Sturmey-Archer FW 4 Speed Stripdown

The Sturmey-Archer FW four speed gear was invented during the second world war and brought to the market in 1946. Sturmey-Archer's publicity material stated that:

"It will be of particular interest to those cyclists who consider that the high gear in the AW wide-ratio three speed is too high, and the low gear not low enough."

This is true- just. The FW has only a very marginally wider range than the AW, a few gear inches. But it does have smaller jumps between gears and a lower gearing overall. The reason is that the FW is actually a five speed gear that does not use it's top gear for reasons of simplicity of operation. They could not think of a good way to use two cables to operate the higher gear until some years later. Instead, a single trigger was designed to pull the gears in sequence from one end making use of a clever balance of spring force.

In fact, the FW is essentially an AW with an "underdrive". This takes the form of a second sun gear that can be switched in and planets with two different diameters, joined together, to mesh with the new sun. These are called compound planets. Now, if the second sun is engaged when the gear is in the low gear position, what we get is a 'super-low' or underdrive. That is the first gear of the FW. Conversely, if the second sun could be engaged in high gear, we would get a 'super-high' or overdrive. This latter ratio is what all FW's are capable of but never had, sadly.

One great thing about the Sturmey-Archer FW and AW is that they are so well-designed for maintenance. Nothing on them is difficult to remove or fiddly. The job is really one of just taking everything off, cleaning it and putting it back together again like a sort of puzzle. Personally, it is a task that I really enjoy. And if you meet a part that is not in such great condition, you can usually substitute it with a similar part from another hub. Even in a neglected condition, Sturmeys usually run without trouble, but all hub gears love to be overhauled. They run beautifully smoothly and silkily afterwards.

From a practical point of view, taking the FW apart is not much more complicated than taking apart an AW. It is essentially the same process until you reach the axle. An AW has a single sun fastened to the axle- there's no more to do. The FW on the other hand has several moving parts assembled on it's axle and a long, thin spring inside. There's often no need to take the axle assembly to pieces but if you have gone that far, why not examine, clean and lubricate everything? However, please do pay attention to the order that you take off the parts and lay them all out methodically.

You can do it on the kitchen table (if you are single) but it is very much easier if you have a vice handy to fasten the axle pointing vertically upwards. Also, if you can get hold of a Sturmey-Archer cone spanner, the process of bearing adjustment is simple. And this should ideally be perfect.

Click on the first photograph to start the slideshow. Click the small square to pause.

This is a typical 1960s FW from a Moulton Deluxe. Grip the flats of the axle on the drive side in a vice.

If you have a Sturmey Archer cone spanner this makes removing the locknut on the left side easier.

Hold the left hand cone still while you loosen off the thin locknut.

Lift off the thin anti-turn washer. Note the shape of the hole.

Use a Sturmey Archer cone spanner (if you have one) to take off the cone.

Put the left hand side of the axle in the vice, axle vertical and gripping the flats.

Ping off the circlip that holds the sprocket, dust guard ring and spacers.

Top spacer and sprocket. Note which sides of the sprocket you take the spacers from.

Second spacer under the sprocket. This gives the chain plates some room to clear the dust guard ring.

Remove the dust guard.

Mark the ball ring and the shell as the thread is twin start.

Knock the incut with a hammer and an old screwdriver and unscrew the ball ring.

Withdraw the gear mechanism.

This mechanism is dry in parts and coated with a tarry sludge in other places, which is unusual and bizarre.

There is no evidence of oil in the shell, just the black tar. Highly neglected hub gear.

It looks like wet grease but trust me, it's more like varnish.

View inside the shell. Lots more sludge to clean out here.

Put left side of axle back in the vice. Unscrew the right hand cone locknut.

Take off the tab locking washer that locates on the cone.

Unscrew the cone with cone spanner, then by hand.

The cone is actually in tip top condition and will run smoothly.

Note carefully the location of the collar on the outward end of the clutch spring. Remove the collar.

Pull out the clutch spring.

Pull off the 4 pronged driver. This carries the right wheelbearing.

Lift off the ball ring. This contains the driver ball bearing and the high side pawl incuts.

Lift off the annulus (ring gear) to reveal the three compound planets...

...and the four pronged clutch. Note that the clutch is pushed upwards by a spring inside the axle.

Remove the thin washer. This prevents wear on the clutch spring. Occasionally it can be missing.

Lift off the axle key collar.

Note the small incuts for the key.

Withdraw the axle key sideways by pushing out with a spoke or small screwdriver.

Pull off the 4 pronged clutch. There is no wear or damage at all.

Remove the clutch collar, shaped like a top hat.

Take the internal spring out of the axle. This can be pushed out with a pin through the slots in the axle.

Note carefully that the spring has a collar which goes into the axle first.

Hold the axle and spin the planet cage to allow the planet pins to drop out.

When they fall out of the planet cage the planets will also drop out. Then remove the axle from the planet cage.

Here are the compound planets. There is some wear on the small cogs but still plenty of life left in them.

The axle has two suns. The hub trigger control locks one or the other to the axle.

View of the inside of the planet cage. Lubrication should really be light machine oil, not tar.

The sun gear with ramped dogs gives first gear, and if the dogs were square it would be capable of producing a fifth gear.

There is no appreciable wear to the mechanism. These machines were built to last.

Here are all the parts laid out on the bench. There is still some further dismantling necessary.

Put the axle into the vice as shown and tap the locking washer flat...

Start bending the sides of the washer with a knife.

This locking nut has a curved face on the top side. Make a mental note of this.

Unscrew the locknut.

Pull off the thin washer below and note that it has an internal tab that fits into a groove onto the axle.

The small sun locking cup can be pulled off by gripping in the vice. My vice jaws are worn quite flat and did not damage it.

Axle off. Note that the small sun does not come off until the collar inside has been removed.

Here is a close up of the small sun locking cup. The teeth are undamaged so plenty more years left.

Put the axle back in the vice and pull both suns down to expose the small axle key.

Push the axle key out with a spoke or small screwdriver.

Here is the key. It has curved ends to match the collar profile.

Take off the sun collar...

...followed by the little sun...

...followed by the big sun...

...followed by the sun spring. This is the extra force you have to pull against going from 2nd gear to 1st.

Here is the axle wiped clean. the dogs are in top notch condition.

All of the axle components laid out on the bench. It's definitely worth dismantling the axle sub assembly.

I have put a sprocket back on the driver to help with taking off the wheel bearing retaining ring.

Ease the ring out with a strong screwdriver. It serves as a dust trap when there is grease in the U shaped channel.

The driver bearing surface is in very good condition and will run smoothly. These often get worn out.

Inside the driver, the wheel bearing track is also in excellent order which is very good news.

Here are the high gear pawls. The clutch arms press on the chamfered ends to disengage high gear.

Use a small screwdriver to ease out the high gear pawls. Watch out for the springs.

The annulus ring gear is in good condition which is usually the case. No chips or wear to the pawls and the springs are fine.

Ease up the driver ball retaining ring with a screwdriver. Work your way around with several small leverages.

Ring off. The balls look lubricated and shiny which is a good sign. They can suffer in some hubs.

Note that the ball track on the large ring should have one ball missing. This is correct in this hub.

Hub Gears

Sturmey-Archer FW 4 Speed Stripdown