Let's get right to the crux of it by saying, this conversion isn't for the faint of heart. Then again, if you mess up, good rear wheels are going for dirt on eBay, so take a breath, collect yourself, and let's dig right in!
Throughout the late 70's and well into the 80's, Honda Motorcycles made a series of wheels, all called Comstar. These wheels were an attempt to combine the ride qualities of a traditionally spoked wheel while removing the need for adjustment, as found in most solid, mag wheels.
Now, why does this matter? Mainly, if you own a mid-80's Honda motorcycle, you not only most certainly have one of these wheels, but you're probably rocking shaft drive too! Needless to say, the aftermarket isn't exactly filled with tons of alternative wheel options for mid-80's shaft-drive Honda motorcycles....aaaaah, now it becomes clear!
This Instructable is a way to show that while you can't always replace your wheel, you can modify it to match your needs. In my case, I wanted to convert it from a drum brake to a disc for my ongoing dual-sport conversion. Let me know in the comments if you get stuck....and on to the show!!!
Step 1: Prep Your Wheel
This part is fairly easy.
First, disassemble the entire wheel. Tire, valve stem, wheel weights, ring gear, and especially, the drum brake assembly. It's all gotta come off!
Second, chuck the wheel onto a mill or lathe and machine down the old drum brake. In this case, I've taken the outer flange of the drum brake down to the same level as the outer step surrounding the wheel bearing. In the pictures you'll see the progression down to the final height.
Step 2: Turn Your Adapter
For this part, you can use either a round extrusion or flat plate of aluminum or steel. Since the one I was using was a good-golly thick chunk without too much machining in it, I went with aluminum to save weight. Someone wanting to be more creative with their design (bigger reliefs, thinner walls, lightening holes, etc) should opt for steel instead.
First, round off the blank to the desired diameter. I went for just inside the webbing of the old cooling fins.
Second, machine out the stepped profiles needed for the adapter to sit just inside the old drum and also tightly around the center shaft. The goal it to get it to fit tightly in place without any bolts holding it. They come later!
Third, create your profile! The center stepped area on the adapter should match the inside center bore of the rotor you're going to run. I also marked (with a thin groove) the diameter of the disc's mounting studs and I tapered the outer edge to prevent the rotor from vibrating against it and causing high-pitched squealing. The knurling is just for fun and the overall thickness is up to you! Mine's 14mm :)
Step 3: Drill Your Mounting Holes
This one's really easy and quite quick.
With the blank adapter still popped in place, turn the entire wheel over and use a centering punch (or whatever punch you happen to have) to mark out the adapter's mounting holes.
Take it off the wheel and drill out the mounting holes, and while you have it on the drill press or mill, drill out the disc's mounting studs. Remember, these holes will be threaded, so be sure to drill them out to the correct sizes for your taps! The studs should match the rotor you're using and the adapter mounts should be M10 1.25mm pitch to match the original Honda specification.
Step 4: Mount Your Studs
I'm using M8-1.25 x 50mm studs for my rotors. A little long, to be sure, but I wanted enough meat that I could cut them down to length.
Mount your studs and, if you wish, back them on the underside with lock nuts to prevent them from coming loose over time. Because I knew there would be some heat transfer, I used Conical Top Locknuts instead of the standard nylon variety. I certainly don't want to have to worry about the nylon ones melting!
Step 5: Refinish?
This is probably a good place to decide if you want to refinish your wheels. I opted to go with a nice satin powdercoat for the entire thing which gives it a period 80's look without all the two-tone nonsense :)
NOTE: Paint adds thickness!!! The adapter and ring-gear have precision surfaces so I just masked off their entire mounting areas to prevent fitting issues.
Step 6: Final Assembly! Yay!!!
Use 5 M10-1.25 x 70mm long bolts to go straight through the ring-gear into the adapter plate. That's it!!
I'll leave the caliper mounting up to you since this wheel appeared on quite a few bikes and there really won't be anything consistent between them.
Enjoy your new found braking POWER!!!!!
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