Introduction: Build Yourself a Low Cost Alignment Tool for Carbon Gates Belt Drive
My Idworx tracking bike is equipped with a Rohloff 500/14 Speedhub and a Gates Carbon belt drive. The details can be found at https://en.wikipedia.org/wiki/Rohloff_Speedhub and https://en.wikipedia.org/wiki/Belt-driven_bicycle .
Belt and Sprocket replacement
Originally on the Rohloff hub a “screw on” sprocket was mounted. Gates switched to splined sprockets. You can convert the Rohloff hub to splined sprockets using an adapter. After I replaced my sprockets and the belt, the CDX belt produced a cracking sound. Especially when rolling backwards in the garage. I had carefully set the belt to the correct tension. The belt and gears were clean and undamaged. So there had to be another cause for the cracking. The “Gates Carbon Drive Technical Manual” explains the importance of accurate alignment. However, it is not explained with which tools you must perform the alignment. On a cycling fair I met a guy from the Rohloff agency in my country. The friendly technician explained to me that the alignment could indeed be the cause of the cracking. He also said that you can check the belt for correct alignment with a special laser tool.
What do you need for the home-made tool for checking the alignment?
1. A Laser Pointer. I used a “Brennenstuhl ECO LED Laser Light”. I bought it for € 7.50 at a local hardware store.
2. A piece of U-profile with an internal width of 12 mm. In my waste bin I found a piece of usable aluminum profile.
3. Steel box or U-profile for mounting the Laser Pointer. I used a piece of square steel tube profile of 30 mm x 30 mm.
Step 1: Intro
In my tracking bike the rear wheel is mounted in such a way that it is always fixed in the straight-ahead position. You cannot put the rear wheel in line with the front wheel like in an old-fashioned shopping bike with chain tensioners. My bottom bracket is eccentrically mounted in a sleeve that can be rotated in the frame. The belt is tensioned by turning this sleeve. By turning you change the distance between the axle of the rear wheel and the bottom bracket, and the tension of the belt.
The alignment of the belt can only be done by moving the front sprocket to the left or to the right. The sprocket is mounted on the crank with so-called chain ring nuts. It may be that spacers have already been mounted between the crank and the front sprocket. Alignment is done by using thicker or thinner shim washers. You may need to use even longer chain ring bolts if you need thick mounting shims. Use the appropriate special tools to loosen and tighten the chain-ring nuts.
Step 2: Alignment Tool
In the steel box profile you file a U-shaped opening with a diameter of 26 mm, to create a “bed” for the cylinder of the Laser Pointer. You drill a 4 mm hole in the aluminum U-profile. With a sovereign you chamfer the hole for a countersunk flat head bolt in the inside of the alu profile. With only one MAG spot weld you fix the 4 mm nut in the inside of the box profile. In case of thicker material you can also cut 4 mm thread into it.
Do not tighten the 4 mm bolt at this moment. It should still be possible to rotate the Laser Pointer on the aluminum profile for the calibration of the pointer. With mounting kit you fix the Laser Pointer in the U formed opening. Let the mounting kit harden well. After hardening, the alignment of our tool must be calibrated.
Step 3: Calibration
In the vise you clamp a piece of 60 cm (pure straight) square bar. You calibrate the laser beam by clamping the aluminum U-profile (without any play) over the bar. Then you align the laser beam, so that it always points over the center of the rod. Now tighten the bolt and check the calibration again.
Now the self-made tool is ready for use.
Step 4: Using the Tool
Place the U-profile over the drive belt in the middle of the bracket, with the pointer facing the rear axle.
The laser pointer should point exactly over the middle of the belt, at the place of the rear axle. In case of a deviation from the center, spacing rings must be added or removed between the front chain ring and the crankset.
Lots of fun with building the tool and with cycling!