Step 1: Parts & Supplies!!
•40, 41, or 50 SAE chain size
• Bike (preferably with sliding dropouts)
•PBI Aluminum sprocket
•3.5" 6061 solid aluminum or
•Hob sprocket cutter
•20 T rear steel sprocket as a pattern
•General shop tools and knowhow
Tree Fort Bikes has a rear steel sprocket
♦You will need a large front sprocket and a small rear sprocket for this conversion. Ideally you want aluminum because it is stronger per weight than steel which means that is is light!! PBI sprockets has blank aluminum motorcycle sprockets that we can use for this project. I suggest using a 32 T front and a 20 T rear; this gives a 1:1.6 gear ratio which is perfect for mountain biking.
♦Since PBI doesn't carry 20 T sprockets and we especially need one that is internally-splined, we must machine our own.
Step 2: Machining the Sprocket!
Lets get started!!
•You will need to cut a "disk" form the aluminum solid stock. (metal band saw - horizontal) This will be your aluminum blank.
1. •Next, using marking fluid or a Sharpie to color the aluminum so that you can SCRIBE the outline of the steel sprocket onto the aluminum blank. (I use Marks a Lot)
2. •After you have your scribed aluminum disk mount it in the chuck with outside jaws.
3. - Drill and Bore the inside of the sprocket to the minor diamiter of the free wheel bike wheel.
***Use a Drill bit closest to the size of the roller to drill the valley of each tooth in order for the chain to move freely. ***
Step 3: Final Finishing!
•Also trace and file the splines on the inside bore of the sprocket.
•Run the chain over the sprocket every once and a while until the chain fits well.
***You will spend lots of time filing unless you can machine the teeth with a hob mill!***
Step 4: Installation!
• In fact I just use PVC as the spacers.
Step 5: Further Development!
Fe bikes has some good info on bike building and more MONSTER chain ideas.
Note: I got lucky with the chain tension with vertical dropouts!!**
P.S. Please Vote for - for the bike contest!! (if you are so incline!)