Chris King BMX Disc

Informacje o towarze

Poziom trudności: Średni/Trudny
Czas potrzebny do wykonania: 120-180min (zależnie od dysponowanych narzędzi)

After publishing pictures of my bike I have had several people ask me about how it is possible for me to be running a Chris King disc hub on a mod.


This isn't as simple as: get a frame with a disc mount, buy a disc brake, and buy a king hub.


I am going to refer to the Monty Pr/Ti frame, which is probably the most popular mod frame with a disc mount.
What one has to do:
-Get the right brake and right rotor diameter
-Order a BMX hub with a ISO Disc shell
-Buy a 3mm thick sheet of steel (size 8x6cm will be good enough)

The brake:
If you want to set the brake up easily it's worth getting a post mount brake (i.e Avid or Hayes). This will save you a lot of trouble due to the additional adjustability of the caliper. If you've decided to buy a IS 51mm brake (ie. Hope Trials) there'll be more fitting work to do.
When ordering the brake, one must buy a 20mm larger rotor than the brake will take. For instance a Hope Trials rear with a 180mm rotor. Don't buy a +20mm adaptor with the larger rotor.

The Hub:
Go to this page: www.aspirevelotech.com
Write them an e-mail asking for a rear BMX hub with an ISO Disc shell. You should receive a reply straight away with all the extra costs (my guess is about 20-40 dollars extra). Wait 3-4 days for the hub once it has been dispatched by EMS.

The adaptor:
Now this is the tricky part. You will be needing a thick sheet of steel. Don't be put off by the mass (the sheet pictured below weighs over 5kgs). The adaptor once finished with will weigh no more than 50g.

What makes this difficult:
-Inappropriate tools - you will be working on a very hard piece of metal, and will need this done as accurately as possible
-Rounded off disc mount on the frame which is the greatest problem of them all.
-Precision work, yet with a bit of luck you will make an ideal adaptor.

Step 1
Screw the disc onto the hub. Place a 2mm thick washer between the frame and the hub on the NDS (you'll need to bend the frame slightly for these additional 2mm to go in, but don't worry, nothing will happen to it).


Mount the chain and align the wheel so that the disc doesn't rub against the frame (the wheel will have to be at a slight angle) and so that the chain tension is to your liking. Screw down the wheel.

Here's how you do it:
Because the wheel is at an angle, it will move slightly when screwing down one bolt. Therefore:
-Firstly set the chain tensioners in the right place (check that the disc isn't rubbing against the frame)
-Place the bike on the front wheel and bars so it stands upwards
-Mark the position of the tensioners for future reference
-Press down the wheel (lean on it) and tighten one bolt, then mark it or remember which it was. Then tighten the second one. The CK axle has a very strong thread so don't be afraid to screw them down with all your might.
You will benefit from this in the future if you need to remove the wheel and put it back in. Thanks to this you won't have to align the caliper again.

Mount the brake on your bike, lever on your bars etc. Place the caliper on the disc and then tie some rubber bands around the bar and lever so that the caliper is locked on the disc.


Now align the caliper so that the pads are ideally on the disc race and so that the disc doesn't rub against the body of the caliper. Look into it from the top to see wether the pads are well aligned on the rotor.


Hang some heavy objects on the spokes to keep the wheel down.


Now you've got the natural position of the caliper in relation to the frame. This is the position which the adaptor will keep the caliper in. Get a piece of cardboard and cut it out so that it fits the frame and draw the position of the holes on it (you might want to use a pen to punch through the cardboard and into the holes of the frame/caliper to align them correctly). Depending on the size of holes you are going to drill, this needs to be accurate or can have a tolerance of 1mm.



Take the metal sheet and using a sharp object (ie. a screwdriver) draw the outline of the cardboard adaptor.




Step 2.
Cutting it out ;)
You will want to work on a small piece of metal not a huge sheet, so cut out a simple shape and then grind it down to the exact shape you drew with the screwdriver.

This will take a long time and you will need a bucket of cold water to cool the adaptor down whilst working on it.



Step 3.
Placing the holes
This is the trickiest and most important part, so don't f**k it up or you'll have to start from scratch. Draw exactly where the holes are to be made (preferably using a thin pen, not as pictured below). Don't use a large drill straight away, first make a small hole, then a larger one. Depending on the grade of steel, you might have to use several drills before making the final hole. I used a 6.5mm drill for making the final holes.
Note that you can't make too big holes because they are too close to each other. However making a larger hole than the screw, will allow you to move the caliper arround once mounted.
Now, a short guide to making a good hole.

Mark it:


Puncture it:
Use either a small drill or a hammer and sharp tool to make a little puncture in the metal. This will stop the drill moving arround when you start making the hole.


Drill it:
Place the adaptor in a vice (the piece of metal on the picture is purely as an example) and screw it down properly. Lube the puncture with oil and start drilling having placed the drill in the small hole (this will stop it moving around). Remember that each metal and drill has its own cutting speed so don't rev the drill. Press it down fairly hard and keep it at a low speed. Lube it when it gets dry.




Step 4.
Getting it to work.
This step might be frustrating due to human beings being equipped with two hands only.
I presume that by now you will have an exact copy of the cardboard adaptor. Lets mount it on the frame.
We will need two screws and two nuts, plus some washers. M5 screws are ok for this purpose.



Screw->washer->adaptor->frame->nut (w/o washer!)
Make sure that the screws don't stick out far enough to scratch the disc. If so, use some more washers.

Now we need to align the adaptor. As I wrote previously, the disc mount on the outside of the frame is rounded off. Get an adjustable spanner and waggling the adaptor get it as straight as you can (looking from the rear). Make sure that the adaptor is firmly screwed down before doing this.

A diagram explaining why this needs to be done:

Dark gray - frame
Brown - adaptor
This is a bit exagorated, the thick red line shows the angle of the adaptor, and by bending it you need to get it paralell to the blue and red lines.

Grab the adaptor like this and bend away




Step 5.
Mounting the brake
This will take quite a while. Get out as many washers of different thickness as you have. The standard Hope washer kit will be enough. Be careful when picking up the extra thin ones, i got one jammed in between my finger and nail.

This is an example of washers I am using and which align the caliper correctly.


Screw it down.


Tips on aligning the caliper:
-Firstly check looking from the back of the bike, if the caliper is exactly parallel to the disc. If it isn't remove the caliper and go back to step 4.
-When you think you have aligned the caliper correctly (no drag) press the brake lever and look closely at the disc. If the disc moves to the side when pressing the lever, you will need to rearrange the spacing of the washers.

Step 6.
Make sure everything is screwed down properly and that no screws are rubbing against the disc (some poke out).

Well done!

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