Sunday, October 22, 2017

Brompton M6R: How to Remove and Install Rear Wheel

Undoubtedly, one of the problems that Brompton riders fear most is a rear wheel puncture. In order to remove the rear wheel to change the inner tube, many parts such as the chain tensioner and the gear shifting mechanism need to be disassembled. After that, they have to be assembled properly to ensure correct operation.

This can be a daunting task, and I did not have a good idea how to do it. Luckily, there are some instructional videos on Youtube that are helpful for guiding the novice through the steps. I shall attempt to summarize all the steps into easy-to-understand instructions.

As with all bicycle repairs, it is important to try them out at home, so that you can feel for yourself how everything works. If you only know in theory, and have not tried it out hands-on, you are unlikely to make a successful repair by the roadside.

Now, let's say you have a rear wheel puncture, first stop safely by the roadside, and see if you have these items with you.
1) Hand pump or CO2 cartridge
2) Inner tube or patch kit
3) Tire levers
4) Size 15 wrench

If you have all of these items, congratulations! You can now attempt to change the inner tube. If any of these 4 items are missing, then your only choice is to call for a cab or a friend to rescue you.

Next, put your Brompton into the "working position". If you have a mudguard or rear rack on the Brompton, you can put the bike into the position as shown below, resting on the back of the saddle. If you have a saddle bag or rear light mounted behind the saddle, you might need to remove it.

Working position for the Brompton with rear rack, so that the rear wheel can be removed easily. Ensure that the bike is stable as handlebar movement may cause the bike to tip over.

In this position, you are free to spin the rear wheel or remove it.

Next, spin the cranks and set the shifters to release all cable tension. This means that on the right side 3 speed shifter, set to gear 3, while on the left side 2 speed shifter, set to +. In other words, both shifter levers should be moved all the way inwards.

After that is done, it is time to disassemble the Indicator Chain and the chain tensioner.

To remove the Indicator Chain, first loosen the locknut and then unscrew the barrel so that it is disconnected from the inner cable.

Next, spin the Indicator chain anti-clockwise to unscrew it from the push rod inside the internal hub.

If done correctly, the Indicator Chain can be removed from the hub. Put it to one side and do not lose it!

At this point, remove the chain from the tension pulley of the chain tensioner. To do so, move the tensioner arm so that there is slack on the chain, then slide it sideways off the pulley. After that, you can remove the chain tensioner unit from the frame.

Take the size 15 wrench and loosen the outer axle nut.

Remove the outer axle nut and washer completely from the axle, and this is what you will see.

With the chain tensioner unit removed, this is what you see. There is one more inner axle nut on the drive side that clamps the rear wheel within the dropouts.

Remove the inner axle nut and the non-turn washer from the drive side of the rear wheel. Here are all the parts (chain tensioner not shown) from the drive side of the bike.

Also remove the axle nut and non-turn washer from the non-drive side of the rear wheel.

If you are removing all these small parts out on the road, it is easy for you to lose them in the grass, or have them roll off into the drain. Keep them properly in your pockets or a bag, or have a friend hold them for you.

With the axle nuts on both sides of the rear wheel removed, it is now possible to remove the rear wheel.

If your rear wheel has been punctured, the tire will already be deflated, and you can slide the rear wheel out between the brake pads easily. However, if you are like me, just practicing at home, then you will need to deflate the rear tire.

Some guides will instruct you to undo the cable fixing bolt on the rear caliper brake (using size 10 wrench), in order to open up the brake pads for the rear wheel to come out. However, I found that with the stock Brompton tires which are rather wide, undoing this cable fixing bolt does not open the brake pads far enough to clear the tire. This might work for slim tires, but in the end I had to deflate the tire to remove the rear wheel.

Size 10 wrench needed to loosen this cable fixing bolt on the rear caliper brake.

Should you undo this cable fixing bolt? My recommendation is not to loosen it, as it is hard to clamp the brake inner cable properly afterwards.

My recommendation is not to loosen the cable fixing bolt on the rear caliper brake. Instead, deflate the tire to remove the rear wheel. It will save you time and trouble as you will not need to reassemble the rear brake cable after that.

As said earlier, loosening the rear brake cable fixing bolt does not open the brake pads wide enough to clear the inflated tires, so don't bother.

With that, the rear wheel can be removed! After that, it is just the standard way of changing the inner tube. Although the whole process can seem tedious, it is actually quite easy once you are familiar with the steps.

Other than learning how to remove and install the Brompton rear wheel, my other objective is to change the inner tube and rim tape for the Brompton. The stock Brompton tubes use Schrader valves, and I want to change them to Presta valves to be common with all my other bikes. This makes it easier to pump all the inner tubes without having to switch between Schrader and Presta pump heads.

Stock rim tape on the Brompton wheel. They are actually using rim tape for 18" wheels, with a ETRTO size of 355.

As some of you may already know, the 16" on the Brompton is actually closer to 18". 16" wheels come mainly in two sizes, ETRTO 305 and 349. These numbers refer to the external diameter of the rims.

Dahon Curve D3 uses 16" wheels with rim diameter of 305mm, while Brompton uses 16" wheels with rim diameter of 349mm. Yes this is confusing, but what is means is that Brompton wheels are actually almost 18" in size. Comparing 16" 349 and 18" 355, these two sizes are almost the same, which means that rim tape and inner tubes can be used interchangeably without issues. However, tires are not interchangeable as the diameter difference of 6mm is too big for the tires to seat properly on the rim, if the wrong size is used.

Stock plastic rim tape removed. Double walled rim, with a deep center channel. This makes installing or removing tires easier.

Replacement Schwalbe No.4 inner tubes with Presta valves, and Velox cloth rim tape to withstand high pressure.

16mm wide rim tape is OK as it can cover the rim holes. Wider rim tape will also fit but it will make installing the tires more difficult.

With the inner tube and rim tape changed, and the tire reinstalled, the next step is to put the rear wheel back into the frame. At this stage, do not inflate the tire fully yet! Remember, we need to fit the deflated tire back through the brake pads first.

Once the rear wheel is back in the frame, you can reinstall the non-turn washers and the axle nuts on both sides. Note that the non-turn washer has a long leg and a short leg. The long leg goes into the hole on the frame, while the short leg will rest on the axle inside the dropout slot. Install it wrongly and you will deform the washer or the frame when you tighten the axle nuts. From what I see, the non-turn washers and inner axle nuts are the same for the left and right sides.

Ensure that the non-turn washers are installed in the correct orientation

Now comes the tricky part, putting back the chain tensioner. I was not following any guide at this point, as I was confident of putting everything back together properly.

What I did was to put the chain over the idler pulley of the chain tensioner...

...then put the chain onto the tension pulley! As you can see, the chain path is totally wrong as it did not run along the idler pulley at all. Negative demonstration.

The correct way is to first place the chain in between the idler pulley (shown here) and the sprocket, during fitting of the chain tensioner unit.

If done correctly, the chain tensioner unit will sit flush against the frame, with almost no gap between the sprocket and the chain tensioner. Reinstall the outer axle nut to fix the chain tensioner to the frame.

Next, loop the chain around the other pulley by moving the tensioner arm. For the correct layout, refer to the second picture above.

Next, take the Indicator Chain and insert it through the hole as shown here.

This is another tricky part as I had to take a flexible chain, and try to rotate it so that the threads will engage the push rod inside the hub. For a good 10 minutes, I was trying to rotate the Indicator Chain so that it will thread into the push rod inside, but it just could not engage. Suddenly I realised that I was rotating it the wrong way, no wonder the threads could not engage. The correct way is to rotate the Indicator Chain in the clockwise direction, to that the threads at the end of the Indicator Chain can thread into the push rod at the inside of the hub.

Thread it fully into the push rod. After that, connect the barrel located at the other end of the Indicator Chain to the inner cable. How much to screw in the barrel will be determined by the position of the Indicator Chain rod in the next step.

Shift the right side shifter (3 speed) to the second gear, as this is where the internal hub will be adjusted. When in gear 2, the shoulder of the rod should protrude out from the end of the axle by around 1mm as shown. This can be seen when looking through the side holes of the outer axle nut.

Shoulder of the rod is protruding from the end of the axle by about 1mm, which is the ideal setting.

Depending on whether the rod is protruding too much or too little, adjust the barrel on the Indicator Chain to move it. Remember, your right side shifter must be in gear 2 when making this adjustment.

Take a bit of time to get this adjustment correct, in order to ensure proper shifting performance and avoid gear skipping issues. Once satisfied, turn the locknut on the Indicator Chain to lock the setting.

With that, the rear wheel has been installed and the gear adjustment done! For the first timer, this is not easy as there are many intricate steps involved. I strongly suggest practicing at home at your own time, as what I have done, as hands on practice is always much better than just knowing the theory. The final step is to inflate the rear tire, and you are ready to go! All these should take around 15 mins with practice.

After trying it for myself, I find that this is actually not too difficult. The challenging part is to make sure not to lose all the small parts that you will need to remove, but the actual steps are quite easy to follow. Hopefully this can give you the confidence and knowledge to practice on your own, and not be afraid of a rear wheel puncture on the Brompton!

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