Wandering chain tension

[Vintagewannabe]

Took a look at a sprocket I had. The hole in oem sprocket fits tightly over a machined hub on the sprocket carrier. It is exactly 74mm in diameter. That centers it. That hub is only 1/2 as thick/tall as the sprocket so it looks like a gap between the two until you take the sprocket off.

Mine was the same way.
I called sprocket specialists and their spec is 74.37mm.
I am going to pull my sprocket apart again and re-measure to see if I got something wrong.

[1976RD400C]

An oem sprocket hole is exactly 74mm

[Economy Cycle John]

I measured several here were all 74mm. No other reports of issues with that batch or any with this issue, so not sure what happened here. The one you have is 75mm?

[Vintagewannabe]

I pulled the wheel and measured everything. The hub the sprocket sits on measures from 73.05 to 73.18 depending on where you measure. The sprocket center bore measures 74.35.
I put the carrier on a truing stand and I am a bit worried the carrier is out if round. Thinking back when I first got the bike, the rear sprocket was loose one day. I will post a couple pictures but there is a lip on the carrier where the sprocket sits that makes me worried the sprocket was loose for a long time and hurt the carrier.
I talked to rebel gears again, and since they are only an hour from me, they said I could bring my sprockets and carrier and they would help me figure it out.

[Vintagewannabe]

https://youtube.com/shorts/tr7hSFRzvts?si=GzzMYRXzE8qEHzHs

So these show the lip on the carrier that looks like strange wear.
The vid is just to show how much play there it.
I rolled the dice on an ebay part so we'll see if it is different.

[1976RD400C]

The oem parts I have are a tight fit, in fact I couldn't pull the sprocket off by hand after removing the bolts. Had to tap it with a brass hammer to get it to pop off.

[RDnuTZ]

https://youtube.com/shorts/tr7hSFRzvts?si=GzzMYRXzE8qEHzHs

So these show the lip on the carrier that looks like strange wear.
The vid is just to show how much play there it.
I rolled the dice on an ebay part so we'll see if it is different.

I suspect the fleabay part will solve the discrepancy. A SWAG on what happened to current 1? A previous clueless owner probably ran the bike without the lock tabs and never bothered to check the nuts were secure on there leading to lots of back-and-forth movement of sprocket.