I have now seen 5 bikes with aftermarket sprocket set ups experience this issue since it happened to me so I thought i would post some pics how to ensure this doesn't happen to you. I posted on different mfg compatibility issues with respect to the flange and carrier that you choose. Here are the steps to ensure your setup works well for many miles and what happens when you get the set up wrong. It happened to me because I assumed that the measurement specs would be universal across mfg. Not so. In my case the back of the flange when assembled with the cush drive and carrier was not flush with the back of the sprocket/sprocket carrier. This caused the wheel spacer to cut a groove in the sprocket until it was flush resulting in a loose assemble. I caught it in time and fixed it. The nature of the cush drive dictates that the sprocket carrier will always be in a state of minute clockwise and counterclockwise movement as the drive flexes. The means that if the back of the flange and the back of the carrier are not flush on the spacer your going to have a loose sprocket (flange longer than carrier) or one that is bound to rotation (carrier sticks out past flange) You want a nice tight fit that when assembled and torqued to spec has a snug rotational movement. To assist in this I also smooth and polish the spacer surface and use a high pressure synthetic grease. So far 4500 miles on this and it looks new when I inspected it. Remember that the coice of cush drive components will of course affect this set up which throws another potential mfg wrench in the mix.
Pic 1 Flange and carrier with a flush fit
Pic 2 spacer on flange and carrier
pic 3 stock vs polished spacer
pic 4 wrecked $150.00 Sitta because the flange and sprocket were not flush and the spacer ate the aluminum
Notes
The Sitta sprocket is not compatible with the CNC flange. I had to make a 1.65mm spacer to sit on the flange to make this work. It is compatable if you use stock cus drive components. AEM Ti cush drive, no. You need the spacer
The CNC flange is even worse with the AEM carrier. I have this set up but im not using it. I would have to make a 2.5mm spacer
The AEM flange, AEM carrier and AEM Ti drive pins work. I did not go with this as I dont like the AEM flange
The CNC flange, CNC carrier work with the stock cush pins. Sketchy with the AEM Ti pins in fact not all the AEM Ti Pins went into the CNC flange holes (WTF?) I did not go with a whole CNC set up as I could not find a 520 41T sprocket in CNC.
How was that for simple?
Pic 1 Flange and carrier with a flush fit
Pic 2 spacer on flange and carrier
pic 3 stock vs polished spacer
pic 4 wrecked $150.00 Sitta because the flange and sprocket were not flush and the spacer ate the aluminum
Notes
The Sitta sprocket is not compatible with the CNC flange. I had to make a 1.65mm spacer to sit on the flange to make this work. It is compatable if you use stock cus drive components. AEM Ti cush drive, no. You need the spacer
The CNC flange is even worse with the AEM carrier. I have this set up but im not using it. I would have to make a 2.5mm spacer
The AEM flange, AEM carrier and AEM Ti drive pins work. I did not go with this as I dont like the AEM flange
The CNC flange, CNC carrier work with the stock cush pins. Sketchy with the AEM Ti pins in fact not all the AEM Ti Pins went into the CNC flange holes (WTF?) I did not go with a whole CNC set up as I could not find a 520 41T sprocket in CNC.
How was that for simple?
