The Servicing of an Internally Geared Hub

There are many benefits of using an internally geared hub. For the most part, the unit is sealed off the elements, you can use them in a belt drive system, they shift really fast, etc. When we get one of these hubs from Shimano, or on a built bike, they come packed full of grease. With most Shimano internally geared hubs, grease is used to lubricate moving parts. However, here in Minnesota, extreme temperatures can change the way grease acts, especially when you're dealing with gears only a few millimeters in diameter.

Today we will talk about how to clean, service, and re-lubricate (with winter in mind) a Shimano Nexus 8 speed internally geared hub.

First, we need to remove the external components. Turn the shift mechanism locking to the left and the shift assembly slides right off.

Remove the cog snap-ring. This thing can be a huge pain. Unhook it from its groove and get a screwdriver under it. From there, all you have to do it walk it around till it comes off. I like to wear safety glasses of some sort when doing this. Snap-rings can be unpredictable at times.

The cog slides right off from there.

After the cog comes off, there is a dust shield and seal exposed.

Once removed, the drive side is now prepared for the cartridge to come out.

This bike is equipped with a roller brake. It's almost like a drum brake that's actuated with a hexagonal nut looking thing that 6 rollers rotate around pushing pressure plates against the inside diameter of the braking surface.

There is one nut that holds the assembly to the hub shell. Once that's removed, the whole brake comes off.

We now have access to the wench flats of the cone and lock-nut. These can be completely removed...

... And the internals are free of the hub shell!

The dirty, greasy parts get a nice hot bath in the parts washer. I usually let the cartridge sit for an hour or so to allow the old grease to break down.

Here is an exploded view after the parts are all cleaned.

Since when has Shimano made ice cream topping???

Must be "Blue Razzzberry."

The cartridge gets soaked till it's good and saturated. I usually wait till the bubbles subside.

Allow the excess to drain.

Clean the inside of the hub shell.

Apply grease to the bearings and clutch rollers. I also inject 3cc or 4cc of the special Shimano oil (ice cream topping) between the gears before putting everything back together.

Reinsert the cartridge and wipe off the excess grease.

Re-adjust bearing on the non-drive side till there is no play.

Install dust seal.

Grease back of dust shield and reinstall.

Grease the back of the cog and reinstall (We have had issues with these making noise, and grease seems to solve the problem).

Realign red dots with red, yellow dots with yellow...

... And rotate lock-ring to lock the shift mechanism in place.

It's good practice to lubricate the roller brake regularly. Squirt some special roller brake grease in the grease port.

Loosely install the roller brake. Tighten the drive side axle nut, align the reaction arm, then tighten the roller brake nut to fix it to the hub.

Seat the axle in the dropouts and fasten both axle nuts. Align belt if applicable. Check all the gears to make sure there are still 8 of them. If there aren't as many as when you started, something went wrong. Shift into 4th gear and use cable tension to align the two yellow marks in the window.

After performing this service, the hub felt like it shifted faster and more crisply, especially in the extreme cold. One of our year-round commuting employees, Ben, who uses the same hub described the overhaul to make the shifting "less gummy and more direct. It gives me all of it," he concluded. I'm not really sure what that last part means, but it sounds pretty positive.

Preparing a Frameset for Building

When building a bike from the frame up, there are certain preparations that should be made to the frame. When a frame is painted or powder-coated, there can be build-up left in and on the headtube, bottom bracket shell, and seat tube. Precision components can be very sensitive to imperfections in frame construction, causing premature wear, binding, and noise.

Before installing any seatpost into the seat tube, it's a good idea to remove any burrs that could scratch or gouge the seatpost.


When the manufacturer makes a relief cut in the seat tube, it often leaves big burrs.


A Flex-Hone gets put in a drill chuck and is spun inside the seat tube to clean burrs and polish the tube.


There is still some excess paint left in the seat tube, but the sharp edges have been taken care of.


The next order of business is to take care of the paint on the faces of the bottom bracket shell. With most external bearing systems these days, the slightest imperfection can cause issues.


Excess paint on bottom bracket shell.


Here is the tool we will be using for this process. This tool does two things, chases the bottom bracket threads and faces the bottom bracket shell.


The tool uses a guide that runs through the center to make sure the threads and face are cut square to the center line of the bottom bracket shell.


Since the frame is brand new, the taps go in pretty easily.


Once the taps are in and recessed within the shell, we can set the tool up with the facing mill.


The tool detaches from the tap and the facing mill snaps right in.



Always apply cutting oil to any tapping/milling/cutting operation.


The shell is 95% faced. You can see the small amount of paint still remaining in the 10 o'clock position. Once this little bit is removed, the shell will be completely faced.


After: A nice, fresh, clean, perpendicular, bottom bracket shell face.


Time to do the same thing for the head tube.


Here is the tool we will use on the head tube.


This tool will ream the inside diameter of the head tube to the correct diameter for the proper headset to fit as well as facing the top and bottom surfaces.


This tool uses a cone to center itself on the side its not cutting.


Nice looking spirals of material indicate that the cutting tool is sharp and material is being removed with ease.


Once the top is finished, the tool is flipped and the bottom of the tube is faced and reamed.


I had a pretty nice spiral of paint on this one, so I grabbed another shot.


After: A nice, clean, perpendicular, faced and reamed head tube.


The final step we will talk about today is milling the fork crown.


There is random paint build up on the surface of the fork crown that the headset race will contact. To ensure good headset race contact, we will face this, as well.


Here is the cutting tool we will use for this operation. The cutting teeth are slightly out of focus. The more important part of this tool is the blue sleeve inside. This is the guide that will make the tool cut square to the steer tube.


Again, this tool provides two functions. It mills the outside diameter of the fork crown to the proper thickness and faces the crown to provide a smooth flat surface for the race to rest.


After: A clean, smooth, fresh, square surface for the headset race to sit.

Most aftermarket parts companies highly recommend facing before installing their components; Chris King, Cane Creek, Shimano, to name a few. As you can tell, there are quite a few, fairly expensive cutting tools required to do a proper frame preparation. Usually, shop rates are fairly reasonable to have this done to your bike. It is a great idea to do this anytime you install a new headset or bottom bracket, too, if it's never been done before. Your components will thank you.