Wandering chain tension

[SoCal250]

To rule out manufacturing issues (defects) with the chain you can measure sections of 10-14 links with calipers in different spots around the chain. Compare the section where it's tight to where it is looser. If it's not the chain then you have radial runout on one (or both) of the sprockets.

[Vintagewannabe]

To rule out manufacturing issues (defects) with the chain you can measure sections of 10-14 links with calipers in different spots around the chain. Compare the section where it's tight to where it is looser. If it's not the chain then you have radial runout on one (or both) of the sprockets.

This is my plan for my next move, as well as putting the wheel on a truing stand and checking sprocket runout in all directions, and checking bearings.

[Vintagewannabe]

So I pulled the rear wheel, and checked the sprocket, and bearings. Wheel bearings were perfect, cush drive is still good, looks like my carrier bearing has a bit of play, like if you were to try and twist the carrier on the axle, same way you check wheel bearings on the bike.
So once I had the wheel on the truing stand, I checked the sprocket and it acted out of round. Sat the wheel on the ground, and realized that around the carrier, inside the center bore of the rear sprocket there was a large gap on one side and none on the other. The taller area fell between the two green dots I made, which falls in line with all the slack in the sprocket being on that side.
So I pulled the rear sprocket and the center bore of the sprocket was 1mm larger than the hub on the sprocket carrier. Any other sprocket I have fitted has been a tight fit, but this one is definitely not, but I did not think much of it at time of install.
I have it back together, and now there is a much smaller variation in chain tension. About 1/4 in or less, vs the 3/4 it was.
Has anyone else had a sprocket that loose on the hub? I'm thinking of just ordering a custom one from sprocket specialists.

[m in sc]

actually, no but that def explains it. you always want the sprocket to be hubcentric.  if that's from economy, reach out to John. also, look into rebel gears, they may have one as well

[JKV45]

So I pulled the rear wheel, and checked the sprocket, and bearings. Wheel bearings were perfect, cush drive is still good, looks like my carrier bearing has a bit of play, like if you were to try and twist the carrier on the axle, same way you check wheel bearings on the bike.
So once I had the wheel on the truing stand, I checked the sprocket and it acted out of round. Sat the wheel on the ground, and realized that around the carrier, inside the center bore of the rear sprocket there was a large gap on one side and none on the other. The taller area fell between the two green dots I made, which falls in line with all the slack in the sprocket being on that side.
So I pulled the rear sprocket and the center bore of the sprocket was 1mm larger than the hub on the sprocket carrier. Any other sprocket I have fitted has been a tight fit, but this one is definitely not, but I did not think much of it at time of install.
I have it back together, and now there is a much smaller variation in chain tension. About 1/4 in or less, vs the 3/4 it was.
Has anyone else had a sprocket that loose on the hub? I'm thinking of just ordering a custom one from sprocket specialists.

Based on what you have posted previously, it appears to me that the sprocket has been the issue.

Not sure if you turned it 180 degrees when you reinstalled it, but there's a chance that could improve the inconsistent tension.

It seems like that sprocket is out of spec in a few ways.

[Vintagewannabe]

I am pretty dead set that the sprocket is my problem.
I didn't spin the sprocket, I just centered that extra slop that it has. I am going to make some calls to see if the numbers I got line up with the specs that economy cycle has, and the manufacturer rebel gears.

[1976RD400C]

It certainly shouldn't have to rely on the bolts to center it, it needs the hub to fit, like rotors and wheels on a car.

[RDnuTZ]

automotive wheel lug nuts are tapered on 1 end which does help center the wheel 

[m in sc]

there used to be bolt centric wheels,, or were more common  vw vugs come to mind. but the taper nuts are there so the load is spread out better. and not against the threads.  also a tapered nut has less chance of backing off. hub centric, way better  0.02

[Simoniz]

Good to see you found the solution to the weirdness. It's unusual to see one like this that is too big in the center. At least sprockets are easy to replace.

[Vintagewannabe]

So I am finally getting back on this issue after life getting in the way. I reached out to economy cycle a few times and didn't really get anywhere.
Talked to rebel gears and they said my sprocket was to spec and they have never had this issue with the RD350 sprockets. Has anyone else had this? The bike came to me bone stock so I doubt whe wheel was swapped or machined but its not impossible.

[RDnuTZ]

do you have another sprocket laying around to swap on there for a sanity check?

[Vintagewannabe]

do you have another sprocket laying around to swap on there for a sanity check?

theres a small chance I still have the sprocket that was on it but I need to dig around. My engine needs a rebuild so I will at least pull the sprocket and re measure everything then.

[Vintagewannabe]

Dug out the old probably stock sprocket. Center bore measures exactly 74. Which is also what JT sprocket says on their site. I think I will call sprocket specialists in the morning and see what they have as spec.

[1976RD400C]

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.