the top cap will not put tension on the assembly and the fork will be loose. So the tube on the fork (gray part, above) needs to end up a bit below the top of the stem so that there is some space to take up by tightening the top cap. I made my adjustment tight enough that the stem/fork didn’t wiggle, but loose enough that the steering assembly would turn side-to-side when I tilted the bike left and right.

Once happy with the bearing adjustment, I made sure the handlebars were straight and snugged up the two bolts that clamp the stem to the steerer tube.

Now, clamping the stem to the steerer retains the bearing adjustment and keeps the whole assembly tight. Do not use the top bolt to do any more adjusting unless you first loosen the stem bolts! All you will do is strip the threads of that star-fangled nut inside the tube and you’ll be off to the bike shop to get them to replace it. Before I knew better, I went around tightening all the bolts on my other bike, including the top cap, thinking it would tighten up my steering. It didn’t; luckily it also didn’t strip.

I’m pretty sure you can safely loosen the top bolt and nothing will change in your adjustment; I backed mine off and lined up the label on the top cap so it looked “purdy”, then snugged the bolt a bit. People have replaced the top cap with things such as thermometers, but if it needs adjustment I think you need to put it back.

Finished installation.

Finished installation. Here you can see spacers below stem, stem with the two clamping bolts, and finally the top cap that allows for adjustment. Note lettering on top cap is lined up with stem, this is very important for OCD folks but has no bearing on the bike performance.

So now I have a longer stem on my bike, which allows me a more comfortable riding stance. So far, on commutes it’s been pretty good, although I noticed the bike was tending to lean one way when riding with no hands, so maybe I need a slight adjustment of the steering still. I haven’t had the chance to do any tight single-track to see how the bike handles in the twisties, but when the river goes down and the mud clears up I’ll be out there for sure!

Bike overview with longer stem installed.

Bike overview with longer stem installed. Also got a longer seat post. Looks funny way up there, but it’s good for longer rides.

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About Lightning McKurt

I am a married man, a follower of Jesus, a Mechanical Engineer, and a lover of cars, cycling and music.
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